Hi Brian. Welcome to the forums.

Firstly, well done for taking the plunge with a heat pump. From the way you’ve described the property, it actually sounds like the sort of building that should suit a heat pump very well with good insulation, underfloor heating and generally a well thought-out approach to energy and water use.

You’re also absolutely right… the hardware is only part of the story. A good heat pump installed poorly can perform badly, while a well-designed system with the right hydraulics, controls and commissioning can be excellent. Unfortunately a lot of the issues people experience come down to the installation and system setup rather than the machine itself. 

Having said that you’ve definitely come to the right place. There’s a lot of collective experience on this forum and people are generally very good at helping diagnose problems if you can share a bit of detail about the system.

When you post your question(s) include things like the make and model of the heat pump, system layout (buffers, cylinders, pipework), emitter types and any error messages or symptoms you’re seeing. Photos of the plant room are helpful too.

Don’t worry about your level of technical experience… everyone starts somewhere, and many members here began exactly where you are now.

When the heating is on, whether or not the outside heat pump is working (spinning) or not, we have a constant humming in the rooms. Its most noticeable at night times, when everything is quiet outside and around the house. Ive tried just having the radiators on, radiators on and underfloor heating (UFH) and UFH just on....it still hums. It only stops when we activate the Domestic Hot Water (DHW) cycle (Cosmo unmixed pump group DN 25 stops for the heating) and instantly the humming stops. We have taken to going to bed early as the humming isnt as bad upstairs.

We have lived in this house with a nearly 3 decades old Gas boiler (before swapping for the ASHP) and never had any hummimg ever.

Here is a  video of the humming that is being transfered throughout the house. 

please, please, please can someone help me?

Many thanks,

Brian (going slightly out of my mind)

@expatingermany Sounds to me as though you have a pump running and the water gushing through the pipes is transmitting it around the system and fabric of the walls. Perhaps that pumps stops running when DHW heating happens or it relieves the strain on the pump. Regards, Toodles.

Hi Brian. When in hot water mode the noise stops as its most likely wired so the heating pumps turn off during hot water cycle. The system does look a little over engineered, if the majority is UFH then why the mixing valve? could the radiators not have been sized so the whole system is open loop, and weather compensated at the same temperature. That way you'd not need to other pumps and possibly not the buffer tank either? Worth asking the installer about this.

I think the above posts are spot on, the noise is most likely the 'secondary' pump which could reasonably be designed out.  Alternatively I have heard people say that wilo pumps are quieter than grundfoss these days, but dont know if thats true.

You could look for the pump and see if touching it or surrounding pipework makes a difference, sometimes its something quite simple

Also is your system operating open loop, ie all zone valves and TRVs permanently open, not opening/closing under thermostat control.  It could be that.

Posted by: @expatingermany

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When the heating is on, whether or not the outside heat pump is working (spinning) or not, we have a constant humming in the rooms. Its most noticeable at night times, when everything is quiet outside and around the house. Ive tried just having the radiators on, radiators on and underfloor heating (UFH) and UFH just on....it still hums. It only stops when we activate the Domestic Hot Water (DHW) cycle (Cosmo unmixed pump group DN 25 stops for the heating) and instantly the humming stops. We have taken to going to bed early as the humming isnt as bad upstairs.

We have lived in this house with a nearly 3 decades old Gas boiler (before swapping for the ASHP) and never had any hummimg ever.

Here is a  video of the humming that is being transfered throughout the house. 

please, please, please can someone help me?

Many thanks,

Brian (going slightly out of my mind)

This sounds very similar to my system where recently we had the 'secondary' pump electrically disconnected and the 'onboard' pump speed cut by around 50% (tuned). Check system flowrate compared to ASHP spec sheet. The differing pump speeds were combining to create 'issues' which invoked the noise. System is now working well and 'silently'

Posted by: @giganto

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This sounds very similar to my system where recently we had the 'secondary' pump electrically disconnected and the 'onboard' pump speed cut by around 50% (tuned). Check system flowrate compared to ASHP spec sheet. The differing pump speeds were combining to create 'issues' which invoked the noise. System is now working well and 'silently'

Thats not going to work if you have a buffer, low loss header or plate heat exchanger between heat pump and emitters, unless you also remove the intervening component so they are directly connected

@expatingermany 
I do not have the knowledge of the people who are participated here, could perhaps the below post be of use to you?

https://renewableheatinghub.co.uk/forums/postid/60048/

Dry rotor circulators are noisy, but wet rotor circulators are supposed to be almost completely silent.

I have a Grundfos Alpha 1L which is perfectly silent. Also a Wilo Yonos Pico circulator that makes the same kind of noise, a kind of high pitched motor whine. It didn't do it when it was new. Once the heating season ends, I'll open it and clean it, could be some dirt stuck in the impeller, or maybe a dead bearing. Depending on the model, some parts can be replaced without buying a whole new pump.

@expatingermany your pump sounds a bit like my Mum’s (gas) system when there was air in it. You might get some relief by bleeding the highest radiator.

Is the flooring surface on your ufh suitable for the same temperature throughout? If so you (your plumber) can dispense with the extra pump possibly.