We have a Wilo Pico pump and when set to the ‘sweet spot’ is very quiet; I’m going to suggest that the problem may be with one of the radiator valves nearby. Has the system been balanced properly? (All TRV’s fully open and the lockshield valves gradually closed until the output of the individual radiators match the needs of the rooms.) [Please see

https://renewableheatinghub.co.uk/how-to-balance-radiators-the-role-of-the-lockshield-valve

for further enlightenment]

Are you using thermostatic radiator valves? A TRV can easily sit at just the wrong degree of closure and will ‘sing; until the conditions such as temperature change. The flow rate changing will influence the noise emanating from a TRV sometimes. I’m sure others will also have ideas for you. Regards, Toodles.

@toodles thank you for your input. We balanced it ourselves as best we could, but will have another go at it. However it is worst in a bedroom with the radiator permanently off, and in a cloakroom at the opposite end of the bungalow with the radiator fully on!

@grumpidoc do you have glycol in your system if so you can deactivate the frost protection mode so the pumps won't activate at night.

We do, tho I would need to check if the concentration is sufficient.

If we did that in this freezing weather would that mean the cooling fins on the outside unit would ice up?

And further question, sorry for my ignorance, I am aware turning it off overnight will make the heat pump work harder next morning when it's turned back on and that although that will reduce its efficiency it might not increase the total energy use, but would doing that regularly shorten the life of the ASHP?

Thanks

Although the primary pump installed on my EcoDan is not the same make as yours I had a similar issue - mostly solved by reducing the flow rate. The highest flow rate was not that much louder but it also created two frequencies that made the noise very unpleasant. It certainly seemed that one of other these penetrated the walls more readily and I was very aware if it at first - but that may diminish with time.

I hope your Wilco is more energy-efficient that the pump I have which has a box of electronics that gets stupidly hot. If your pump remains physically cool you could consider trying to muffle it.

The frost protection mode is about preventing pockets of water freezing and damaging the pipes. If you have glycol in the system then this is not a problem, so the protection mode is not required to run. If you have water only then you should know by the presence of anti-freeze valves on the external pipes close to the outdoor unit – the frost protection mode simply circulates the warm water in the insulated pipes to prevent these cold spots from building up. Icing of the fins is a cosequence of cold damp air when the HP fan is actually running.

Like many people I have two degree setback overnight and I think it may be better overall. Any setback effectively turns the pump off for a period of time, the entire length of the setback unless it is cold and the lower setting is reached during that period. The return to daytime temp is staggered so the algorithm is not set the problem of raising the house by two degrees at once which would cause it to work harder.

At temperatures when the pump is cycling rather than generating heat continuously, having this setback means that instead of cycling for six hours to maintain a consistent temp the pump works a bit harder but continuously for three or four, and that continuous run period is inherently more efficient.

Posted by: @grumpidoc

↑

which usually means no further heating is required till morning so it's really the frost cycle that causes the problem.

From your quote here I understood that the heat pump wasn't operating at night as you have the house quite cool.  In the documentation you got from your installer it should state the temperature the glycol concentration was set at to protect, mine was -8C so depending on where you located its likely to be sufficient to turn it off completely.

Posted by: @grumpidoc

↑

And further question, sorry for my ignorance, I am aware turning it off overnight will make the heat pump work harder next morning when it's turned back on and that although that will reduce its efficiency it might not increase the total energy use, but would doing that regularly shorten the life of the ASHP?

It won't work any harder than is currently does it will come on when your thermostat calls for heat you aren't changing that, as Harriup said icing only occurs when its running, cycling on and off multiple times an hour will shorten life of the compressor thats not the case here.

As mentioned pump speed could be a cause, if you go into service settings when the heat pump is running the heating and find the running information menu and input code 540 the number that comes on the screen is your flow rate in L/min for an 8.5KW Ecodan the recommended flow rate is 15.2L/min.  If the flow rate is greater than that then you can turn it down.  If you have an ecodan preplumbed cylinder this should be controlled from the main controller, in the same service menu go to pump speed and see what it is set at values are 1-5.  Change it down a value and go back to the running information menu, code 540 and check what the new value is. Repeat until you are close to 15L/min.  I find a setting of 2 gives me 14L/min and the best compromise between performance and noise.

Thank you @harriup and @gary this is all very helpful. The paperwork just states a rust inhibitor and 'antifreeze' and it looks like we have an anti-freeze valve. We've contacted the installers about the noise and they're checking with their tech team but if they don't have any other solution we'll talk to them both about adding glycol (can it be done after installation??)and about pump speed settings. They've been very responsive so we want to await their reply before doing anything.

We're working on balancing the radiators but it'll need to wait till it's not quite so cold to do it properly. All the radiators now have TRVs fully open and flow is controlled by the lockshield valves (we don't have an issue with solar gain etc in the winter!) The guide referenced by @toodles is really helpful.

Thank you all for helping! I'll update when we're sorted.

@grumpidoc I would still go into the menu when its running and check what the pump speed is set to and what the flow rate is, then you will have that info and know if you can turn it down.  A lot of installers will set it at max and walk away.