Cold radiators

[Shiner68]

I would very much welcome any advice before having to call a plumber out; my problem is I have 2 rads (bedroom & ensuite) that won't heat up and I have exhausted my knowledge. I have carried out the following fault finding in an attempt to identify the problem but to no avail: With both rads removed, I have opened up the TRVs and Return Valves and I get hot water coming out of the pipework so I know hot water is getting to the rads. I then replace the rads, fill them up, bleed them, they heat up but then go cold and will not reheat again. Thinking the rads might be blocked I have given them a good hose pipe clearance in the garden and no sludge came out. I have even swapped the affected rad with a good one in the hosue and it works elsewhere so I know the rad is OK. With an affected rad in place, I loosen the return valve and the rad begins to heat up and draws hot water, at the same time, the other affected rad also heats up. As soon as I connect the return valve and tighten up all connections and re-bleed, the rads go cold. I am baffed as to what it could be (or just stupid and am missing something obvious?) All suggestions gratefully received, thank you.

 

[stem]

Try turning off all of the radiators in the house, except the two that aren't working. Sometimes when subjected to the full force of the pump it's enough to get the water flowing and clear any airlocks.

If the two non working radiators are close to each other, that would suggest to me that the problem is with the pipe supplying them. You may have drawn hot water into the radiator to fill it down one on the pipes feeding them, but there could be an airlock in the other pipe.

 

[Shiner68]

Thanks; The rads are adjacent (bedroom & en suite). I've tried your first suggestion, how else do I clear an airlock please?

 

[stem]

I assume that turning off all of the working radiators just leaving the non working radiators on, didn't work.

You could try it again and this time turn the pump onto max speed. Also make sure that the hot water is turned off so that the full force of the pump is operating on the non working rads.

Sometimes closing both isolation valves draining and removing the radiator and then opening the valves one at a time to let a full flow of water into a bucket can clear an airlock. Best done when the system is cold to prevent scalding. This assumes that your system has a header tank. You will of course loose any corrosion inhibitor in the water you let out.

It doesn't have to be an airlock, it could be a blockage.