Author Topic: Electric shower, anything I can do?  (Read 12547 times)

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Offline paulcaTopic starter

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Electric shower, anything I can do?
« on: July 23, 2019, 06:55:35 pm »
So, new house, has electric shower.  Shower has three settings, cold, low, high.

On low, when I turn it up enough to get good temperature, I get sod all flow/pressure.

On high, I have to turn it down to minimum or I get scalded and even then it can overheat and cut out occasionally.

So I guess this is because my upstairs water pressure is absolutely rubbish.  On low it uses a smaller element and when I turn it up it reduces the flow to make it hotter.  However on high there isn't enough water pressure to supply the element with enough flow to keep the temp reasonable.

I assume there is nothing I can do with that, like adjust the flow restrictor or something?

I'm planning on upgrading the whole heating system to a pressurized setup, so this is a temporary problem, but an annoying one!
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Offline soldar

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Re: Electric shower, anything I can do?
« Reply #1 on: July 23, 2019, 07:47:30 pm »
I take it you are dealing with an "on demand" heater which heats the water as it goes by? In America they also call them "tankless".

I have a natural gas tankless heater and they are crap. You cannot enjoy a shower with stable temperature. And if your pressure and flow are not stable it makes the situation so much worse.

In my second home I have a big tank heater and it is much better. And you can even fit a thermostatic valve and temperature stability will be rock solid.

For a good shower you want a good tank of hot water. It does not need to be very hot, just 40 or 45ÂșC will do so you only need to mix very little cold water. Excessively hot water temperature is dangerous and should be avoided.
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Offline Nusa

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Re: Electric shower, anything I can do?
« Reply #2 on: July 23, 2019, 08:21:06 pm »
Dangers of talking to an international audience. Terminology isn't clear, since in America most people would ask "What's an electric shower?" In this case, I'm assuming a point-of-use on-demand water heater, either in arms length from the shower or actually in the shower head itself.

His other comments make me think he's on a gravity-fed system, using a cistern up in the attic space. Something else that's almost unheard of in American residences. Naturally pressure sucks if the vertical drop is small.

I also presume that new house means old house that is new to him. Or he would have a more modern setup to start with.
 

Offline ebastler

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Re: Electric shower, anything I can do?
« Reply #3 on: July 23, 2019, 08:36:12 pm »
So, new house, has electric shower.  Shower has three settings, cold, low, high.
On low, when I turn it up enough to get good temperature, I get sod all flow/pressure.

As others have pointed out, your terminology is not self-explanatory, especially to those in other countries. I take it that "low" and "high" are settings which affect the heating power? While, when you talk about "turn it up", you mean the flow rate - right?

Quote
On high, I have to turn it down to minimum or I get scalded and even then it can overheat and cut out occasionally.

Now you have really confused me. If you set the heating power to high, I could imagine a situation where you have to crank the flow up to maximum, because otherwise the water gets too hot. But you need to turn it (the flow?) down to minimum?! What's going on??
 

Offline themadhippy

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Re: Electric shower, anything I can do?
« Reply #4 on: July 23, 2019, 08:55:52 pm »
try reducing the flow out of the shower,not the flow into the shower ,a washer between the pipe and rubber washer in the shower hose  was the old skool way,or get an adjustable flow shower head
 

Offline Brutte

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Re: Electric shower, anything I can do?
« Reply #5 on: July 23, 2019, 09:07:26 pm »
I'm planning on upgrading the whole heating system to a pressurized setup, so this is a temporary problem, but an annoying one!

Before you rip apart whole plumbing, I'd suggest temporarily installing a manometer (just screw it to a tap) and doing some measurements. It might be that your heater is going to work just fine if you reduce the pressure on the input and stabilize it. Include winter temperatures in your calculations, leave some headroom.
 

Online nctnico

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Re: Electric shower, anything I can do?
« Reply #6 on: July 23, 2019, 09:12:45 pm »
A more simple solution is to add a regular thermostatic valve to the output of the electric water heater. That way it will keep the water output temperature constant. These are pretty cheap if you can do with a temporary crappy one.
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Offline soldar

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Re: Electric shower, anything I can do?
« Reply #7 on: July 23, 2019, 09:36:00 pm »
A more simple solution is to add a regular thermostatic valve to the output of the electric water heater. That way it will keep the water output temperature constant. These are pretty cheap if you can do with a temporary crappy one.
Will probably not work. I have some experience with these issues. A thermostatic valve will work when you have two streams at relatively constant pressure and temperature but an on demand heater, if you restrict the flow of hot water then the water just gets heated more.

If you have unstable pressure then the best way to have constant water temperature is to have a full tank of water at the temperature you want. There is nothing that can upset that.
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Offline james_s

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Re: Electric shower, anything I can do?
« Reply #8 on: July 23, 2019, 09:40:08 pm »
I take it you are dealing with an "on demand" heater which heats the water as it goes by? In America they also call them "tankless".

I have a natural gas tankless heater and they are crap. You cannot enjoy a shower with stable temperature. And if your pressure and flow are not stable it makes the situation so much worse.

In my second home I have a big tank heater and it is much better. And you can even fit a thermostatic valve and temperature stability will be rock solid.

For a good shower you want a good tank of hot water. It does not need to be very hot, just 40 or 45ÂșC will do so you only need to mix very little cold water. Excessively hot water temperature is dangerous and should be avoided.



Tankless water heaters are great *if* the whole system is designed around one and everything is sized properly. The problems usually occur when one is retrofitted into an existing home that was plumbed to use a conventional water tank, or when the system is designed with less care than necessary. With a small household a conventional tank is fine, but for a medium sized family it can be a struggle not to run out of hot water frequently when you have people showering, doing laundry, washing dishes, etc. Both conventional tank and tankless systems have advantages and disadvantages but I don't think it's fair to call one whole category crap.
 

Offline soldar

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Re: Electric shower, anything I can do?
« Reply #9 on: July 23, 2019, 10:06:51 pm »
Both conventional tank and tankless systems have advantages and disadvantages but I don't think it's fair to call one whole category crap.
Oh, I agree. But a big tank of water is much more forgiving and will generally provide more stable temperature regulation.

Providing stable temperature regulation with an on demand heater is much more complex because you need a feedback system that adjusts the power input in order to maintain a stable temperature. You can have an electric power control so that the water temperature remains stable. With a gas heater it can be done only within certain margins and is much more complicated.

On demand heaters have the advantage of not needing a tank (which takes space) and not needing to maintain the temperature of the tank so there can be a savings in energy.

On the whole I prefer a tank of water at a temperature very slightly higher than needed at the point of use. It is difficult to beat that for temperature stability and for simplicity.

If you need lots of water, more than a tank can hold, you could place a on-demand heater in front of the tank and that way the tank provides a big temperature buffer.
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Online SiliconWizard

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Re: Electric shower, anything I can do?
« Reply #10 on: July 23, 2019, 10:58:22 pm »
I think Electroboom made a video about electric showers. ;D
 

Offline james_s

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Re: Electric shower, anything I can do?
« Reply #11 on: July 23, 2019, 11:51:06 pm »
I have a conventional tank which I have set quite hot as the hot water is nice for washing dishes and things and mixing it with cool water at the point of use allows a modestly sized tank to go a lot further. Definitely downsides to this too though, it's a safety issue for kids (which I don't have) and it's harder on the tank. Temperature surges were once an issue but when I redid the bathroom I installed one of those valves that regulates the differential pressure and that has worked very well.
 

Offline NiHaoMike

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Re: Electric shower, anything I can do?
« Reply #12 on: July 24, 2019, 01:02:04 am »
Try putting a diode in series with the heater?
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Offline paulcaTopic starter

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Re: Electric shower, anything I can do?
« Reply #13 on: July 24, 2019, 06:53:46 am »
Yes, sorry, forgot the international audience.

The shower is a wall fitted unit that takes cold water in, has 9Kw of heating elements, and hot water comes out of the shower head.  It's on it's own circuit with a current breaker and RCD.  So if the water ever conducts it will, hopefully conduct to earth and trip the RCD.  Remember it's 240V, so 9Kw is circa 37 amps.  Usually these are wired with 10mm twin and earth cable.

The house is old, built 1968.  It has an unpressurized, vented hot water system with a cistern in the attic keeping it full.  So both the cold and hot water are gravity fed upstairs.  The shower runs off the cold and apparently, according to a plumber has a priority valve trying to insure it gets the water pressure if other taps are turned on.  This makes the water pressure really poor even when the shower is off.

The temperature control seems to just change the water flow rate to alter the temperature.  So when I say "minimum" I mean minimum setting for temperature which equates to maximum flow rate.

The comment about winter temps is an interesting one as "Big Clive", during dismantling one reported the "Low" setting was for "summer" when the tap water is a few degrees warmer.  So maybe, it will just be a bit like it is now for the next few months and when the mains water (and the water sitting in the warm attic) cools down it will be fine.

The heating system is oil fired central heating with an heat exchanger coil in the "hot tank" in a cupboard upstairs.  There is even less pressure from it.  In fact the shower attachment on the normal hot tap won't even flow when you lift it up to showering height, it literally stops.

The heating upgrade is basically to modernize the system.  Modern systems that are being installed around here are natural gas (utility fed from the street, used to be known as "town gas" when it was made from coal) boilers and a mains pressurised system, so the attic cistern comes out and the whole central heating and hot water system is fed from a mains water inlet.  So around here that's about 2-3 bar (I think).  It's going to cost me about ÂŁ3000 but ÂŁ2400 of that is interest free credit for a year.
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Offline MosherIV

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Re: Electric shower, anything I can do?
« Reply #14 on: July 24, 2019, 07:14:10 am »
If I understand the plumbing correctly, the electric shower is fed from a water tank in the loft  :palm:

Try connecting the electric shower to mains water, run the water in let up to the electric shower heater. Most electric showers are designed to be run from mains water.

Modern house plumbing no longer use a tank in the loft. The whole house is run off mains water.
 

Offline paulcaTopic starter

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Re: Electric shower, anything I can do?
« Reply #15 on: July 24, 2019, 08:21:05 am »
If I understand the plumbing correctly, the electric shower is fed from a water tank in the loft  :palm:

Try connecting the electric shower to mains water, run the water in let up to the electric shower heater. Most electric showers are designed to be run from mains water.

Modern house plumbing no longer use a tank in the loft. The whole house is run off mains water.

I'm aware of this, but the house has not (yet) been modernised.  I am "assuming" it is run from the header tank in the loft as that's normal for a system of this age.

So I'm resigning myself to put up with it until I can re-do the heating as a pressurized mains fed system.  That's possible to get done this autumn as apparently it should only take 2 days to complete. 

On a related note the choice has been presented to me as to whether I want a "Combi" set up or a "System" setup.  The former has no hot tank and water is heated on demand by the gas boiler.  I have had this before and it's awesome; turn on a tap and you have scalding hot water in about 20 seconds.  However the downside is, I have no hot tank and cannot later take advantage of solar PV water heating.  It also has a more invasive and expensive install as the hot water tap circuit needs replumbed to the boiler.  Going the system approach I have a heat exchanger in the hot tank so the gas can heat it, but I can put a DC immersion in the tank at a later time and as long as I can control the hot water/heating circuit valve and the circulation pump I will save on gas for heating not just the water but the radiators too.  Of course 1kW of solar will not go that far, but it will heat the to tank to 60*C fairly easily during the day.
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Offline soldar

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Re: Electric shower, anything I can do?
« Reply #16 on: July 24, 2019, 09:51:05 am »
I have designed and modified a few domestic hot water systems of very different nature. My boat, homes with on-demand heaters and homes with tanks. Depending on your aim and needs some may work better than others and all can be made to work relatively well if you make it expensive and complicated enough.

Domestic hot water systems are not complicated to understand for anybody who has the ability to understand electronic circuits and can be modeled very similarly.

On-demand systems intrinsically suck at maintaining water temperature because basically they dump a fixed amount of energy into the water and any change in any parameter will result in a change in temperature. So you need to be able to modulate the energy and have a feedback loop that measures output temperature and modulates energy accordingly. This is possible and is done but adds initial expense and complication and risk of problems and failures.

One advantage of tankless systems is you save a little space but that makes sense only if you have the tiniest of apartments. Another advantage for systems with very little use is you are not maintaining a tank full of hot water which means losses that need to be replaced.

But, on the whole, by and large, a tank system is going to provide better results, better water temperature stability at lower initial cost.

I have seen homes in England with both gas heaters and electric on demand heater. I never understood it. It seems salespeople sell stuff and homeowners buy stuff they don't really need because they do not understand the problem or the system.

If you want to have an electric on-demand water heater and you require stable temperature then there is only one thing to do which is to modulate electric power with a feedback loop that measures output water temperature. And studying the system it will have certain limits, an envelope of pressures, flows, input temperatures, etc.  This is what gas heaters do and they are incredibly complicated and expensive.

Right now water arrives from the mains quite warm and needs very little warming up for a shower but my on-demand heater cannot provide so little heat. It is below the minimum it can do even at the minimum setting. A solution which works but might not be obvious to non tech people is to open the sink hot water and dump some hot water that way. Dump half or 3/4 of scalding water down the drain and use 1/4 in the shower mixed with cold water. Not very energy efficient but with a gas heater there is not much else you can do.

With an electric heater it is trivial to insert a triac power control and regulate the temperature manually but it is better to sense the temperature automatically as it leaves the heater and insert a small tank or long pipe to stabilize any fluctuations.

But, yes, I have seen plumbing and water heating systems in the UK that are hard to understand for anyone with a bit of understanding. I think it may be a combination of patching very old systems and not really understanding how things work.

For a while I was staying in China in an apartment with a gas on-demand water heater which was impossible to get a decent temperature. The water was either scalding or boiling. I very soon learned to use two low stools. Put a tub on one and mix hot and cold water until I got the desired temperature. Then sit on the other stool and use a mug to shower water from the tub over myself. Works pretty well and saves a lot of water.

I was doing the same thing on my boat until I fixed the system which has its own complications, including cycling pumps.


« Last Edit: July 24, 2019, 09:56:03 am by soldar »
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Offline alanb

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Re: Electric shower, anything I can do?
« Reply #17 on: July 24, 2019, 09:59:05 am »

I'm planning on upgrading the whole heating system to a pressurized setup, so this is a temporary problem, but an annoying one!

Put your efforts into upgrading the whole heating system. This annoyance is a great incentive to upgrade as soon as possible.
 

Offline stevelup

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Re: Electric shower, anything I can do?
« Reply #18 on: July 24, 2019, 11:40:07 am »
You can get better electric showers - one example is the Mira Advance - this is thermostatically controlled and modulates the heater. Means the temperature is unaffected by water pressure.

Have a look at Triton as well - they do about half a dozen different thermostatically controlled ones.

Triton also do one with a pump. So if your current one is fed from a loft tank rather than the mains, you could go for that.

But to be honest, as has already been said, electric showers are a bit crappy anyway. Is there no way you can get a proper hot+cold feed to the location. The only advantage with putting another electric one in would be simplicity of installation.
« Last Edit: July 24, 2019, 11:45:24 am by stevelup »
 

Offline richard.cs

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Re: Electric shower, anything I can do?
« Reply #19 on: July 24, 2019, 12:08:18 pm »
I am "assuming" it is run from the header tank in the loft as that's normal for a system of this age.
You should check that assumption. This kind of shower is essentially unusable on a header tank and I've never seen one plumbed that way. Even in houses with header tanks they usually tee off the rising cold before it goes into the tank, otherwise they just don't work at all, in most cases refusing to turn on due to low pressure. If it really is on the header tank then rearranging the plumbing is step 0 but I suspect as it sort of works you'll find it is on mains pressure just your mains pressure is crap.

As you describe it you essentially have too big a gap between high and low, you need a "medium" which many of these showers have but not yours. It's probably one element or both with the two of similar power, better ones either have 3 elements or two dissimilar ones to give three power settings e.g. 3 kW, 6 kW and 6+3 kW. You may be able to create a medium setting of 1.5 elements by putting a diode in series with one of them, you'd then have cold, low and medium rather than cold low and high.

They usually have a mechanical pressure regulator up front to take out the worst of the variation when someone uses water elsewhere in the house, and you'll find that changing settings between summer and winter is necessary. Some of the fancy modern ones do active temperature control by varying the input power rather than having a valve to restrict the water flow. Buying one of those or much cheaper buying a 3-step basic one would probably fix your problem, but any electric shower really needs connecting to mains pressure water.

As a side note, be careful with your decision to go with a pressurised system and presumably a combi boiler (instant gas water heating combined with central heating for the international audience). They have a number of disadvantages over a well designed low pressure system with storage and these are often skimmed over by installers wanting to sell the shiny and new.
 

Offline paulcaTopic starter

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Re: Electric shower, anything I can do?
« Reply #20 on: July 24, 2019, 12:53:33 pm »
I have seen homes in England with both gas heaters and electric on demand heater. I never understood it. It seems salespeople sell stuff and homeowners buy stuff they don't really need because they do not understand the problem or the system.


With an electric heater it is trivial to insert a triac power control and regulate the temperature manually but it is better to sense the temperature automatically as it leaves the heater and insert a small tank or long pipe to stabilize any fluctuations.


For a while I was staying in China in an apartment with a gas on-demand water heater which was impossible to get a decent temperature. The water was either scalding or boiling. I very soon learned to use two low stools. Put a tub on one and mix hot and cold water until I got the desired temperature. Then sit on the other stool and use a mug to shower water from the tub over myself. Works pretty well and saves a lot of water.

I was doing the same thing on my boat until I fixed the system which has its own complications, including cycling pumps.

Interesting comments.  A few of them, from my experience...

Having an on-demand electric water heater is common in most UK households with a hot tank.  It's simply because you might not want to put the heat on in summer.  Might be a surprise but none of the houses I have lived with a hot tank have had the ability to select "Hot water only" for the boiler.  So in summer you simply wouldn't use the heating to get hot water as that would heat the house radiators too.

The on-demand heater, usually referred to locally as "The immersion heater" and often a switch or pull cord in the kitchen is a 13A or 30A immersion heater.  However it's not just an element stuck at the bottom of the hot tank.  It takes water out of the bottom, heats it through a coil and via convection dumps it into the top of the tank where it will stay, heating the water from the top down.  The hotwater outlet is designed to take water from the top of the tank if available.  In my house if the water is cold because the heating has been off, the "immersion heater" will have it hot enough to scald your hands in about 1 minute.   Obviously if you try and run a bath with that or have a shower it will use up the layer of hot water rapidly and it will run cold.  You can heat the whole tank with the immersion heater but it would be wasteful.

This issue is why people put electric showers in.  It's so that they don't need to rely on running the heating in summer or using the immersion. 

Yes systems do exist with an electrical operated valve to select "Hot water", "Radiators" or "Both" but they are very rare here.

A triac on a 7Kw water heater will never get past UK electrical codes.  I expect it will be, large, noisy, expensive and likely to melt or go on fire at some point.

Hot water in the UK comes out of the tap as hot as you can legally make it.  The 65*C target is very often breached by gas boilers and electric water heaters.  My previous apartment would happily produce water close to 80*C.  You could almost make tea or coffee with it.  All most all taps in UK homes are mixer taps.  This is a rather recent thing as there are regulations stating that the hot and cold taps be separate anywhere the hot tank is coming from a header tank system as it can potentially contain stagnant water.  This regulation has become lax however and many people fit mixer taps in the bathroom regardless of the regs. 

So you can expect the hot water to be absolutely scalding and expect to have to mix cold with it to get a temperature for bathing.
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Offline stevelup

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Re: Electric shower, anything I can do?
« Reply #21 on: July 24, 2019, 12:56:01 pm »
You say very rare, I say I have -never- seen a house without independent control over heating and hot water!
 
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Offline paulcaTopic starter

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Re: Electric shower, anything I can do?
« Reply #22 on: July 24, 2019, 01:04:14 pm »
As a side note, be careful with your decision to go with a pressurised system and presumably a combi boiler (instant gas water heating combined with central heating for the international audience). They have a number of disadvantages over a well designed low pressure system with storage and these are often skimmed over by installers wanting to sell the shiny and new.

Can you elaborate a little?

I was considering going for the System boiler approach which has just a hot water circuit flowing through the heat exchanger coil in the hot tank, which, assuming I fit an electrical routing valve giving me control of hot water only, radiators only and both gives me the best of all worlds.

The main difference is that this system runs at mains pressure, so as soon as you pull water out of the hot tank it is replaced by the cold mains inlet.
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Offline richard.cs

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Re: Electric shower, anything I can do?
« Reply #23 on: July 24, 2019, 01:12:13 pm »
You say very rare, I say I have -never- seen a house without independent control over heating and hot water!
Agreed, I've not seen one either. A choice between hot water only, or hot water and heating together is very common, i.e. many UK systems can't do heating without hot water but most can do hot water without heating. It doesn't even need an extra valve, many of them rely on gravity circulation for the hot water (boiler on, water tank gets hot) and a pump to circulate the heating water (boiler and pump on, hot water and radiators get hot).
 

Offline paulcaTopic starter

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Re: Electric shower, anything I can do?
« Reply #24 on: July 24, 2019, 01:19:09 pm »
You say very rare, I say I have -never- seen a house without independent control over heating and hot water!
Agreed, I've not seen one either. A choice between hot water only, or hot water and heating together is very common, i.e. many UK systems can't do heating without hot water but most can do hot water without heating. It doesn't even need an extra valve, many of them rely on gravity circulation for the hot water (boiler on, water tank gets hot) and a pump to circulate the heating water (boiler and pump on, hot water and radiators get hot).

Is this a mainland thing?  I have lived in about 5 different places in Northern Ireland with vented/pumped heating systems and there has only ever been one control, heating on, heating off.  If it's on, you get both hotwater and radiators, if it's off you get neither.

The coal fired system "did" have a circulation pump control, a spur switch on the wall.  However that didn't have any effect on the heating/hot water it just sped the process up instead of it relying on convection alone.
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