One radiator not heating up even after replacing both valves

8 Dec 2013
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United Kingdom
I have been following advice on other threads about one radiator not heating up but have still not had any success so wondered if anyone had any further suggestions.

I recently removed a radiator from the lounge (we had two huge radiators + the room was always plenty warm enough with just one on). I obviously drained the system to do this and when I refilled it there were a couple of leaks from the other radiator at the lockshield end which I sorted. I then tested the system and noticed the radiator wasn't heating up ... this has happened before with this radiator but has started working again a few days later so I thought the TRV was probably on its last legs. I drained the system again (cleaned it with cleaner first too) and replaced both the TRV and the leaky lockshield valve but still the radiator is not working. I have bled this radiator and all other radiators, tried turning all the other radiators off.

The pipe leading to the TRV gets hot but the pipe leading to the lockshield doesn't get hot. When I turn the other radiators off the pipe leading to the TRV cools down. I tried closing the lockshield and opening the bleed valve - this results in the pipe leading to the TRV warming up again but still no heat gets through to the radiator. I tried the same with closing the TRV and opening the lockshield but everything is cold then.

Not sure what to try next? Could the radiator be full of sludge (but it does drain from both sides)? Some sort of air lock even though I have bled all radiators??

Any suggestions would be great, thanks!
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If the return leg of the pipework is not heating up, you could have a blockage in it. I would turn both TVR and Lockshield off, drain the rad down and disconnect the rad. Then open the Lockshield up and see what type off water flow you have at it. Obviously have something to collect the water.
Thanks, I have just done that and it looks like you're right there's no water coming out of the lockshield even when opened fully and a wet and dry vac attached to the end. Is this likely to be air or something else blocking it? Any idea how I can unblock it? The pipe seems to go straight from the radiator into an external cavity wall ... ??possibly upstairs after that but not sure
It is unlikely to be air, so either the pipe has debris in it or has been crashed.
What type of pipe is it?
It is not uncommon for micro-bore pipe to become blocked if sludge is in the system and they also can be crushed easily!
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It's 15mm copper pipe. As far as I can tell this pipe only runs under the floor or inside the walls s I doubt its crushed. Guess it must be sludge then. Any way of removing this?
Jim, have a look at FAQ, look at both sets. You might be able too, with a bit of temp pipe work, pressure the system from the mains to flush out the airlock/sludge.
I would close all other radiator valves, connect a pipe up to the troublesome lockshield to drain off/flush out and then try push out any debri in that pipe section with mains pressure.
Have you removed the lockshield valve and poked something down the pipe ?

Usually a blockage is near the valve.

Mains water pressure might move it.

If water pressure is lowish then otherwise perhaps air pressure from a footpump if you can find a way to connect it.
Have you removed the lockshield valve and poked something down the pipe ?
Why would you advise to drain down and remove lock shield valve?...opening valve into a bucket will reveal whether or not pipework is restricted......either remove air vent plug and replace with a bit of tube or remove radiator.
Thanks for all of the suggestions. I've removed the radiator and fully opened the lockshield and nothing comes out. I then disconnected the lockshield and small bit of pipe from an elbow beneath the floor boards and nothing runs out of this pipe. I poked a piece of wire down the pipe and didn't feel any resistance until itgot to what I assume is an elbow after it enters the cavity wall.

I haven't tried connecting mains water yet... to do this do I just connect a hose pipe to the outside tap and then to the blocked pipe + turn on? Or do I need an outlet somewhere for the blockage to drain to? Our mains water pressure isn't very strong so perhaps a foot pump would be better? Although my concern with that is introducing more air in case it is an air lock ... Or do you think there's no chance of that being the cause?
i would want to flush it out. Will need a bit of messing around to do it. Does your system have the small F&E header tank? if so, I would use this as a place to pressure with the mains, you will need to isolate the Fill pipe, ensure the 3port valve is open ( switch off power and manually move to open position) as you do when draining your system. Then make a temp connection from the main into the Vent pipe. Now, with the help of a mate at the blockage and the rad disconnected but valves still in place, open the water main valve for a very short burst, ie open/shut! ( the valve at the blockage should be open before you open the water main, with said mate able to shut it after you have shut yours )
I would only use mains pressure INTO the blocked pipe.

Pressurizing the whole system risks creating leaks.

Jim did say that the rad did work but took a couple of days to heat. So, I would still try flushing out with the min of mains pressure, just a burst of mains would have been a better description.
I did not read it as working after a while but just totally cold!

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