WElcome to the forum.  My first post was eaten by some gremlin, so I am trying to reproduce it here.

Firstly, we need some information about the system itself, does it fo hot water as well as the heating?  What sort of controller do you have for it, maybe a brand name and type or a photograph of it?  Did the builder leave you any proper instructions about how to operate it, or even a manual? 

Are all the thermostats set to the same temperature? 

@guthrie 

It does do hot water as well but we’ve currently switched it off as we felt it wasn’t coping doing water and heating. So the immersion is doing the hot water for now. 

The controller is just the standard Grants controller. We don’t have a hub or anything.

We’ve been left with no manual. But i did have it at one point and it was useless. I think it was more for the installer than us.

 The builder is clueless too! Which is why I’m becoming desperate.

Downstairs the thermostats are set to 20 degrees. Upstairs are set between 16.5 and 17.5 because I’ve got to the point where I know it’s not going to reach higher temperatures and I’m trying not to let it get any colder!

I really need help. 

Posted by: @dreamkeela

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@guthrie 

It does do hot water as well but we’ve currently switched it off as we felt it wasn’t coping doing water and heating. So the immersion is doing the hot water for now. 

The controller is just the standard Grants controller. We don’t have a hub or anything.

 

We’ve been left with no manual. But i did have it at one point and it was useless. I think it was more for the installer than us.

 

 The builder is clueless too! Which is why I’m becoming desperate.

Downstairs the thermostats are set to 20 degrees. Upstairs are set between 16.5 and 17.5 because I’ve got to the point where I know it’s not going to reach higher temperatures and I’m trying not to let it get any colder!

I really need help. 

Please post some photo's of the equipment within your system, so that the forum can get some idea of how your system has been installed.

Hello and welcome. The Grant Aerona units are known to spend a lot of time in defrost in winter conditions, usually every 45-60 minutes. That does seem more than other brands - weather such as the damp and relatively mild winter weather we've recently experienced. This reduces the unit heat output and it can struggle to reach target heating flow temperature. That in turn means insufficient heating into the UFH system. It also means the electricity consumption rockets too, as the unit is working more or less flat out between defrosts - it never gets chance to modulate down to a low speed control.

It might seem perverse, but it could be the 6kW unit is undersized for a 3bed new build. The heat loss calculation done by the developer or builder might be less than 6kW, but in the weather we've recently had, the Grant Aerona unit might not be outputting 6kW, probably somewhere between 4-5kW based on several members here with varying capacity Grant units who have all seen flow temperatures drop several degC below target set point, me included. Grant has a product called a 'volumiser/low less header' which has a 3kW immersion heater that can be used as supplementary or emergency heating. It's an expensive power consuming option however. It does rather hint that they realise there are times their Aerona branded ASHP products don't provide enough heat output

The Grant unit controller is complicated, most Grant installs use a simpler external digital programmable thermostat and water time clock + cylinder thermostat. The Grant controller is able to do all that, and much more besides, but it has to be said programming it and adjusting parameters on it isn't easy or intuitive. Fear not, plenty of people here can help.

Grant has a history of commissioning systems with weather compensation disabled, (WC is an automatic modulating control where the heating flow temperature increases as the outdoor air temperature decreases and vice versa), and their installs have too much reliance on on/off room thermostat controls instead. That's not good for ASHP efficiency.

The grant unit can only supply water at one temperature, so having downstairs and upstairs zones with different thermostat settings may complicate things. Your UFH might have some thermostatic blending or flow control for each zone, but this often isn't the most efficient heating method with ASHP. As @Derek-m and @Guthrie have mentioned, put some details up on here and you'll certainly get some help and advice.

Quite a few Grant Aerona owners have found their units struggling this last week or so, (me included), but the weather has been somewhat exceptionally cold. 

Hopefully things have improved now the cold snap has reached its end ... ?

There are many (too many) parameters to consider to improve performance, but it might also be worth checking some obvious things first. For example, check the airflow around the outside unit (I found at the weekend a gutter was dripping water onto it; the heat pump air caused that to freeze so there was a frozen waterfall blocking part of the fan flow) to ensure nothing's in the way; try to identify if you have an auto bypass valve near to the low loss header, and if so, make sure it's practically closed; if you have a secondary pump try a day on a different speed to see if it's better or worse.

Sorry that you are having difficulties. Installers ought to know more about that they're doing, and do a proper handover.