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Help me keep the faith with my air source heat pump installation

AdamK · 2025-03-29T13:05:20Z

i knew when setting out on this road it would be a challenge i just didnt know how much of one it would be. after having many quotes some i couldnt fathom why they were so high i thought id sorted an installer. problem is they are 72miles away so first issue was doing a remote heat loss which has been back and forth several times to get it more or less correct, but still have one room thats 2m2 smaller than what i measured. anyway the next issue was getting the 28mm primaries in before the new kitchen ceiling goes in. they sent a plumber that proceeded to bugger the job up as the wall sleeve kit hadnt been supplied to him. so sent him on his way. was promised the sleeve kit the next day and i said my plumber could fit it to save them sending an engineer. next day no kit. add to this all the mods im having to do to pipe work to maximise efficiency and im seeing why the take up is tiny in the UK. im not naming the company as they are a recommended one and have apparently done good work else where but maybe thats in there local area. i know living in Boston creates its own issues being miles from any proper trades so if someone asked me would i recommend getting a heat pump in my area id have to say no. theres just not enough skilled trades where i live.

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Air Source Heat Pumps (ASHPs)

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AdamK

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Topic starter 08/02/2026 2:41 am

Got Vaillant coming on Monday. Any tips on how to get them to sort the sensors and humming sound in the house?

This post was modified 2 weeks ago by AdamK

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JamesPa

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08/02/2026 11:07 am

Posted by: @adamk

↑

Got Vaillant coming on Monday. Any tips on how to get them to sort the sensors and humming sound in the house?

Sorting the sensors - get them to swap them round or put both on the same pipe to demonstrate that they are matched, otherwise they will probably put in two new equally random sensors. Note the mismatch and which way round they go for future reference

Humming - make sure you know what triggers it so that the conditions can be created when they are present. Otherwise sods law guarantees there will be no humming when they come.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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AdamK

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Topic starter 09/02/2026 6:29 pm

@jamespa

They came and after a bit of push back accepted my idea to put all 4 sensors in the same place indoors and wait for them to balance. Now have 2 that are within about 100ohms of each other. Couldn’t suggest a fix for the humming other than the installer should have used Vaillant flexis. Did say the installer could move the external pipe clamps which I think might also help.

What I’ve noticed is I’ve still got the 0.2c gap which I’m guessing is the wiring resistance possibly. I’m going to cover the sensors in some insulation to see if that helps. If not I’m assuming the sensors goto the main pcb box so might measure the resistance there. Why they don’t put some small trim pots or software adjustment on these I don’t know.

I did find out today that the sensors are exactly the same as the ones used on Vaillant boilers. As that’s what he had with him. You can remove them from the boiler clip and fit them to the heat pump clips.

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JamesPa

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09/02/2026 6:52 pm

Posted by: @adamk

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I did find out today that the sensors are exactly the same as the ones used on Vaillant boilers. As that’s what he had with him. You can remove them from the boiler clip and fit them to the heat pump clips.

I expect they are all made in the same factory in China!

Posted by: @adamk

↑

What I’ve noticed is I’ve still got the 0.2c gap which I’m guessing is the wiring resistance possibly. I’m going to cover the sensors in some insulation to see if that helps. If not I’m assuming the sensors goto the main pcb box so might measure the resistance there. Why they don’t put some small trim pots or software adjustment on these I don’t know.

I suspect because the absolute value doesn't matter to the day to day operation and they don't guarantee the accuracy of energy or COP readings, which is the only thing materially dependent on them being matched! Not entirely satisfactory I agree, it wouldn't be that difficult to calibrate them!

Posted by: @adamk

↑

Couldn’t suggest a fix for the humming other than the installer should have used Vaillant flexis. Did say the installer could move the external pipe clamps which I think might also help.

If there are no flexis then fitting them may well help. If he has just used third party ones then less likely. If you can find something that is vibrating in time with the hum that may give a clue of a point to either isolate or clamp!

This post was modified 2 weeks ago 2 times by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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AdamK

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Topic starter 10/02/2026 8:14 am

@jamespa the installer did fit primary pro flexis which aren’t that flexible. Because they had to move them as they were bending them which the manufacturer said was wrong they are being held by 3 per flexi wall clamps, I think just because those clamps were already there when it was solid pipe. So I plan to remove some so the flexis have more room to flex. Might help but not sure.

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