TRV functionality when weather changes.

[gerardo]

Hi,

We have a Remeha system boiler in the kitchen extension, with a Honeywell CM927 managing the temp with the the sensor in the extension as that's the coldest room. That works well, no problems.
However, some of the rads were changed and also had TRV's fitted (Pegler Bulldogs). It seems that these TRV's do not manage to provide a stable temp; they seem to function more like a standard valve which is adjusted to give more or less flow. They will, if turned to extremes, shut off or stay on, but when a setting equilises, there is allways a flow when the boiler is on.
The result is that, as the outside temp rises, the room is getting too warm.
I thought that a TRV should, given enough hot water, maintain a stable temp and not go too warm.
I would like to ask some advice as to whether I should look at replacing these TRV's as I have a Honeywell and a Regis (TRV) in other rooms that seem to be more consistent at maintaining a stable temp.........or am I doing something wrong?

 

[PRS1]

It maintains the temp u set it to but if u have doors between rooms open this will interfere with this, also trvs are usually 8" off the deck so if there is any draughts etc these will affect them also.
Just persist with them and try to find a level which you are comfortable with then leave them as they are.

 

[D_Hailsham]

some of the rads were changed and also had TRV's fitted (Pegler Bulldogs). It seems that these TRV's do not manage to provide a stable temp; they seem to function more like a standard valve which is adjusted to give more or less flow. They will, if turned to extremes, shut off or stay on, but when a setting equalises, there is always a flow when the boiler is on.

Was the system rebalanced after the new rads and TRVs were fitted? If it wasn't, that is the likely cause; if it was, then the job wasn't done properly!

Read How to balance a CH system

A TRV will be full open when the room is cold, but as it approaches the set temperature it will start to close down until the flow is sufficient to maintain the required temperature. It is not a switch.

 

[bengasman]

...We have a Remeha system boiler in the kitchen extension, with a Honeywell CM927 managing the temp with the the sensor in the extension as that's the coldest room.

That's not a good way of doing things, see faq

That works well

Clearly not; you wouldn't be here if it did.

However, some of the rads were changed and also had TRV's fitted
The result is that, as the outside temp rises, the room is getting too warm.

Then your setting is too high

 

[gerardo]

...We have a Remeha system boiler in the kitchen extension, with a Honeywell CM927 managing the temp with the the sensor in the extension as that's the coldest room.

That's not a good way of doing things, see faq

Not sure why, it keeps the extension at a consistent temp as the wired remote wiring is in the hall.

That works well

Clearly not; you wouldn't be here if it did.

The CM927 and boiler work well; the issue is with the lounge temp varying as the extrernal temp has risen recently, hence the question.

However, some of the rads were changed and also had TRV's fitted
The result is that, as the outside temp rises, the room is getting too warm.

Then your setting is too high

I thought TRV's regulated the temp, so once set, they would adjust the flow to suit and not overheat the room when the external temp rises.
I can understand a rad not getting enough heat, hence the room does not heat properly.

 

[D_Hailsham]

I thought TRV's regulated the temp, so once set, they would adjust the flow to suit and not overheat the room when the external temp rises.

That's quite correct - see my earlier answer. But the flow rate though the rad, when the TRV is fully open, must be correct and so must the pressure difference across the TRV. Both of these are set when the system is balanced.

If the TRV is staying open all the time it means that the flow rate and pressure is higher than the TRV can handle - a bit like trying to walk into a force 10 headwind.

 

[bengasman]

I thought TRV's regulated the temp, so once set, they would adjust the flow to suit and not overheat the room when the external temp rises.
I can understand a rad not getting enough heat, hence the room does not heat properly.

See faq