TRV won't allow flow, flow OK without TRV head.

[Justin C]

I'd like to avoid calling the plumbers back if I can.

Last week we had two stuck-shut TRVs replaced, the new ones are marked Bulldog gen2. We were looking forward to being warm again but alas, twas not to be. I thought that maybe the rad needed flushing, so did that myself yesterday - it did need doing but didn't fix the issue.

I took the head off the TRV and the radiator was too hot to touch within a few minutes - result! But then the TRV cut flow before the room got up to a habitable temperature. I compared the head with the other one they fitted and the plunger was much more proud, I swapped them over (the other is in a room infrequently used and we don't mind it being chilly). That'll do it I thought, except no... within a short time the heat from the rad had expanded the (whatever it that makes these work) and we were in the same situation.

So, even at 'full-open' these TRVs cut flow before the room is warm, we're constantly chilly. Can these be adjusted somehow (I can't see it if they can - short of taking a dremel to the plunger in the head). Or do I need to call the plumbers back in?

If I barely put the head on - so the fixing ring threads only just grip - 1/8 to 1/4 turn - we have the kind of temperature we want, but that's not right.

Suggestions gratefully received.

Justin.

[Roger Mills]

It sounds as if these are the wrong heads for the TRVs. Were the whole things replaced, or only the heads?

[DerbyBorn]

.

I agree with the previous suggestion - another is that the adjusting head may have been removed and refitted on the wrong "start" of the multi start screw thread. Usually a stop prevents this - but if the stop is removed then it is possible to take the cap off. I did this once and had a devil of a jog getting it to respond properly to "3" on the dial.

[harry]

That is the problem with TRVs. They are influenced by the radiator/nearby pipework as much/more than the room temperature. It's why some are installed horizontally. (To get the head further away from the radiator) Or sometimes even in outlet (cooler part) of the radiator/pipes)

[Justin C]

That sounds logical. I don't know if the TRV was replaced, or only the head.

Yesterday we were fed up with being chilly so I took the head off the TRV and before long we were too warm!

It sounds like I need the plumbers to come back.

Justin.

[Roger Mills]

TRVs do have their limitations - but there's something definitely wrong in the OP's case. I suspect that the heads are the wrong ones for the valves.

[RobertL]

You can get TRVs with a small 'linking pipe'. You mount the sensor-head on the wall slightly remote from the radiator.

Robert

[Chris Hogg]

Assuming there is one, you could turn down the lock-shield valve* to restrict the flow through the radiator a bit more and stop it getting so hot.

*If you don't know it, that's the valve at the other end of the radiator, opposite the TRV, that's got a plastic dome cap and a square-ended shaft. Use a spanner or pipe wrench to turn it.

[Alan Dawes]

Possibly a stuck or sticking pin see:

for possible solutions (that person had one sticking open) - Including WD40 and gently wiggling the pin.

Alan

[Justin C]

I mentioned your suggestion to my wife, she says she is sure they are new TRV because one was seized, and rust coloured, the replacements are shiny and new looking.

Justin.

[Justin C]

Nothing wrong with the pin, I take the head off the TRV and it's like an oven in here.

Justin.

[DerbyBorn]

Has the knob been removed and then screwed down too far before the stop was fitted? (which limits it to one turn)

[Justin C]

While the head removes easily, it does not appear to come apart in a non-destructive way, I have looked very closly.

As I mentioned in my first post, if I only just engage the threads of the head onto the body of the valve it works OK, but as I start "doing up" the nut (knurled ring) the head is pulled down and flow reduced. Then, as everything gets warm (TRV head in proximity of rad) flow is shut off but before the room is warm enough.

While I could leave the head only partly engaged with the threads, I I don't like that idea, all it would take is someone who doesn't know to give it a tweak and they've got a TRV in their hands!

Justin.

[DerbyBorn]

Justin C wrote in news: [e-mail]:

Mine have removable limit stops - which if removed allow the knob to make an extra turn.