Replacing TRV

[Johnking]

Hi,

A very old Drayton TRV3 has failed closed, I need to replace it. I don't fancy the pipe freeze method, so as I understand it I need to drain the system. I have read the wiki but still have some uncertainty

1. Do I need to drain the whole system? It's a combI with filling loop.

2. Do I need to open the bleed valve on all the rads to fully drain the system

3. When refilling, I think I have to close bleed valves, refill to 1.5bar, then start bleeding and repressurizing. Do I start this process with the lowest rad and work up the house - 3 floors?

4. Will I need to do any pipe work? I will the new TRV, which will not be a Drayton TRV3, fit, or are they all different dimensions?

5. Does one use plumbers mate, or ptfe tape, on the TRV joints?

6. The top most rad is a towel radiator with vertical bleed valve - is that where I can pour inhibitor in, prior to refilling?

Sorry for all the naive questions, I'm not completely new to plumbing but it would be a bad time of year to knacker the heating!

 

[oldbuffer]

1. If you are new to this, drain the system. You only need to drain down to just below the level of the valve you are changing.
2. No, only the ones above or at the same level as the radiator you are working on.
3. Yes.
4. You should be OK, unless the TRV3 has "union" fittings, rather than compression fittings. Picture would enable us to confirm.
5. If you are reusing the old nuts and olives, 3 or 4 wraps of PTFE around the old olives can help them seal better. No plumber's mait. Could use Jetlube V2. If using all new, shouldn't need anything.
6. Provided the bleed valve is set into a removable (often chrome plated) nut, then remove the nut and pour in the inhibitor. If you are new to it, consider refilling and bleeding, use the system to make sure you have no leaks, turn off, remove plug from towel radiator, syphon out 1.5 litres of water, add inhibitor, final bleed.

 

[Johnking]

Thanks for taking the time to reply. Couple more clarifications before I head off to Screwix:

1. If you are new to this, drain the system. You only need to drain down to just below the level of the valve you are changing.

How do I control the level I drain to?

4. You should be OK, unless the TRV3 has "union" fittings, rather than compression fittings. Picture would enable us to confirm.

I think they are compression - see attached pic. So would this one directly fit in : https://www.screwfix.com/p/drayton-rt313-white-angled-trv-15mm-x-15mm/3715r

6. Provided the bleed valve is set into a removable (often chrome plated) nut, then remove the nut and pour in the inhibitor. If you are new to it, consider refilling and bleeding, use the system to make sure you have no leaks, turn off, remove plug from towel radiator, syphon out 1.5 litres of water, add inhibitor, final bleed.

This sounds wise - but how to depressurize the system to allow me to syphon out? Better just to drain out 1.5l from downstairs while towel rad bleed valve is open?

Thanks oldbuffer!

 

[terryplumb]

If the existing valve is permanently closed , is it just the pin stuck ? Could save yourself a lot of work if you just free / lubricate the pin ??

 

[Johnking]

If the existing valve is permanently closed , is it just the pin stuck ? Could save yourself a lot of work if you just free / lubricate the pin ??

Pin was indeed stuck. Wiggled, pushed, pulled, accidentally removed it. Pushed it back in a hurry, tiny amount of water. It has no springiness and won't push any further.

 

[Elkato531]

Someone who knows what they're doing could have that valve changed in 10 mins without draining the system. (providing the furniture is moved out of the way). A minimum charge will probably be payable but you won't need the inhibitor. May be worth it.

 

[terryplumb]

OK ,replacement job then . as posted above by Oldb.

 

[oldbuffer]

You're clearly not the only one with this problem!

Look at http://www.directheatingsupplies.co.uk/drayton-trv4-to-trv3-conversion-sensor-head-07-94-012 - no water involved!

If still replacing, then:

1. Drain some water out from radiators above. Slacken nut connecting pipe to radiator. If water comes out (more than a dribble) re-tighten, drain more from above, repeat.

2. I can't tell for sure from your picture whether its a union or compression. If nut at side of valve next to radiator and nut at bottom of valve by incoming pipe are the same size, then probably compression. If not, probably union. You can get TRVs with union connections, but they're very expensive. You could use a compression one by changing the tail which goes into the radiator (normally comes with the valve). However, it looks like a very cramped space to try and take the old tail out. You'd also need a tail removal tool (e.g. Toolfix 11467), they're not very expensive.

 

[Johnking]

Thanks, so trial and error for draining it is. Those converter heads are the wrong bit for me, it's the valve body i need. I think I have compression joints.