Have a radiator that is not warming up properly. All the other radiators in the system are too hot even to touch for anything other than a moment but not this one. I bled it and there is no air in it. It does get slightly warm, but given the performance of the others, something is amiss. I even removed the TRV completely but this doesn't change anything.
Any advice?
TRV plungers can get sticky. I generally tap the body of the valve and use a pair of side cutters (because that's usually all I have to hand) to grip the "plunger" to make sure it's coming up, and the flat side of the cutters to press the plunger down. A bit of up and downing and tapping of the valve body frees it up.
:)
Has it ever worked or is this a recent thing? When you say you removed the TRV completely, did you just remove the top half, the bit with the waxstat in, or the whole thing complete with valve?
Two suggestions: first, if it's never worked, the lock-shield valve may be shut. That's the manual control at the other end of rad from the TRV. You need to unscrew the domed cap (if it has one) and try turning the spindle anticlockwise with e.g. a mole wrench, or a spanner across the flats if there are any.
Second, the valve part of the TRV may have seized in the shut (i.e. down) position. Simplest solution to try is to remove top section of the TRV, grip the pin with pliers and try pulling it up. If it shifts, work it up and down to free it and perhaps lubricate the shaft with some high temperature grease. Failing that, a total replacement of the TRV.
Air lock in pipe to the radiator? Turn off all other radiators and turn up the pump speed to see if it gets hot.
Then put everything back to where it was previously.
If now it still doesn't get hot you need to balance the system. Water will take the path of least resistance. Tweak the lock-shield valves on the other radiators to throttle the flow by a small amount.
Could be an air lock or blockage in one of the pipes. Assuming that you're satisfied that both the TRV body and the lockshield valve are working properly, try bleeding quite a lot (maybe a litre) of water out with one valve open and the other closed. Then swap over and do it again. This will ensure that both flow and return pipes are clear - or provide some clues if nothing comes out in one of the bleeding operations.
Another thing to try is to turn off all the other radiators, and turn the pump speed up - so see whether that clears whatever is stopping this radiator from working.
If it then works ok, but goes cold again when the other rads are turned back on, it indicates that the system needs balancing - i.e. the hottest rads need to be throttled back by partially closing their lockshield valves to ensure that the problem one gets its fair share of the flow.
Is it a microbore system? I have a similar problem with one rad. My CH man lives on the same estate(Redrow, between 15 ~& 20 years old) and says that (as I saw when the house was being built) the pipes are between the blockwork and dot n dab pboard. The bends are sharp 90deg elbows rather than swept bends and are probably partially blocked. Flushing and inhibitor have helped but the only cure is, when there is a major redec to remove the pb and replace the bends :-(
Malcolm
On 11 Mar 2016, Rob grunted:
Airlock somewhere?
Worth trying shutting off all the radiators on the system except the duff one, to see if that clears it.
When you say 'there is no air in it' I'm guessing when bled water comes out?
I ask because that's exactly what was happening to a mates rad (a plumber ironically) who said 'one rad was only getting half warm, he had bled it but it hadn't helped'. I released the bleed screw (the key was still in it) and heard / saw nothing. I took the screw right out, still nothing. He found me a bit of thin wire and I poked that into the valve hole and 'hey-presto', instant hissing and I just had enough time to get the screw back in before we got to water (I did have a rag handy). ;-)
Cheers, T i m
I have a microbore system and have a couple of sluggish radiators. I had a third one re-piped when I was having some alterations done. The pipes were clear - but the blockage was where the flow joined the manifold. Unfortunately I wasn't around to arrange to have the other connections cheched and it is now platerboarded over.
How do you test for that?
It was a failed lockshield valve the last time I saw this problem.
Fair comment. But if, with the TRV open and the lockshield closed, you can bleed water out but the other way round nothing comes out, that indicated that there is a problem on the lockshield side - either with the pipework or with the valve itself.
Maybe, in retrospect, the bit you queried didn't add any value to my previous post.
Maybe you have not seen a dropped lockshield valve.
Probably not - I handle mine carefully.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.