I’m being quoted £x,000 to replace this!

[belfry]

We live on a remote farm with our house and other buildings being heated by a 10year old biomass boiler system.

We’re being told that our control panel needs replacing and that it is no longer available as many of the components are now obsolete.

A whole new control panel is likely to cost several grand and there is no idea of how long delivery might be.

I live in East Anglia and wondered if there was anywhere trusted to take the motherboards that I have removed?

We have no heating and no hot water and my family is not very impressed. The heating engineers don’t seem to be able to think beyond replacing the whole control unit.

Any suggestions very, very welcome! I attach some photos to give you some idea of what we’re dealing with.

[belfry]

Photo

[belfry]

Relays

[DavidAlfa]

I know nothing about this board, but what's the fault? Nothing obviously wrong at first sight.
Any electronics guy should be able to make some basic checking, testing those relays, power regulators, replacing capacitors if required... Even you could do it yourself if you have some soldering skills.
As long as the eeprom/flash memory is OK, the rest should be replaceable!

[belfry]

Thank you for your reply.
The boiler system keeps stooping and displays “Motor fault heat exchanger”, but the motor has been tested and seems to be working fine. I’m worried that the engineers are just suggesting throwing money at the issue (my overdraft!). They are adamant that the manufacturers will only supply a whole new unit due to some parts not being available any more.
Any suggestions of where I can take it? I’m off the Cambridge on Monday and I guess that there are likely to be some people or firms they who might help.

[Terry Bites]

Does the motor actually start turning when the system demands it?
If not, it could be a motor drive or switching failure on main PCB- that could be as simple as a duff relay.
Try and trace that relay. Can you feel it (light touch) clicking in or out?
Unsolder it and test it. Relays are cheap and easy to source.
It could also be a proplem with valves failing to open, again check apropriate control relays.
Pressure switch?

If its not the motor it maybe a sensor attached to the motor that's faulty. Something in there checks its running. A flow sensor?
The sensor input circuit on the pcb may have problems.
google maps "electronic repairs near me".

[bookaboo]

The company I work for used to have a contract to service these types of PCB. There’s an inherent design flaw in the PCBs, the relays are under rated for the application…. Basic stuff but the designer got it wrong.

It will only be one or two of the relays giving trouble , a good technician will be able to tell you which of them isn’t working.

There may be some local electronics repair shop that can replace the relay(s) for you. If not search for Electrotech Solutions….. based in uk and do a decent job.  Just make sure to tell them it’s relays only.

Bad news is it will happen again in 18 month. We advised our customers to fit proper contactors on the functions that were burning out.

This design flaw is endemic in these systems, and the companies responsible are benefiting from their own errors.

[bookaboo]

The relays I refer to are the orange ones.

Also if you are really in a panic see if radwell or lektronix have a repair shop local to you.

[Ian.M]

No-one can fully diagnose the motherboard without a test jig that pretends to the motherboard to be the rest of the system, faking sensor inputs and showing the tech what outputs the board is activating.  However independent component level repair has been in a severe decline in the UK for several decades so the chances of anyone other than the manufacturer having such a test jig are minimal, and they've told you they no longer support it.  To some extent, the system is its own test jig, but that means you need a field service tech with component level repair experience, who (if you can even find one) will charge an eye-watering callout fee and hourly rate with no guarantee of success. 

As David and Terry have pointed out, even without a test jig, easy faults like a failed PSU or a burnt PCB mount relay can probably be found and fixed by a good independent repairer, *IF* you can give a good enough fault description, which needs to be specific to which outputs are bad, but few customers are capable of that, so most repairers will be very reluctant to accept such work on a board they aren't familiar with.  If you have *ALL* the system documentation and wiring diagrams with you, it *may* help overcome their reluctance.

[voltsandjolts]

The boiler system keeps stooping and displays “Motor fault heat exchanger”, but the motor has been tested and seems to be working fine.

The photos suggest this system is around 14 years old. Is the pump the same age? Are you really sure the pump is good? I mean, could it be that after some hours running the pump gets somewhat hotter and perhaps starts to seize, draw more current and trips out the system as you describe? If not too expensive, I'd replace the pump first, just to guarantee it's not the problem.

[jpanhalt]

There is a lot of paperwork along side it.  Does it give error codes to help localize the fault?

I have what we call a hydronic heating system.  It uses hot water to heat the house and the domestic hot water is produced by a heat exchanger with the heating water.  There's a boiler, 2 pumps, lots of water pipes.  I use propane for the power.  Originally there was both an indoor wood burner and outside wood burner that added 2 more pumps.  In other words, aside from my heat source, it might be similar to your system.

My control panel went bad about a week after I bought the place in 2010.  It was cycling on off and no heat.  Similarly, it was obsolete, but a new panel was only $200, it was freezing outside, so I got it.  Later, I took apart the old control panel  It was less complicated than yours (house was built in 1993, but similar.  The solid state stuff rarely fails.  The problem was the small "logic" relays -- about half the number of orange things on your board. 

Sorry for the long lead in to my suggestions:   
1) Those relays look like standard footprint control voltage level relays.  Identical brands may not be available, but there are inexpensive substitutes.
2) If you cannot localize the fault to a single circuit/couple of relays, buy a bunch.  Otherwise, buy what you need to replace them and replace suspect relays in that motor circuit.
3) The motor may be fine, but there is probably a boiler fan and other things that need servicing.  My boiler fan gets oiled once a year.  A replacement is about $100.
4) Check that the pumps are working.
5) My system had a bypass valve between boiler input and output.  Its purpose was to give a quick temperature rise in the boiler and reduce water condensation in the flue.  At 30 years, it stuck open.  I got rapid cycling, an overheat situation, and the house temperature rise was limited to only about 10° above outside ambient.  I removed the valve and added a drain to the flue.  It has a water trap to prevent gases from entering the house.

If your system is like my system, I would look at #5 first, then #1.  Solid state devices rarely fail.  Mechanical (e.g., blowers, relays, and valves) are the most likely failure points.

[mikeselectricstuff]

I'd agree that a relay contact, or possibly coil,  is a fairly likely cause.

I'd use a meter to trace the motor connection to find which relay it goes to. See if that relay clicks on when it should and check the voltage across the motor.

You may even find that tapping the relay when it's supposed to be on may show some life and/or some visible arcing inside the relay.


If it's not something you want to tackle yourself, the only thing I can think of is maybe talk to a small electronics assembly house - they will usually have at least one test engineer who could probably sort you out if asked nicely

e.g. https://protronics-uk.com/about-2/


 

[jonpaul]

Find a licensed electrician in your area familiar with industrial controls, contactors, 240/480VAC safety.

All the relays and contactors are STILL made and available.

Bon chance,

Jon

[mikeselectricstuff]

Find a licensed electrician in your area familiar with industrial controls, contactors, 240/480VAC safety.

All the relays and contactors are STILL made and available.

Bon chance,

Jon

The avarage uk electrician (we dont have licensing here) would not have a clue about this sort of stuff

[DavidAlfa]

If you have any small 5/12V wall adapter, a cheap soldering iron and a basic multimeter, you could do this yourself within an hour or so, it's very easy, any doubts will be quickly solved by forum users .

Meanwhile, post some high-detailed top/bottom pictures of the relay board!
Might sound dumb, but have you tested the fuses?

[belfry]

Here is a photo of the back of the board containing the relays. I have ordered 13 of the orange ones RT314024 and 6 of the black ones MP240D4. I am happy to replace all of these myself (although I will have to google how to remove a multi pin relay with just one soldering iron!).

[jpanhalt]

Those Crydom MP240D4 (black) relays are solid state relays.  I don't know what their failure rate is.  Mechanical relays have a high rate of failure.

[Twoflower]

There is a black solder joint (top middle of the underside picture). Can you check if the solder joint is OK? That doesn't look good.

If you're lucky that could be the reason for your problem.

And check the blue devices close to the SSRs on the right side, there seems some black snot there. Especially the upper one.

[DavidAlfa]

Soot will stick to high voltage traces, looking like this, though nothing being actually wrong.
If it was a hotspot it would look a lot worse!
To remove the relay, get a solder sucker, desoldering pump or whatever it's called:

[BillyO]

There is a black solder joint (top middle of the underside picture). Can you check if the solder joint is OK? That doesn't look good.

If you're lucky that could be the reason for your problem.

And check the blue devices close to the SSRs on the right side, there seems some black snot there. Especially the upper one.

Yup.  2nd pin of the X3 connector.

There also seems to be a bit of soot on the board.  What was under that board?

[belfry]

Here is a close up of that black pin on X3. Is there a simple way to test it for continuity? I have a couple of multi meters.

[belfry]

That joint was over this area. Bottom rhs.
This is getting exciting!

[DavidAlfa]

Can't see that last attachment? Getting 404 error.

[BeBuLamar]

Thank you for your reply.
The boiler system keeps stooping and displays “Motor fault heat exchanger”, but the motor has been tested and seems to be working fine. I’m worried that the engineers are just suggesting throwing money at the issue (my overdraft!). They are adamant that the manufacturers will only supply a whole new unit due to some parts not being available any more.
Any suggestions of where I can take it? I’m off the Cambridge on Monday and I guess that there are likely to be some people or firms they who might help.

I would try to find out how the board knows if the motor is faulted. If the motor is controlled by a single contactor then it's fairly easy to find out how the board determing if the motor is bad. We can go from there. if that is the case I am afraid the problem is still there after you replace the board.

[belfry]

Try this

[RayRay]

Here is a photo of the back of the board containing the relays. I have ordered 13 of the orange ones RT314024 and 6 of the black ones MP240D4. I am happy to replace all of these myself (although I will have to google how to remove a multi pin relay with just one soldering iron!).

Let me give you a quick tutorial, for starters, the tip you're gonna use with your soldering iron matters! A standard conical tip would be useless here. You'd wanna use a large tip for optimal heat transfer (such as BC3/BC4 bevel) but I'd have to know the model of your iron in order to provide a more specific recommendation. Apart from that, you'd wanna use a temperature of 360/370C, and add a bit of fresh solder to each pin before desoldering, as this would make the process easier, and you should preferably use leaded 63/37 or 60/40 solder for this purpose if you can obtain it in your country (as it's more desoldering friendly than the lead-free stuff) and also, I'd say 1.0MM diameter would be ideal here. For the desoldering process itself, you should use solder wick (desoldering braid), a desoldering pump, or both. Good luck.

[mikeselectricstuff]

Here is a photo of the back of the board containing the relays. I have ordered 13 of the orange ones RT314024 and 6 of the black ones MP240D4. I am happy to replace all of these myself (although I will have to google how to remove a multi pin relay with just one soldering iron!).

Let me give you a quick tutorial, for starters, the tip you're gonna use with your soldering iron matters! A standard conical tip would be useless here. You'd wanna use a large tip for optimal heat transfer (such as BC3/BC4 bevel) but I'd have to know the model of your iron in order to provide a more specific recommendation. Apart from that, you'd wanna use a temperature of 360/370C, and add a bit of fresh solder to each pin before desoldering, as this would make the process easier, and you should preferably use leaded 63/37 or 60/40 solder for this purpose if you can obtain it in your country (as it's more desoldering friendly than the lead-free stuff) and also, I'd say 1.0MM diameter would be ideal here. For the desoldering process itself, you should use solder wick (desoldering braid), a desoldering pump, or both. Good luck.

Wick doesn't usually work well on through-plated  holes like this, as it tends to only remove about half the solder nearest the iron, as the solder deeper in hasn't melted, and the top solder being removed by the wick stops the heat transfer to melt the deeper solder.

The trick with a sucker is to make sure the joint is heated long enough to melt all the  way through - adding a little extra solder can help - if the original is leadfree, adding some leaded can help as it flows better and reduces the melting point.
Once each pins are desoldered, wiggle it around to ensure it has fully desoldered all the way round, to avoid the risk of damaging the through-plating when you pull the component out. 

[xrunner]

Thank you for your reply.
The boiler system keeps stooping and displays “Motor fault heat exchanger”, but the motor has been tested and seems to be working fine. I’m worried that the engineers are just suggesting throwing money at the issue (my overdraft!). They are adamant that the manufacturers will only supply a whole new unit due to some parts not being available any more.
Any suggestions of where I can take it? I’m off the Cambridge on Monday and I guess that there are likely to be some people or firms they who might help.

At the risk of providing "too much help" ...

Does the motor drive a fan for the heat exchanger? If so does the motor run at all, and then stop running, or does it not run at all for any length of time? Are you standing by it to observe this?

Reason I ask is maybe they sense an overtemp via a sensor, and the designers decided the motor not running is the logical cause of an overtemp (since the fan would then not be blowing across the exchanger). Perhaps the sensor is the cause (it failed) but they give you a message that the motor is not running.

I recently had something along those lines happen to the windshield washer tank in my car. The error LED came on my dash, which indicates that the fluid is low. However the fluid was not low, it was full. The problem was the sensor in the tank had failed (the float inside had dissolved making the magnet fall down tripping the microswitch instead of floating up. So sometimes the designers assume the sensors are OK and if they fail, they simply tell you whatever it was sensing is the problem instead of the sensor being the problem.

[Gyro]

Given that the thing is 10-14 years old, it is probably worth going around and checking the tightness of all of the terminal screws (with proper attention to mains risk). I don't know if the controller is sited in an outbuilding but a loose terminal combined with a bit of oxidation could easily mess up a sensor signal.

[HackedFridgeMagnet]

The contacts on the relays are hard to check without live testing, which would be hard or unsafe.
Alternatively you could just bulk replace them all. 

"Mr solder fix it" can help you to get out those relays.

https://youtu.be/Vou2xlJkuoU

https://youtu.be/0b_AA7uj388

https://youtu.be/D-un9-ZsSQI

[Ian.M]

Its easy enough to test the mechanical relays on the relay board.  Look up their coil voltage in the datasheet.  Trace out the circuit for one channel.  Then all you need to do is put just the the relay board on your bench, power it  with the nom. coil voltage, preferably from a current limited bench supply, and apply a logic signal to the input pins on the header that normally connects to the control board one input at a time to activate the corresponding relay, which should click.  You can then measure the resistance of its N.O. contacts when closed, (and also measure its N.C. contacts when its not activated) and compare with a known good relay (e.g. one you bought) or the datasheet. 

A bad mechanical relay either wont click, or one or more contact resistance readings will be excessive, or vary erratically when you tap the board.

The Crydom solid state relays are harder to test as they wont give meaningful readings on an ohmmeter, because they need AC, min. 24V RMS on their 'contacts' to operate correctly.   You could set up a test jig with a 24V transformer, a 10W incandescent 24V truck bulb wired in series with its secondary, and two probes, connect them to the relay output (pins 1 and 2), then test by applying an input signal to the board at whatever pin you've traced to that relay.   

[sarahMCML]

Any idea what the battery shown in the top right corner is for? It may only be for timer backup, or it could be holding the contents of a calibration memory chip. Might be worth testing it, in situ if possible. It is around 15 years old after all!

[p.larner]

if it was mine i would be thinking of making a replacement pcb and fit  better relays and connect them using fly leads,

[mikeselectricstuff]

if it was mine i would be thinking of making a replacement pcb and fit  better relays and connect them using fly leads,

The original ones have lasted 10 years, seems overkille

[p.larner]

at least it would make it better to ork on if the relays were changed for socketed ones and the board mounted so its easy to get at with beefier relays.

[killingtime]

>>We’re being told that our control panel needs replacing and that it is no longer available as many of the components are now obsolete.

Contractors usually trot that line out when they don't know what's wrong, so they try and get you to replace the lot.

The issue could be anywhere in that box, from a relay contact to a loose cable or terminal screw or component on the PCB, so the fault needs diagnosing first. Only then will you know if the system is a write off. Could be a simple fix. I wouldn't try and diagnose it yourself as there is mains voltage involved. Your call.

I would go with the suggestion from jonpaul. Keep ringing heating technicians until you find someone that can diagnose the problem. Given the complexity of the system, I'd also try calling commercial heating engineers. Panels like that are normal for large buildings. It might take 4 or 5 different inspections before you find someone that knows what they're doing, so don't give up.

[Nusa]

if it was mine i would be thinking of making a replacement pcb and fit  better relays and connect them using fly leads,

Diagnosing and fixing the immediate problem comes first here. Fixing stuff that probably isn't broken is for later.

[u666sa]

heated by a 10year old biomass boiler system

 

What?

I mean, where I live we have natural gas, either through pipeline, or in large underground storage, or wood, or wood & coal combination, or electricity, or in my case in the city I'm paying $25 a month during winter for heating. You gave a mouthful of space age technology I have no clue about. What is a biosmass boiler? 

Anyway, your problem is similar to washing machine




What you mostly likely have is a bad solder join problem. Post good hi-res picture of the back side of the board above, with lots of light so we can see things clearly.

There are two approaches to fixing it.
A. Find out which relay is doing what, and touch up solder joins of relay that is responsible for doing thing that is broken.
B. Touch up all solder joins, especially those that look bad.

Plus you'd have to check those 3 fuses, and possibly check every relay. (but relays rarely go bad, so you can skip this step and focus on bad solder joins and fuses)

[chinoy]

There is this russian guy who runs a youtube channel. Where he repairs mostly phones and laptops. But he tries his hand at anything. He is based out of the UK and charges you by the hour.
I am fascinated by how he undertakes complex repairs with zero schematics just using common sense and logic.
id give him a shot. People mail him stuff to repair from all over the world.
If you cant find him let me know Ill try and dig up a link.

[BeBuLamar]

I don't trust anyone who claims to use common sense.

[chinoy]

Here is his web site address.
https://sorinelectronics.com/

Here is his youtube channel where I learned a lot over the years.
https://www.youtube.com/@10minlaptoprepairs/videos

Ps: I don't know the guy. Not involved in anyway with his business. Just watch his videos to learn.

[u666sa]

Wick doesn't usually work well on through-plated  holes like this, as it tends to only remove about half the solder nearest the iron

For this stuff desoldering gun is best, but a newbie or just DIY-er won't have it. The suction thingy is pretty bad, so I wouldn't spend my money on it. If desoldering is needed, I guess the relays, OP should buy low melt solder, rose's metal for example, and use it to take off the relay, and then solder wick to empty the holes.

But, I repeat.......

Chances that one of the relays is bad are low, they usually don't go bad.

Most likely cause is bad solder joint. Most likely on one of these relays. Most nearly all washing machines have similar problems, when they go bad and give you some errors it is usually bad solder joint on one of the relays. So a solid repair for this situation OP has with his skill level and tool set is to touch up on all of those relays using some solder and some flux, preferably gel wash free flux and 60/40 solder. Then wash using flux off and toothbrush.

[807]

The very first thing I would do, is to redo the joint on that relay. It doesn't look good at all.

If there are any other joints like that, then redo them as well.

[CJay]

I'm good with anyone learning to solder, repair stuff etc, especially when it's something relatively simple like a relay board

But, given the cost of replacing this and the controller board I think the very first thing I would do is find someone who can work on a double sided plated through hole circuit board rather than learning to solder on it.

There's potential to cause, at best, quite heavy financial costs not to mention the ire of your family if you make a complete balls of it and, if you do make a balls of it then bodge it up there's potential to cause injury and maybe even worse if you get it wrong and something doesn't switch off or on when it's supposed to.

I'd perhaps try contacting one of the companies who refurbish 'normal' boiler controls and ask them if they'd replace the relays for you, they should also have liability insurance which would help if things go bad.

[wasedadoc]

..but relays rarely go bad..

@u666sa

Have you read reply #6 ?

[mikerj]

I've repaired quite a few gas combi and oil burner control boards and by far the most common faults are bad solder joints (from thermal cycling) and bad relays.  Bad connectors (oxidised contacts) are also up there.

[EPAIII]

Yes, that joint does not look good. It should have the old solder removed, things cleaned with a small wire brush (2-3 mm size), and fresh solder applied - probably with some fresh flux as well. I would use a solder sucker to remove it.

If you don' t feel comfortable doing that, any computer repair shop should be able to do it. Or appliance repair if you have that.

The very first thing I would do, is to redo the joint on that relay. It doesn't look good at all.

If there are any other joints like that, then redo them as well.

[tooki]

Chances that one of the relays is bad are low, they usually don't go bad.

LOL what?!? Relays go bad all the time. They’re electromechanical devices, so they can physically wear out. Coils fail open. Contacts weld closed (especially if the wrong type of relay is used for the application.) There’s a reason relays are often socketed, and that solid-state relays have taken over in many applications.

[BeBuLamar]

I must agree! Although any component can go bad as well as bad solder joint but on a board like that the relays are the most likely components to fail in time.

[Infraviolet]

My suspicion is that unless you can get hold of schematics for that board, you'd actually have an easier time (easier, not easy) designing a board from scratch to interface with the same hardware this one controls, than you would trying to debug a fault in a device you haven't enough information about. Unless you could be sure the fault was in the right-hand "lower" board, there's not much you could debug without scehmatics. The left-hand "upper" L shaped board has lots of IC chips on it, many of which could be running software of various forms and communicating with one another. One of these could have failed, and even if you replaced the chip (and it was of a type still in production) you'd have no idea what code you'd have to have it running. The lower board though looks like a failure on it might be located with a lot of time, an ohm-meter, and using the somewhat repeating structure of it to look for situations where the conductivity measurements in one repeated section don't match the equivalent measurements done of another section of the same layout.


If you can't get schematics for the board but can get an explanation of what all the wires which connect in to it do, you could design a replacement board? If you can't get that explanation of the wires, though I suspect there's a good chance that atleast they would all be explained in detailed service manuals, the only hope would be to find a working one somewhere and use some sort of logic analyser to monitor what each of the wires does. This would be a lot of work, if you couldn't do it yourself then the time taken would mean hiring anyone would likely cost as much as the £x000 you're being quoted already.

[BeBuLamar]

The board reports "Moto fault heat exchanger". Ok the motor is good but how does the board knows if the motor is faulted? Most of the time it only check on contact some where. I would try to find this out.
Designing a board is OK but there is safety involved.

[LinuxHata]

So it is quite easy to check, and no need for complicated knowledge.

From my practical experience of debugging such systems, most likely faults were due to either current sensor, pressure sensor or relay failure.
 
First of all, how system knows that motor is OK? it either checks the current consumption of a motor, or there is a pressure sensor next to motor, so when motor is on, pressure change is detected. We need to rule out both situations.

We know the location of motor, right? So it should be possible to connect small incandescent light bulb to parallel to it. So after it is done, we should check the following, as power is applied to system and moment, where motor should start spinning.

Does lamp come on or not?
If it does, so should do the motor, let's check motor too. If motor is ok, proceed to the next next step.

If it does not, this means that there's a fault in a way of the power, we need to find it. To do this, disconnect the board from mains, disconnect the motor and apply small DC voltage, say 3 volts, from battery or whatever, to motor terminals. Using the multimeter, trace the voltage backwards, to see from where it comes. At certain point, you should "meet" the relay or other kind of switching device, past which your battery current won't go, since device is in offline stage. After you have identified that device, you need to check the voltage on it's contacts while system is operating (do this carefully!) Motor should be connected as usually it is. So when system is started and motor should be on, if there's a voltage (usually, full or almost full mains) on contacts of that switching device, it is not operating properly, since it should be in engaged state and show zero voltage drop on it. So the switching device needs to be replaced, but still, there are some chances that it simply does not receive the statement to execute. Similarly, if there's a half mains voltage or whatever on open contacts of a switching device, it still might be faulty and needs replacement.

But what if there's no voltage at switching device at all? Most likely, there's a blown fuse somewhere on the way of the power line, so you should again disconnect from the mains, and continue to trace the power delivery path, but this time, bypassing the switching device. Once you see the interruption on the power delivery, here you are, here's the faulty component which needs to be replaced.

Another issue is, when motor spins, but system believes it does not. This usually happens either to faulty pressure switch or current sensor. The pressure switch can be easily checked - usually it is next to the motor, in line with piping and has two contacts,  which usually make contact under the required pressure only. So just connect multimeter to these contacts (disconnecting the wires going to it),and check for continuity - it should change when motor starts. If not, pressure sensor is faulty.

There are other, obvious possible causes of the problem, like clogged piping, but I guess, these were already ruled out?

 

[mikeselectricstuff]

My suspicion is that unless you can get hold of schematics for that board, you'd actually have an easier time (easier, not easy) designing a board from scratch to interface with the same hardware this one controls, than you would trying to debug a fault in a device you haven't enough information about.

Utter nonsense.
The thing did work, therefore it is a failed part or component. There is no way that even replacing pretty much every part would be anything like as much work than designing & debugging a whole new board.
I've fixed dozens, if not hundreds of things with no service information. OK it takes longer as you need to work out how it's supposed to work before you can figure out why it doesn't, but on a device like this it really shouldn't be that hard.

[pickle9000]

Mike is right. Don't get fancy.

Try not to make the situation worse. Don't play with the ribbon cable they can be delicate with age. Get a practice circuit board
with some thru hole connectors and a soldering iron and practice a bit so you know what you are getting into.

[Bud]

The board reports "Moto fault heat exchanger". Ok the motor is good but how does the board knows if the motor is faulted? Most of the time it only check on contact some where. I would try to find this out.
Designing a board is OK but there is safety involved.

Is it a fan motor? It may have an air pressure sensor and the board may be checking the sensor.

[Gyro]

If there is a pressure or airflow sensor, it could be physically blocked or stuck. Worth checking, it's probably more likely than an electronics fault.

[jmelson]

I see a board full of relays.  These have markings on them.  We had an old washing machine with similar relays that had no surge suppoessors on the contacts and they burned up the contacts.  A good guess is that those relays may be bad.  You may be able to order replacements and solder them in.
If the whole controller has gone bad, then maybe you SHOULD replace it.
Jon

[pickle9000]

I see a board full of relays.  These have markings on them.  We had an old washing machine with similar relays that had no surge suppoessors on the contacts and they burned up the contacts.  A good guess is that those relays may be bad.  You may be able to order replacements and solder them in.
If the whole controller has gone bad, then maybe you SHOULD replace it.
Jon

The controller gave some error message so it's probably just fine. As for sensors often the designer
will do a timeout error. For example on a furnace controller there may be a few temp sensors but none
on the blower motor. If the temp rise does not follow whats expected then the controller may say
blower motor failure and shut down. In reality a faulty relay or whatever on the output can cause the
same issue. Relay's offer very good protection to a controller and that is why they are often used.

[ttx450]

I cant get over the complexity and amount of wire plug ins.. for aq boiler.  You must have many zones and other stuff.  Crazy board replacement price. It would be interesting to know/see how this is wired and all the zones and what ever else is hooked to it.  Good luck, winter is coming.. post progress. 

[Nusa]

He did say up front it was for a house and other buildings on a farm.