Change A TRV on Pressurised System

[50020]

How do I change a TRV on a pressurised system?​

A couple of weeks ago, I noticed the bathroom floor had 'dried water' underneath the towel rail / radiator. I checked the radiator for leaks, and it was bone dry all around it and the connecting pipes. I left it for a few days, keeping my eye on it, just in case it wasn't a sopping wet towel which had been left, and sure enough there was a signs of a drip. Placing a tub underneath, the following day it collected circa 10ml of water.

Taking off the TRV, I am greeted with the picture below - but it's hard to determine exactly where it was weeping, either around the 'pin' or elsewhere. Either way, the valve needs replacement [although since fannying around with it, it seems to have stopped weeping].

I have seen a couple of you tube videos, they change TRVs, but not on a normal boiler with a two circuit pressurised system. The suggestion is to relieve pressure from the radiator (two pipe system) using the bleed valve, and then close it. Then turn the other radiator valve off (are they called lockshields?) and that will help effectively air-lock the water in the system and radiator (like a finger on the top of a straw), so I can remove the TRV (obviously there will be limited leakage). I would hope to utilise the existing olive/nut etc. Is it that straightforward on a pressurised system? Or would I need to drain the system?

 

[Mottie]

I have seen a couple of you tube videos, they change TRVs, but not on a normal boiler with a two circuit pressurised system. The suggestion is to relieve pressure from the radiator (two pipe system) using the bleed valve, and then close it. Then turn the other radiator valve off (are they called lockshields?) and that will help effectively air-lock the water in the system and radiator (like a finger on the top of a straw), so I can remove the TRV (obviously there will be limited leakage). I would hope to utilise the existing olive/nut etc. Is it that straightforward on a pressurised system? Or would I need to drain the system?

Yep. Once you have let the pressure out, you have an effective vacuum. Very little will leak out. Just have the new parts ready, remove the old parts and job done. Obviously you’ll have to refill/pressurise when finished.

 

[Elkato531]

There needs to be some movement of the pipes in order to replace the valve. You may have to release the towel rail from its mounts and lift slightly. Make sure the new valve has the same dimensions as the old one so it goes back together easily.

 

[50020]

There needs to be some movement of the pipes in order to replace the valve. You may have to release the towel rail from its mounts and lift slightly. Make sure the new valve has the same dimensions as the old one so it goes back together easily.

Yes, I’ve measured it, and if I need to do the tail in to the bottom of the radiator, I can do if I have to, but I do want to avoid that if I can.

Thanks all ….

 

[50020]

How I Successfully Changed a TRV

Thanks for the comments above. I thought I'd share that following the above instructions and advice I managed to successfully change the TRV on the Bathroom Towel Rail.

My CH system, is a two circuit with hot water tank, radiators being fed by twin pipes.

I searched more on YouTube and came across this Video from the "The DIY Guy2, which was a bit of a help, and confidence boost (I don't like messing with water pipes!)

How to Change a Thermostatic Radiator Valve Without Draining The System

After watching that I armed myself with the following.

Good Home Polished Chrome-plated Straight TRV from B&Q
Boss White Pipe Jointing Compound from City Plumbing
Two Adjustable Spanners
Radiator Bleed Valve Key
Bucket
Towels
1M Length of Hosepipe

What I Did - Only replaced the actual TRV, keeping the Old Nuts and Olives on the existing Radiator and Pipe

1. Turn off central heating
2. Place plenty of towels around the area to soak up spillages, splashes etc.
3. Put some jointing compound on the treads of the TRV, making sure the decorators cap is on it, and thus closing the valve.
4. Open the bleed valve to release the pressure from the system. I used a length of hosepipe to direct the water from the bleed valve in to the bucket. I kept draining until pretty much all the water had stopped squirting out, there was still a constant dribble, but the video mentioned above and other videos suggested this would always be the case.
5. Close the lock-shield valve. I marked one side of the lock shield valve with a sharpie, and counted the number of turns required to completely turn it off. I counted just shy of 3 full 360degree turns, but made a mental not of the position of the valve. This ensures it is open at the same flow rate as before I started.
6. Empty the bucket from step 3.
7. Loosen the radiator holding brackets. The amount of movement above the existing TRV meant that even undoing the nut, would not be possible without lifting the radiator slightly.
8. Close the TRV. I am not sure this step is necessary, as the next step is against the clock, simply to complete it as quickly as possible.
9. I undid the nut on the radiator side first meaning at worst, only the water from the radiator would need to be accommodated. The water does drain in a glugging motion, but this is managed so long as the TRV is still in situ, while I
10. Undid the central heating pipe side.
11. Jiggle/Lift very carefully the radiator so the TRV can be extracted. Obviously it was important to be very careful here so as not to damage the lock-shield connection. Water will glug out of the radiator, but slowly at this point, and also water will rise up out of the CH pipe, again this isn't an undue amount as there is little to no pressure there. placing a thumb on top of the pipe would easily stem the flow.
12. Place the new TRV in situ, and run down the nuts by fingers (being sure not to cross the threads), and nip up the nuts. I did the CH pipe first so at least the rest of the central heating was sealed once this was done, as the valve was closed with the decorators cap.
13. Once both nuts are nipped up, a thorough drying of the area was done to ensure not a single drop of water was left. That way, if there was any water after the system was re-pressurised, I new it was fresh, and thus a leak.
14. Open the lock shield vale, the appropriate number of turns as in step 5.
15. Using the water fill connection, re-pressurise the system.
16. Check for leaks. Thankfully I have none!

Job Done.

The water in the bucket from changing the TRV was probably about 200-300ml. I'd say this is definitely a job any home DIYer can do. Simply be prepared and methodical. For example, the replacement TRV being ready to go straight in place. There is no point removing the old TRV then starting to mess around with jointing compound on the new TRV.