The conclusion of my question earlier this week was that a TRV on one of my downstairs radiators needs replacing.
I was advised by a friend that all that is required to replace it was:
Turn off power to boiler (to make sure pump is off).
Unscrew both TRV and valve to free radiator.
Tilt radiator into a bucket to empty it.
Remove dead TRV from radiator and fit new one.
Reattach radiator (TRV and valve) to pipes.
Top up system, bleed air, and go.
Is that he right procedure?
- How does the water from the radiator not flood the floor when he TRV and valve are unscrewed from the feeding pipes (at least until I manage to hold it above a bucket)?
- How come the water from the system (especially upstairs) not continue to flow through the now unattached pipes?
TRVs come in two parts, the top half contains the thermostat and adjuster and is outside the water system; it merely pushes and releases the valve. If the fault is in that you can simply unscrew the collar and replace it with a new one.
If the fault is in the valve (usually a stuck pin) you can try oil and pulling and pushing it with pliers. If that doesn't work (and it probably won't) you have to drain the system down to the level of the valve before replacing the valve.
You might be lucky and be able to replace just the head, since the valve body sounds to be OK. Most recent TRVs have the same thread connecting the head and the body (M30x1.0) but older ones might be M28x1, M28x1.5 (or is it 1.25?) or a clamp screw. The problem is that ordinary catalogues (Toolstation, Screwfix, etc) don't say what threads their valves use, and it's not obvious without taking the valve apart.
Does your old valve have a maker's name on it?
Andrew G is dead right about the stuff that comes out when you drain a rad: its opacity and permanence are directly proportional to the lightness of your carpet.
First thing to do is establish of this is a sealed system or a vented one with a header tank.
Starting from step 2, if you fully turn both valves off to the rad, you can then drain that rad. Unless you have fancy valves with included drain points, then you will need to do this at the union to the rad. Opening the bleeding valve on the rad will make it easier. As you crack open the nut on the union, water will leak out - you will need to catch this in something. Keep going till the rad is empty.
Now once the rad is empty you can focus on the TRV. If you have a vented system, then you will need to first block the feed and expansion and vent pipes on the header tank with bungs to create a hydraulic lock. This will stop air being able to flow into the system and limit the amount of water that can escape quickly.
If the system is sealed, you can open the rad valve (assuming it works well enough for that) and drain a few litres of water to release the system pressure. Once the volume of the expansion vessel has drained you should be in the same hydraulic lock state as with the vented procedure above.
Now you can undo the compression fitting that fixes the TRV to the pipe tail. Keep downward pressure on the head of the TRV as you do it, and relatively little water will escape (a couple of cups full). Beware that the water may be full of magnetite and that stuff stains!
Have the new one sat to hand ready to fit. When the nut is free of the valve, swiftly take the valve off, and stick your thumb over the pipe end. Then swiftly take your thumb off the pipe, and put the new valve on and apply downward pressure. Now hope that the protrusion past the olive on the pipe is not too long for the new valve, and that the old backnut fits the new valve. Lastly you can tighten the nut. The system is now water tight again.
Then the fun of reconnecting the valve to the rad. If you are lucky the new valve may fit the old stub in the radiator[1]. If not you will need to remove that and fit the one supplied with the valve. (many older fittings had a metal to metal cone joint to the rad. Many newer ones have a small pipe stub that goes into the rad, and another compression fitting to lock on to it on the valve).
Now you can unbung and refill or re-pressurise as required and fill/bleed the rad.
[1] The stubs in in the rads can be changed either by gripping flats on the outside of the stub with an adjustable spanner, or more traditionally, by using a large hex key designed for the purpose that fits up the valve stub. The new stub should be wrapped with a good quantity (15 turns or so) of PTFE before insertion.
That sounds like the actual valve bit is still working, and its just the TRV head that has failed. In which case its a much simpler swap since you may not need to touch the wet bit if you can get a new valve with the same or similar head.
Last time I did this I closed flow and return at the combi and closed all of the valves on the rads. There wasn't much water came out - if you're quick the TRV end of the rad. being disconnected can be blocked - so I didn't need to top up the inhibitor.
That depends on how lucky you are how many small tins you have and wheter you can plug the ends while you fiddle with the old and new bits of course. Its messy though I've seen people doing it. Maybe you could freeze the water with one of those mega expensive freeze the pipe kits. Brian
I can't understand why just refitting the head makes the radiator go cold. Is it just possible that the adjustment has been turned a complete revolution too far? What is the usual failure mode for a head. It would have to be that the inner part extends and this does not seem feasible.
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