need help getting a capacitor replacement.

[Jwillis]

Inductors (your motor) lag current in relation to voltage and capacitors lead current in relation to voltage. This is phase shifting of the current in relation to the voltage. 
To low or to high a capacitor value will shift the phase of the  current to much and will cause hesitation in the motor. You described that hesitation in your opening post.
It will also cause current consumption of the motor to rise because the field can't "build" properly . This creates heat in the motor and can be destructive to the motor  The rise in current consumption can also trip breakers.
You can test with an Ohm meter but will only tell you that its shorted or not. If the resistance rises to infinite then the cap is charging off your DMM.
But it won't tell you its charging enough. All capacitors will show an open circuit when fully charged. even weak ones.
Your DMM you described has a capacitor test setting. Use that but discharge capacitor before testing. The reading should be close enough to indicate if the value is within exceptable tolerance.

[james_s]

An ESR meter is the best way I've found to test capacitors. You could connect an AC voltage to a capacitor and measure the reactive current that it draws. Really though the easiest test is just swapping in a known good capacitor and seeing if that fixes the problem. Motor run capacitors do fail often, and in my experience by the time I noticed something was wrong, the capacitor was completely open circuit.

[Gyro]

At the end of the day, if it isn't the cap then the pump is trashed anyway, so it becomes a little academic (especially as  the OP has already ordered a replacement cap).

Just a couple of warnings on the pump itself. Don't let it spin dry, it has water lubricated (chrome plated) sleeve bearings. These will get torn up very quickly if there is no water to lubricate them, causing excessive clearance and noisy running. Re-fit, fill and bleed the air out of the inner housing (rotor + bearings) through the screw cap at the far end before running it.

[floobydust]

There will be a thermal cutoff fuse embedded in the stator windings. Hopefully OP verified resistance with an ohmmeter, that it (windings) are not open - before thinking it's the run cap...

[james_s]

It's usually not embedded, it's at the surface on one of the ends. I've had to replace two of those recently in small motors, in both cases the thermal fuses failed around the same time with no signs of overheating, I'm wondering if there was a power glitch that popped them. Those were both shaded pole fan motors though, I don't think larger motors typically have thermal fuses.

[floobydust]

I would say it kind of depends on the fluid temperature, the Grundfos can be pumping quite hot water which leaves not much margin I think for the thermal cutoff's trip point.
For hydronics water temp of say 180ºF /80ºC (typical here on cold winter nights -25ºC) and the wire's enamel varnish 250ºF/125ºC limit, as a guess. The motor's temperature rise is unknown.

As long as OP did check for continuity on the windings as well as the cap's value.

[kato1144]

So the replacement parts have come in and I'm going to try and do the repair now, so I read some of the post over the past days and first of all I did test that the pump still works when I pulled it out of the housing (it still had water in the space between the impeller and winding's) if I powered the pump and pushed the impeller and it spun up so I was pretty sure it was a bad capacitor. With that said I did do a resistance reading across the power wires and got a reading of 43ohms exactly, I did plop that in to a “winding's calculator” on line and it was not giving me the answers I hoped for, either my pump need 2.67amps (0.74 rated) or my resistance should be 155.4ohms https://calculator.academy/motor-winding-resistance-calculator/

is more then possible that I'm missing something to do with this calculator so I'm going to push on with the repair, I will try and test the old cap and new, see if I can determine the failure for certain.

Just want to add the pump was quite hot when I found it a failed, it was on demeaned for almost a whole day before I noticed I had no domestic hot water (at least 12hrs) of power with no active cooling, the water was turning to steam a bit in the housing but it was not extremely hot, like, it was certainly around 70oC to 90oC I think, I was able to handle the pump with my hands about 20 seconds after I cut power, so I think/hope that the water convection was enough to keep the pump from burning up by sinking that heat, I have seen these pumps have a flow failure (air lock) for days and survive to pump again so here is hoping.

Lastly the replacement cap it almost 1:1 for dimensions so it's going to fit good atleast

[kato1144]

well bad news, tried the pump back in to the housing, purged the air, applied power and nothing, the pump became warm that's it, pulled apart I could still spin it up with my finger pushing it in the right direction, it does feel weak until it get up to speed then it spins normally. When I was re-installing the backup pump I checked the resistance across the power leads and got a reading of 44.5ish ohms so the winding's on the problem pump are ok by comparison. Finally I found a capacitance tester on my multi-meter, im not sure how accurate it is but I did a test on the new cap and got a reading of 10uf and on the old cap was a result of 10.5uf so not sure if that mean the old cap is good or there is more to testing these caps then a uf reading, also I took a resistance reading of the wires that the cap attaches too and got wild reading from 2.223m ohms to 0.667m ohms. The ohms reduced over time so not sure if any of that is right, let me know what you think, should I dig in to the pump further let me know.

BTW the impeller spins freely, not greased bearing freely but certainly on par with any hydronic pump impeller I have come across

[floobydust]

That's a bummer, hoped it would be a straightforward fix. If you can post pictures, I can't find any wiring diagrams for the pump.
The motor has two windings, I would check both with an ohmmeter and compare, and it has a thermal fuse and the cap. Perhaps like this drawing. It's pretty low power motor.
BUT I did see a UPS 15 (different model, 3-speed) with a starter module. A diode+starter heater switch (or PTC?) that goes across the cap wires as the black thing. Do you have one?

The lead's resistance varying 2.223m ohms to 0.667m ohms is that milli or mega.

[james_s]

The multimeter will test the capacitance but that only tells you part of the story, it can't test ESR or leakage at the working voltage and that is a much better indication of the health of the capacitor.

The fact that the pump still doesn't run is not a good sign though. Are you sure the new capacitor is wired properly?

[kato1144]

Thanks floobydust, my pump is a single speed and there is no thermal fuse as far as I can tell, and i do belive it was Mega ohms, i will re-check when I dig back in to it.

james_s maybe i should look in to a cheap ESR tester, but ya the old cap and new cap did not have polarity as far as I could tell, maybe I did wire it in wrong but I have also wondered if maybe there is an issue with the connections internally where the cap wiring is connected, if that reading was 2mega ohms that might indicate extreme resistance, maybe there is a component like a resistor that is damaged or just a faulty connections. The issue is there is no clear way to get to the connections due to the water resistant design for the internal connections, I fear to get to them would be destructive.

I have some pics of my repair, take a look tell if you see a glaring issue with anything, maybe I made a mistake and fail to see it.

[Gyro]

I'm sorry to hear that this hasn't been a successful repair.  I was thinking that another wire (insulated) ended capacitor would be the preferred solution but, looking at the photos, it's not obvious how the existing capacitor wires are terminated, so joining to the existing ones actually looks easier.

The method of attachment to the existing wires looks good, however in the 3rd photo, do I see exposed wire poking throught the heatshrink (right hand end)? I can't work out whether it's chewed insulation or whether it is the metal bracket behind, maybe contacting the cover.

As previously mention by floobydust, the 200V DC rating (140V AC) sticks out in sharp focus. I must admit that I didn't spot it when you listed all of the Mouser part numbers. Even so, these film capacitors have a fair amount of contingency factor (tested at 200% voltage), so I wouldn't have expected it not to work at all, even if life might be shortened.

I don't know if it is possible to check the original capacitor lead connections to the motor? They just seem to disappear down into the rubber / plastic block on the motor.

[floobydust]

The motor has two windings, MAIN and AUX. I would check resistance across each- the white pair, and the brown pair. To see if a winding went open-circuit- which it looks like if you're getting megaohm readings. The winding or a thermal fuse popped maybe. A winding should be below a few hundred ohms I'd guess.
I can't find detailed info on the Grundfos pump wiring UP 15 documents show nothing but the usual marketing and install blurbs.

Sometimes Grundfos hides stuff in the connector to the motor. So it looks like 4 wires going in but pump motors have in the black moulding a white connector with many more pins (6-8) on the other side.

Careful the cap can hold a stray charge and bite hard, so always measure DCV across it when power is off to ensure it's discharged.
Grundfos replacement capacitor "terminal strip and capacitor" UP 15 is 595424. Some pics of 595426 show a starter across the cap. It looks like they added the motor start switch to newer UP 15 designs?

If it's the motor winding, I'd phone Grundfos and ask what the repair options are.