Problem with single cold radiator, that I thought I had fixed

[ijabz]

I have just had the heating back on for about two weeks, all the radiators have been bled but one remains cold and the pipes to and from the radiator are also cold, I am a diy novice, and give as much detail as I can think off in the hope somebody has a simple solution. The radiator is a standard type with a lockshield on the left handside and a themostatic valve at the right hand side. I thought that maybe it was full of sludge so I took it off today and although the sludge didnt seem that bad I took it outside and flushed it with a power hose until thoroughly clean. I then thought I check the that the valves were working so I turned on the thermostatic valve but no water came out as I was expecting (the central heating was on) but I wasnt sure if it was meant to so I then put the radiator back on and opened up the lockshield and thermostatic valves. Imediately the radiator started heating up, this got me thinking that maybe the radiator was filled from the lefthandside which seemed the wrong way round but I wasnt too concerned because the radiator was getting hot, I bled the radiator as it filled up and 90% of the radiator got very hot except the top right hand side (above the thermostatic valve), however i never got to the stage when water came out of the bleed valve, it just stopped bleeding air.

Then I checked it about half an hour later, and was disappointed to find it was cold/lukewarm throughhout and the pipes to and from the radiator were also cold, what has gone wrong ?

thanks Paul

[Sparks]

What type of system do you have?

Sealed - You will have a pressure gauge near or on the boiler and a filling loop (Flexible pipe connecting between the mains water and the central heating pipes (usually near the boiler) If so, you need to add more water to the system (Removing the radiator, then refilling it will have depressurised the system)

Or do you have a vented system - this has a small water tank in the loft to keep it topped up.

If so, try and bleed the radiator again, if no joy, check this tank has water in it!

As for your not getting hot problem...

Sort the system out so you can bleed the offending radiator first, then try and remove the head of the thermostatic valve, there is usually a ring at it's base you unscrew, this will enable the head to come off to reveal a pin (Water shouldn't leak out when you remove the head!) - does this cause the radiator to get hot - if so, the head needs replacing, if not I would guess the valve is knackered.

As a lat resort you can try turning off all the other radiators in the house, set the system to heating only (If you have a hot water tank) and see if that sorts it.

Sparks...

[Sparks]

I forgot to say, if your system is sealed, it should be at around 1 bar when cold.

Sparks...

[ijabz]

Thanks for quick reply

It is a Vented System ( probably 20 years, small copper pipe connectors). i think I see where youre coming from with the bleeding, there may not be enought water in the system to fill the radiator, even after removing the air, i think I have had this problem from time to time with other a few other radiators when I have bled them (although they stayed hot), I wil check this first thing tommorrow.

Ill then see if I can remove the head of the valve, I assume what is a happening is the radiator is getting hot but then the valve is calculating the temperature incorrectly and telling the radiator to cool down again ?

[Sparks]

Possibly, but as you said in your original post, "I turned on the thermostatic valve but no water came out" I expect the head or valve is broken/full of crud - Did you turn it full on?

I expect the heating while filling was due to the rad filling via the lockshield, I assume you had the heating on at this point, if so, it would be filling with hot water ;-) but it would go cold soon if there wasn't any water circulating in or out via the Thermostatic Radiator Valve (TRV)

If either of the valves are off, then the rad will fill from the other, even if it is normally the outbound flow valve.

You just said "It is a Vented System ( probably 20 years, small copper pipe connectors)" How small is small?

If this rad was sludge up, then there could be a plug of crud blocking the TRV - this may be pushed through if you turn off all the other rads in the house and leave this one full on (on the TRV and the lockshield)

Do you have any inhibitor in the system - you really ought to!

Sparks...

[ijabz]

Thanks very much Sparx, the problem appears to be solved, Ill explain what exactly I did in case of use to other novices

I tried turning off all the other radiators, I couldn't turn off the hot water because the central heating only works when the hot water is on, no change, i then tried bleeding the raidator no air or water came out at all.

I then went up into the loft and there was plenty of water in the expansion tank (it was 3/4 full), I also checked the temperature it was warmer than I expected 25%Celcius, but this matched the temperature of the loft so i guess that is alright, there was also quite alot of noise from the pipes going into the expansion tank.

I then look at the thermostic valve, our is mounted horizontallly rather than vertically. I Unscrewed a screw and was then able to pull the head off. Underneath was a nut with a pin in it, I wasnt sure what to do so I unscrewed the nu a bit and then took it completely out, a little bit of sludgy water came out but nothing else much happened. I then tried twisting the pin with a pair of pliers, suddenly it popped out about an extra 5mm and the radiator started getting hot at that end immediately I bled the radiator and the air came out much more quickly this time, and I now have radiator that has ben hot for an hour now !,

The pipes are 10mm diameter I guess this makes them more suspectible to sludge, I did think about using corrosion inhibitor but I was worried about using it because I had read it can make the early signs of corrosion worse, also I was not really to sure how to train the system properly, we dont have any draincocks and I was worried about introducing airlocks.

Paul