TRVs - A Theory and a Question

[ijc]

Hi

Living in an old and energy inefficient house, I've noticed something of a problem with TRVs. Just wondered if anyone would like to comment on the semi-baked theory I've got to explain it.

On very cold winter days the heating belts out for hours and the room warms up. Lovely. However, if the radiators are on for long enough the TRVs close and stay closed even when the room gets cold again. I think this is because a bit of a "heat island" is formed around the TRVs by the (very hot) input pipe and the valve itself getting hot. You can feel the warmth around the valve when the rest of the room is chilly.

Questions are...

Is this a known phenomenon?

Can the valves be re-calibrated somehow?

Can I buy TRVs which will simply stay open when set to the highest setting?

At the moment I'm wrapping dusters around the things to keep the heat away from the sensor on cold days!! (v silly)

Thanks for your wisdom!

Ian

 

[kevplumb]

if they are 1/2"" in and out

you could simply turn the valve so the head is horizontal

i seem to recall danfoss recomending this at one time

 

[ijc]

if they are 1/2"" in and out

you could simply turn the valve so the head is horizontal

i seem to recall danfoss recomending this at one time

Cheers, that never occurred to me but makes total sense.

Much appreciated!

Ian

 

[Elkato531]

A hot object in a cold room will cause air circulation by convection. As heat rises, cooler air is drawn in from underneath. This should ensure that the TRVs work. Wrapping dusters round them or restricting air flow with furniture will prevent them working correctly.

 

[Elkato531]

Another thought

If you have a room stat in your living room this will be providing an interlock and shutting the heating down once the room is up to temperature. Once this happens, it doesn't matter what Your TRVs are set at in other rooms. The heating will not come back on until the temp in the living room drops by which time the rest of the house can be chilly.

You need to check if the boiler is firing and the pump running when you think the TRVs are failing to open.

 

[Goldberg]

I think this is because a bit of a "heat island" is formed around the TRVs by the (very hot) input pipe and the valve itself getting hot. You can feel the warmth around the valve when the rest of the room is chilly.

If the radiator is emitting heat then it will eventually cool down, and so will the valve, since no water is flowing.

If the valve is staying shut when it shouldn't then either the head is faulty is the valve is sticking shut.

Elkato531's point is also a good one.

 

[kevplumb]

this is of course based on your extensive experience within the plumbing and heating industry

what's your occupation again

 

[ijc]

I think this is because a bit of a "heat island" is formed around the TRVs by the (very hot) input pipe and the valve itself getting hot. You can feel the warmth around the valve when the rest of the room is chilly.

If the radiator is emitting heat then it will eventually cool down, and so will the valve, since no water is flowing.

If the valve is staying shut when it shouldn't then either the head is faulty is the valve is sticking shut.

Elkato531's point is also a good one.

This is the key to it - the radiator is going cold but the in-pipe which is underneath the valve is staying very hot. I think this is keeping the valve warm and thus closing the thing up. Cold room / cold radiator / warm valve / unhappy household!

The system doesn't have a room thermostat - just TRVS - and the boiler and pump are fine. So I think Kev's suggestion is sound. If the valve is attached so it's sideways on, then warm air rising from the in-pipe will hopefully not affect the valve as much because the valve won't be directly above.

This is what the dusters were there for - insulating the in-pipe so it can't warm the valve above. That did seem to help.

Thanks again to all - much appreciated.

Ian

 

[Goldberg]

This is the key to it - the radiator is going cold but the in-pipe which is underneath the valve is staying very hot.

Well, if the pipe is VERY hot then there's hot water flowing through it, which means that the valve is partly open.

There is that alternative explanation:

The system doesn't have a room thermostat - just TRVS - and the boiler and pump are fine. So I think Kev's suggestion is sound. If the valve is attached so it's sideways on, then warm air rising from the in-pipe will hopefully not affect the valve as much because the valve won't be directly above.

This is a possibility - the valve is closed, but the distribution pipework is sufficiently hot and nearby for heat to reach the valve by conduction through the pipe or convection through the air. Do you have bare floorboards with a large gap around the pipe where it goes through?

My feeling is that that the valve is sticking fully or nearly shut. Since this is commonplace, it's worth spending some time to see if yours is sticking.

There are plenty of topics covering this, but the basics are that you remove the thermostatic head and test the movement of the pin to see if it travels freely. If you wait until the problems occurs, and then remove it, then you may discover that the pin is stuck down.

If it is, then replace it with a decent one, and since you'll be draining down to do it, assess the condition of the system water - many TRVs stick because of deposits resulting from corroding radiators, and the fact that your house is old makes me wonder whether or not the heating primary circuit is chemically protected against corrosion.

 

[kevplumb]

This is the key to it - the radiator is going cold but the in-pipe which is underneath the valve is staying very hot.

Well, if the pipe is VERY hot then there's hot water flowing through it, which means that the valve is partly open.

There is that alternative explanation:

The system doesn't have a room thermostat - just TRVS - and the boiler and pump are fine. So I think Kev's suggestion is sound. If the valve is attached so it's sideways on, then warm air rising from the in-pipe will hopefully not affect the valve as much because the valve won't be directly above.

This is a possibility - the valve is closed, but the distribution pipework is sufficiently hot and nearby for heat to reach the valve by conduction through the pipe or convection through the air. Do you have bare floorboards with a large gap around the pipe where it goes through?

My feeling is that that the valve is sticking fully or nearly shut. Since this is commonplace, it's worth spending some time to see if yours is sticking.

There are plenty of topics covering this, but the basics are that you remove the thermostatic head and test the movement of the pin to see if it travels freely. If you wait until the problems occurs, and then remove it, then you may discover that the pin is stuck down.

If it is, then replace it with a decent one, and since you'll be draining down to do it, assess the condition of the system water - many TRVs stick because of deposits resulting from corroding radiators, and the fact that your house is old makes me wonder whether or not the heating primary circuit is chemically protected against corrosion.

christ did you get all that off google or just searching old posts

 

[davebgas]

No kev, asked someone on Yahoo answers

 

[BingoBongo]

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Untitled

• BingoBongo
• 1 Nov 2009
• 2

 

[davebgas]

love it

 

[ijc]

This is the key to it - the radiator is going cold but the in-pipe which is underneath the valve is staying very hot.

Well, if the pipe is VERY hot then there's hot water flowing through it, which means that the valve is partly open.

There is that alternative explanation:

The system doesn't have a room thermostat - just TRVS - and the boiler and pump are fine. So I think Kev's suggestion is sound. If the valve is attached so it's sideways on, then warm air rising from the in-pipe will hopefully not affect the valve as much because the valve won't be directly above.

This is a possibility - the valve is closed, but the distribution pipework is sufficiently hot and nearby for heat to reach the valve by conduction through the pipe or convection through the air. Do you have bare floorboards with a large gap around the pipe where it goes through?

Well there's 6 inches of bare pipe below the valve (no real gap in the floor), and as long as that pipe's filled with hot water it will send up warm air by convection and the valve fitting itself will get hot by conduction.

Can't do anything about the conduction, but convection is lessened if the valve is to the side of the pipe.

Of course the problem would be solved if I could find TRV with a fully open setting as well as a fully closed one.

 

[JayJay1978]

BingoBongo, its not like you to use that kind of langauge, on a Sunday as well.