@cathoderay up until the last few days the rads have always had a very small detectable bit of residual warmth but as the outside weather is now getting warmer they are mostly cold to touch during the day until such time as the temp drops and the compressor kicks in.

Posted by: @painter26

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mostly cold to touch

25 degrees does feel cool/cold, remember blood temp is ~37 degrees. I think you may find your compressor is doing very long cycling to keep the output down. Can you read the leaving water temp from the Midea controller, it is on page 4 of the Operational Parameters (not page 3) as TW_O PLATE W-OUTLET TEMP (just to confuse us)? It should average at about 25 degrees. You could also keep and eye on total lifetime kWh use when the DHW is not on, and see if it increases. The compressor data on page 6 may also tell you something.

This is my heat pump on Sunday, before I turned the space heating off on Monday morning (yesterday morning). Note that during the middle of the day, when the OAT was above my right hand weather curve OAT set point of 15°, it is still running, with long cycling. The big spike at 1300 is my DHW heating.

Posted by: @painter26

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I could keep my settings as they are but even at night I get a lot of residual solar gain as the house is directly south facing so I would not need the space heating to kick in on a cold night 

For this reason as said before I would just turn it off.

@cathoderay I turned the room stat down to 12 degrees earlier this evening which, predictably, turned off the space heating.

Here's my controller now (I should correct my previous post with my current WCC parameters which are 45 flow temp at -4 OAT / 25 flow temp at 15 OAT):

@painter26 — that all makes sense. Space heating (the sun symbol in the middle panel) shows as off, and the leaving and returning water temperatures are the same, and low, at 17°C. Your space heating is off.

@cathoderay great, thank you.

Just bumping this up for @editor .

Are there any engineers local to Fleet in Hampshire who could advise on whether this is likely the expansion vessel that needs checking again after the new DHW tank was installed? I'm struggling to get any response from the original installer and I would like to resolve the trapped air issue and (very gradual) pressure loss.

@painter26 thanks for bumping this up. I'll circulate this to my professional/installer network to see who'd be available to look into this and help.

Thanks @editor 

@painter26 i am in Lightwater and midea trained. Sounds like a pretty straightforward issue but need to see for myself before recommending a plan/doing a fix

@painter26, Leading Renewable Change have just got in touch and said that if you call them on 01293 851 459, press service and speak with Ella, they can arrange to send out an engineer. I have no idea wha their charge out fee is.

Thank you!