Grundfoss pump to powerful ?

[Graham J W]

Hi, I have recently had my central heating system replaced. The issue I have is with TRVs (Drayton TRV4s) noise and control. From what I have read it looks like water velocity ?. The TRVs / rads seem to be receiving very hot water very quickly. Consequently the TRVs make a hissing noise then close off before the rooms reach temperature. They come back on again and the cycle begins ?. The pump is a Grundfoss UPS3 and is set on speed 1. I have read that setting PP2 is an option. Apparently it is advised not to use this setting with a automatic by pass valve (I do outside the boiler). Valaint ecotech plus 424.

Any thoughts chaps.

 

[oldbuffer]

1. The TRVs react to room temperature, not water temperature, so they won't close down before the desired temperature is reached, at least in the air surrounding the valve.
2. The TRVs are silent. Any hissing sound is more likely to be air mixed with the water.
3. Turn the system off, wait ten minutes, then bleed all radiators, starting with the lowest and finishing with the highest.
4. Pump speed 1 is quite low. If the bleeding doesn't resolve the issue, try it on 2, but keep an eye on the Feed & Expansion (F&E) tank (if you have one) to make sure it is not pumping over into the F&E. If this makes an improvement, try again on 3, with the same proviso.

 

[Graham J W]

I am wondering if radiant heat from the rads is causing the TRVs to react early ?. The issues are more where the TRVs are controlling vertical column steel radiators. The system has been bled several times and the pump is quiet. No F & E tank as the system is sealed / pressurised.
Could it be a balancing issue ?. The system is split with valves / thermostats for downstairs, upstairs and HW.

 

[oilhead]

Turn the boiler stat down to reduce the very hot water coming into the rads. Check the flow and return temps of the rads to ensure they are balanced for temperature drop across the reads.

 

[Graham J W]

Boiler flow temperature set at 67 C. Return 55 C. I think I will have a go at balancing the system via the TRVs (Drayton TRV4s) using the Drayton balancing key. I have ordered some clip on thermostats to check across each rad as well.