@trebor12345 As you can see the community is discussing ideas on how you might best control this system. I have been reading the user manual. You have, so far as I can see, a brilliant piece of kit with a vast range of capabilities. Of course that makes it complex so we need to simplify it.
Your challenge is the house. It has, in essence, a 100kWh storage heater sitting underneath it, and the only control you have over that is the amount of energy you put in (actual storage heaters have flaps and a fan so you have some control over the energy you get out). As a result of this and your high level of insulation your house retains heat extremely well, it loses less than 2C in 24hrs even if its freezing outside. This also means that it responds very slowly to any changes you make to settings, think timescales of a day not hours!
Together these mean that the main control, to have any chance of success, has to be 'forward looking'; control based principally on current room temperature is simply not going to cut it. I am pretty certain this is why you are having problems. You would have exactly the same problems with any other heating, its the nature of the house.
This means, I think, that we have to get weather compensation set up and get that doing the heavy lifting. We can help you with that.
Incidentally the unit will also do cooling and since you have UFH cooling is definitely possible. The buffer tank, which is anyway a pain and entirely pointless given the size of the buffer under the house, would have to go though to do this, which you may wish to defer.
If its difficult to collect past data you could forget about it and just 'make a fresh start' under guidance from those here. The data we absolutely do need however is:
What temperature do you want the heating to be at?
If its not set to operate 24*7 whatisit set to do or is that changed constantly also?
have you tried to set up weather compensation and failed/abandoned, or have you never set it up?
If you havent set up WC is it set to run at a constant flow temp and if so what is that (you have said 31 and 33 above, which or are you manually varying that?)
Where is the thermostat located relative to where you have measure the room temp. What make and model of thermostat or is it the internal one?
Where is the hitachi controller located and is is set to ignore its own temperature sensor?
What controls the secondary pump (ie the pump on the buffer side of the UFH)?
Is solar gain a factor in keeping temperatures under control and if so to what extent
Without this information its going to be difficult to guide you.
Obviously nothing is guaranteed, but Im pretty confident that (unless there is something wrong that has not yet emerged) this is a good piece of kit for your house. It is oversized, but any heat pump or boiler will be so I cant see that replacing it will help.
Please respond if you are ready to give it a go. Of course if you do have the past data that would assist even further, but if its difficult to collect together maybe just make a fresh start. If you do decide to give it a go you will need a couple of weeks to tweak things and will need to check back here frequently.
Of course OPs is further complicated by that blessed, pointless, and wholly inadequate buffer and (presumably) a secondary control loop trying to do its own thing quasi independently of the heat pump. Somehow, if batch heating it the way forward (and I agree it is), that needs to be synchronised to the heat pump, otherwise we will likely end up with the heat pump switching on according to its batch schedule, but the buffer/secondary control loop refusing to forward the energy to the UFH! Its tempting to start with the secondary pump running 24x7 and then, once its refined (or the a decision taken that it wont work) try to finesse the secondary pump control. That of course is assuming the buffer isnt located in a unheated garage.
2024 build bungalow
Southern england 179 m2 High level of insulation Underfloor heating All 12 circuits are fully open all the time 1 thermostat in family room 7KW heat pump 50 litre buffer tank (4 port)
3.6KW solar panels Energy used by heating 2527 KWh - 7527 KWh (SCOP 3.5 approx)
