Changing the TRV

[shaneg]

Hi,

Bit new to plumping here so bear with me!

My rad in the kitchen is cold near the boiler and I think it's my TRV which needs replacing, now it's a MYSON 2 way valve, but i noticed it just screws off, but i'm terrified of taking it off all the way incase you get one of those moments you see on tv where water starts pouring out, will i have to isolate the radiator or is it a simple take it off buy the washing nut and put a new one on an not need to do anything else?

There is only the isolating valve at the other side of the rad which i turn with pliers do i turn this to isolate it as it hasn't a special screw value on the copper pipe?

Thanks in advance for the comments

Regards

Shane

 

[JohnD]

A TRV has two major sub-assemblies.

There is the valve part, which fastens to the radiator on one side, and the water pipe at the other, and has a valve which controls the flow of water, It has a pin sticking out of the top of it, which permits water flow when it is pushed down, and prevents water flow when it is allowed to spring up. The spring is not visible when the thermostatic head is in place.

There is the thermostatic part, which will have a graduated temperature control knob, and a part which pushes downwards (against the pin) when it is cool, and rises when it is warm.

These two parts are held together by a nut or clip. the thermostatic part can be removed from the valve. No water squirts out when you remove it.

If the valve appears to be permanently shut, the pin is probably stuck in the "down" position. Do not try to pull it out or you will break it. Try pushing it down and letting it spring up and perhaps it will come loose with jiggling. You will not be able to push it down with your thumb, but if you use a flat piece of metal you can do it. Only push it directly downwards, never sideways or diagonally, or it will probably break.

 

[D_Hailsham]

There is the valve part ... It has a pin sticking out of the top of it, which permits water flow when it is pushed down, and prevents water flow when it is allowed to spring up.

I have just looked at a TRV4; it's the other way round. Pin down = valve closed, pin up = valve open.

If you think about it, the wax/liquid/gas in the thermostatic head expands as it heats up and this makes the plunger push down on the pin to close the valve

 

[shaneg]

This is the TRv in question, the bit i can unscrew is the bit below the black section that i unscrewed a little, so is it safe to undo this silver locking nut to have a look inside at the pin?

If I need to replace the pin I'll need a whole new TRV in both parts, then i'll have to turn the water off correct???

http://www.bhl.co.uk/category/Myson_TRV_2_Way

 

[shaneg]

try this link sorry

****
I have edited it for you

Mod Rupert
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[shaneg]

Maybe this one?
http://www.heatingcontrolsonline.co.uk/myson-trv-way-trv-p-362.html

 

[JohnD]

it's the other way round. Pin down = valve closed, pin up = valve open.

quite right the pins get stuck down, and you need to wiggle them to make them spring out

 

[D_Hailsham]

try this link sorry

Set the stat to max and thent undo the large knurled nut underneath the white top, which will then come off. NO water will come out as you have not disturbed the valve.

You will see the pin sticking out of the top of the valve. It should go down when pressed and spring back when released. If stuck up gentle prressure should free it; if down, a tap with a hammer on the side of the valve should release it.

 

[shaneg]

Thanks people i'll have a peak at it