Daikin Altherma - radiator balancing

[Steve W]

I have recently had a Daikin Altherma 7.5Kw heat pump installed in place of a bosch gas boiler. The downstairs is UFH with 8 zones and auto balancing flow controllers. The upstairs is radiators with individually controlled radiator valves (TADO). There is an ESBE valve which controls whether the tank gets the hot water or the two heating circuits (2 x 2 port valves). The UFH and DHW work as expected and I've been getting a COP of 3.5 (heating / DHW).

 

As the weather has been mild the upstairs of the house has required little or no heat and hence not paid any real attention to it.

 

Tonight was quite cold so I turned on a couple of radiators. Which got to a reasonable temperature - enough to warm the room. After about 10 minutes the flow and return temperature converged and the flow rate dropped.

The flow rate dropped to zero and essentially there was no more heating.

 

I will be ringing the installer tomorrow but would like to have an understanding why this has happened. Looking back this is probably not an isolated occurrence.

 

I should add that the reason for individual controls is that it is extremely easy to overheat the rooms given the level of insulation.

[Marvin]

Do you have abuffer tank?

 

Is the esbe valve system set to prioritise the hot watertank?

 

 

[Steve W]

There is a 10 litre buffer tank in the return leg from the heating circuits. So when heating the DHW the return water doesn't go through the buffer tank. There is an ESBE valve which takes priority - the DHW is heated between 12.30am to 01.30am followed by the UFH and finally the radiators. There is no overlap between the functions.

[ReedRichards]

9 hours ago, Steve W said:

Tonight was quite cold so I turned on a couple of radiators. Which got to a reasonable temperature - enough to warm the room. After about 10 minutes the flow and return temperature converged and the flow rate dropped.

The flow rate dropped to zero and essentially there was no more heating.

 

Isn't what you describe the intended function of a radiator valve once it reaches the set temperature?  In my experience automated radiator valves are too close to the water pipes and the radiator to accurately determine the room temperature so you might need to compensate for this by setting the requested temperature to something a bit different to what you actually want.  

[Steve W]

It wasn't getting anywhere near the radiator set point temperature before the flow from the ASHP drops ro zero. With all the radiators on this morning the problem doesn't appear to occur in that all radiators got hot water and the rooms heated to the correct temperatures. I have also adjusted the lockshield valves on a couple of the radiators at the end of the pipe run.

[Steve W]

Balancing the radiators seems to have fixed the problem and all rooms are achieving the correct temperature.