Run it all day, lower the flow temp. Use less power and you'll get a constant heat all the time. You're letting it cool down and then it needs to get up to temp again. 

Thanks for the quick reply. I'm going to try running it 24/7 for a few days and then compare the temperature and energy use. I guess I'm wondering why the ASHP is barely ticking over, with minimal flow temp, when the house is cold?

@squonk do you have a heat curve on your system? Ideally you want it just ticking over, but maybe your heat curve needs tweaking for this time of year? I assume it's fine in the winter?

@batalto That’s something I’ve been wondering about. The Vaillant setup instructions says Heat Curve: Site Specific, it defaults to 1.00 so I haven’t changed it. There is also a setting for Adaptive Heat Curve, Vaillant says this should be Off, so that’s what I’ve done.

@squonk yeah you are going to want to change those, 100% you'll be on the wrong setting if it's on the defaults. I don't have your unit, but some people on here do. Try checking the role call to see who might be able to advise

Posted by: @squonk

Our Vaillant ASHP + UFH system takes forever to heat the house. Currently we run it from 0700 to 2200, with the thermostat set to 20 deg. Over the last few days it takes 8-9 hours to go from 17 deg to the required 20 deg. The floor heats up to about 23-24 deg, and the ASHP spends most of its time off. Flow temp runs about 25-30 most of the time. At least it’s not using too much electricity, but my house is cold. 

Any ideas for how to improve this? I guess I could run the system 24/7, or raise the flow temp (how?), or maybe something else? 

If you're using a third party thermostat with the ASHP's weather compensation, then the ASHP will only run when the room temp is below the thermostat target and the flow temp is below the weather compensation flow temp target corresponding to the outside temp. So when the WC flow temp target is reached the ASHP will stop heating even if the thermostat is still calling for heat.  It will only start again when the WC flow temp drops below its target. 

If this is what's happening then as a trial I would increase the weather compensation curve so that the target room is reached.  The thermostat will then stop calling for heat and the ASHP will switch off.  With a bit of tweaking you can come up with a weather comp curve that keeps your house at the right temperature whatever it is outside. 

In winter I have my thermostats set to 30 deg and I let the weather compensation control the house temperature.   

Posted by: @kev-m

If you're using a third party thermostat with the ASHP's weather compensation, then the ASHP will only run when the room temp is below the thermostat target and the flow temp is below the weather compensation flow temp target corresponding to the outside temp. So when the WC flow temp target is reached the ASHP will stop heating even if the thermostat is still calling for heat.  It will only start again when the WC flow temp drops below its target. 

If this is what's happening then as a trial I would increase the weather compensation curve so that the target room is reached.  The thermostat will then stop calling for heat and the ASHP will switch off.  With a bit of tweaking you can come up with a weather comp curve that keeps your house at the right temperature whatever it is outside. 

In winter I have my thermostats set to 30 deg and I let the weather compensation control the house temperature.   

 

The humble room stat, yet again showing how inappropriate it is for a modern heating system that uses compensating controls. It would be better for most people if the room stat was just replaced with an on/off switch 🤣

@squonk, ASHPs are designed to run 24/7 to get the most of out of the system in terms of efficiencies and comfort. To give you an idea, it’ll take our ASHP at least 24 hours to get our entire house to 21C when we turn it on for the first time in winter. It then just needs to run, doing its thing.

Posted by: @squonk

@batalto That’s something I’ve been wondering about. The Vaillant setup instructions says Heat Curve: Site Specific, it defaults to 1.00 so I haven’t changed it. There is also a setting for Adaptive Heat Curve, Vaillant says this should be Off, so that’s what I’ve done.

Installers don’t like to enable weather compensation because it’s a trial and error system which leads to multiple call outs, so they just set the system to one flow temperature.

My advice is for you to experiment with the heat curves to get it running optimally for your house and your personal comfort levels.

@witchcraft, have you conquered the weather compensation on your unit?

@editor There doesn’t seem to be any shaping to the curve, it mainly seems to control the relationship between inside and outside temperatures as far as I can see. If that is correct then presumably it’s a case of reducing it a step at a time and seeing what happens? Ie the lower the curve the more efficient the system is, so the ideal is to take it down to the point where the house doesn’t stay warm and then crank it up a little. Doesn’t seem very scientific, but maybe I’ve been overthinking the problem.