@derek-m I would assume it controls both, as there is little point running the ASHP and not the central heating pump and vice versa. The Nest will call for heat and turn on the central heating element of the ASHP which will then run in weather compensation mode.

I'll have to call the guy that put it in and ask him.

Hi Batalto,

The two pumps could actually operate independently, in that the pump located in the ASHP could run to heat up the water in the buffer store, and then the central heating pump could run, when the thermostat starts it, to move the warm water from the buffer store to the heat emitters.

Obviously, since the buffer store is relatively small in volume, both pumps would normally be operating at the same time.

I am not certain how your system is wired and configured, hence what may seem like stupid questions.

@derek-m I've emailed the guy who installed the system to ask

@kev-m, the problem is the hive, it is an expensive on-off switch. A TRV is useful to control the bedroom temperatures but must not be used anywhere else, all other radiators should have lock shields only. If you have 2 methods of controlling the room temperature, it is like having 2 bosses in an office, nothing gets done/heated correctly. (on-off thermostat, TRV, weather compensation, 3 bosses, you do not stand a chance)

Kev-n you are operating the system correctly, if all common radiators are open, the Mitsubishi thermostat communicates the internal temperature to the controller and automatically adjusts the weather compensation curve to maintain the set temperature.

@heacol,

thanks, all the rads have TRVs but they are fully open atm. I do have 2 zones though, bedrooms/inner hall and the rest (it's a bungalow).  

@kev-m You are probably getting reasonable performance then.

@heacol,thanks

Posted by: @heacol

@kev-m, the problem is the hive, it is an expensive on-off switch. A TRV is useful to control the bedroom temperatures but must not be used anywhere else, all other radiators should have lock shields only. If you have 2 methods of controlling the room temperature, it is like having 2 bosses in an office, nothing gets done/heated correctly. (on-off thermostat, TRV, weather compensation, 3 bosses, you do not stand a chance)

Kev-n you are operating the system correctly, if all common radiators are open, the Mitsubishi thermostat communicates the internal temperature to the controller and automatically adjusts the weather compensation curve to maintain the set temperature.

@heacool

The instal of my ASHP plus 12 radiators is due soon.  I thought I wanted ‘smart’ TRV’s on each.  As it is the installer intends to use dial/number type TRV’s on each radiator.  Am I correct in understanding you to say they are not required and, apart from bedrooms, should be turned right up to max, i.e. fully open and allow the main thermostat sole control? 

Posted by: @derek-m

Hi Batalto,

Having just watched the video accessed by the link you posted, I can now see why people's ASHP systems are not working at their optimum settings, if this is how they are being commissioned.

Hi @derek-m and @Batalto,

Can you repost the link please?  I can’t find it.

Hi Morgan,

Just find the statement from Batalto at the end of which is the word 'Link'. If you then click on Link it will take you to the youtube video.

@morgan

Hi Morgan,

I hope that you have now found the video.

Perhaps I should specify why I made the comment about the video in the first place. My comment was to do with the fact that they were recommending a minimum water flow temperature, from the ASHP, of 37C when weather compensation is active. As Heacol has pointed out previously, the lower the water temperature, the more efficient the system will be. By limiting the lowest water temperature at 37C, would mean that even during Winter, the ASHP could be switching on and off, rather than running continuously at a lower temperature, which is more efficient.