Danfoss RAS-C2 TRV's radiator value adjustment

[PJ-DIY]

We moved into our current home 2 years ago, gas central heating was installed for us around that time.

Some of the radiators seem to have to drop to a low temperature for the thermostat to open the value. It then seems to heat up considerably before shutting off.

Can the valves be adjusted so that they open and close without such extremes?

 

[muggles]

Nope, they are what they are. New sensor heads might help

 

[PJ-DIY]

Oh dear, are they a problematic value?

Could a boiler contribute to the problem? Can a boiler be adjusted to narrow the cutting in and cutting out?

 

[oldbuffer]

The thermostatic radiator valves monitor the temperature of the air, not the temperature of the radiator. It is therefore important that the valve is reasonably well exposed to the general room air temperature, not hidden in a corner with little airflow, nor inside a radiator casing.

Its unlikely that the boiler is contributing to the problem. You could try turning the central heating water temperature down, which will give you slower heat up times but might reduce the "on / off" effect.

 

[D_Hailsham]

Some of the radiators seem to have to drop to a low temperature for the thermostat to open the value. It then seems to heat up considerably before shutting off.

That is normally a symptom of a badly balanced system.

1. Does the radiator in the room where the wall thermostat is located have a TRV fitted? If so, set it (TRV) to Max.
2. What temperature is the boiler set to for heating? About 70C is normally OK.
3. Remove TRV head and check the pin can be pressed down and pops up when released.
4. Check how far open the lockshield valve is on each rad. (That's the one at the opposite end to the TRV.) The plastic cap will normally pull off; then use a small spanner to turn the spindle - clockwise to close - count turns until closed then open up same amount.
5. If most of them are more than one turn open, the system has not been properly balanced.

How to balance a CH system provides full instructions, but a quick balance can often be achieved by setting all lockshield valves to half a turn open then tweaking each one (no more than 1/12th turn at a time) until the drop across all rads feel the same.

 

[PJ-DIY]

The boiler is a Worcester MT10
All radiators have TRV valves
When I checked today, the water pressure was approx 1.1 bar, I have now raised this to 1.5 bar.
The boiler temperature was set to just over number 4 according to manual this would be a temperature of just over 60 deg C, I have altered the dial to number 6 to raise it to 70 deg C.
Most radiators are on outside walls, under windows, and are not boxed in with furniture etc in front of them or in corners of rooms.

Over the next couple of days or so, we will test the heating at each radiator as the changes made today may require us to adjust some of the valves.

The room stat is in the hallway and is set at almost 20 deg C.
If the hallway temperature reached the room stat temperature would that knock 'everything' off?

Thank you for your help so far, we are very grateful.

 

[PJ-DIY]

Reading my above post I need to clarify one item.
All radiators have TRV valves, the towel rail radiator in the bathroom doesn't.

 

[D_Hailsham]

MT 10 is the model no of the programmer. The boiler model no will be on the Installation Manual which the installer should have left you; it will be a Greenstar XXX.

Set TRV to max for rad controlled by room stat

You shouldn't need to adjust the TRVs as they control room temperature, i.e a setting of 4 will give a temperature of about 20C. if the radiator is not giving off sufficient heat - too small or water temperature too low - setting the TRV to a higher setting will not help.

Yes, the room stat will knock everything off when it reaches the set temperature. It may be possible to affect this by reducing the output of the radiator controlled by the room stat - close the Lockshield valve to do this - so the room heats up slower.

 

[PJ-DIY]

I have today raised the room stat in the hallway from 19.5 C to 25 C, the TRV on the hall radiator is set lower than the rest of the bungalow, so that the hall doesn't get as warm and the room stat doesn't switch off the system and affect the other room radiators.

I can now start to monitor the temperature in each room, this may take a couple of days and nights and adjustment may be needed.

I will confirm the findings, thank you for your help.

 

[D_Hailsham]

I have today raised the room stat in the hallway from 19.5 C to 25 C, the TRV on the hall radiator is set lower than the rest of the bungalow, so that the hall doesn't get as warm and the room stat doesn't switch off the system and affect the other room radiators.

That's OK as a temporary measure while you monitor the other rooms, but it will mean the boiler continues to run long after the TRVs in other rooms have operated.

If you find that a room does not get up to temperature it will be because either the radiator is too small or the mean water temperature is too low.

Please post the results back to this topic.

Have you checked if the system has been balanced?

 

[PJ-DIY]

Hi

What do you mean when you say... Have you checked if the system has been balanced?

 

[PJ-DIY]

I have today raised the room stat in the hallway from 19.5 C to 25 C, the TRV on the hall radiator is set lower than the rest of the bungalow, so that the hall doesn't get as warm and the room stat doesn't switch off the system and affect the other room radiators.

That's OK as a temporary measure while you monitor the other rooms, but it will mean the boiler continues to run long after the TRVs in other rooms have operated.

If you find that a room does not get up to temperature it will be because either the radiator is too small or the mean water temperature is too low.

Please post the results back to this topic.

Have you checked if the system has been balanced?

Hi, when you say OK as a temporary measure, surely the hall radiator will always need to be less than the room stat or the increase in heat from that radiator will cut off the system via the room stat?

 

[D_Hailsham]

Hi

What do you mean when you say... Have you checked if the system has been balanced?

See items 4 and 5 of my earlier post:

//www.diynot.com/diy/threads/drayton-trv4-radiator-value-adjustment.442641/#post-3467056

 

[AlanE]

Hi, when you say OK as a temporary measure, surely the hall radiator will always need to be less than the room stat or the increase in heat from that radiator will cut off the system via the room stat?

You are better off removing the head from the hall radiator and then making sure the radiators are reasonably well balanced.

The thermostat in the hall should be set to bring the hall to correct temperature. The rest of the rooms should then follow and reach their designed temperature, unless of course outside influences like opening an outside door throws the whole system out of sync.

Back in my working days repairing heating systems I always suggested the wall thermostat should be installed in the room that the house occupants considered most important to maintaining creature comfort - the living room.

It is important that whatever room has the thermostat there are NO radiator valves on that rooms radiators otherwise they 'fight' each other!

Consider the scenario - room warms up and radiator valve switches off, so effectively cooling the room. Wall thermostat merrily does its thing and carries on heating the rest of the house as room it is installed in is no longer being heated.

The heating system is designed, and balanced so that when the 'controlled' room reaches desired temperature the rest of the house has also. Only real exception is the hallway when the front door is opened. In this case, if thermostat is located in the hall then cold draft causes thermostat to call for heat with the effect of overheating rest of the house.

 

[D_Hailsham]

Only real exception is the hallway when the front door is opened. In this case, if thermostat is located in the hall then cold draft causes thermostat to call for heat with the effect of overheating rest of the house.

I agree with everything else you wrote - saved me writing it! However you seem to have forgotten that TRVs are controlling the temperature in other rooms so they will not overheat when a cold draught switches the wall stat on.

I do wonder if the "cold draught" problem is more associated with the old mechanical stats as I have never noticed my CM927 call for heat when the front door is open - and it's situated immediately opposite the door.