One Cold Radiator after drain and refill of system

29 Sep 2012
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United Kingdom

I've recently drained the CH system so that I could replace a damaged rad valve upstairs.

I've done this and refilled the systems - all the radiators upstairs and down are working bar one.

I've bled all the radiators (including the problem one) and I can hear water flowing into it as I bleed it (as water flows out of the bleeder I can hear new water flowing in - there is no air coming out the bleeder anymore).

The radiator valves on the problem rad seem to work ok (they're not TRVs). One note here - the problem radiator is the same rad that I used to drain the system (it has the drain plug below it) so maybe this could be the cause

Any ideas of what could be causing this single rad not to get warm?

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what type of system do you have? Does the pipe leading upto i presume a wheel head valve on the problem rad get hot?
Thanks for the responses!

Its an open system (with the expansion tank etc) - it is full now (after untying the float etc) and I can hear it filling up when I bled the rads (less now as hardly any air comes out of any of them anymore)

I'll try turn all the other rads off tomorrow morning and post the results

thanks again
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Well I turned off all the radiators I could (one has a seized valve - I tried until I felt the metal on the valve starting to give) and lo and behold the cold radiator has gotten hot!

I would never have tried that - thanks very much

Was this trapped air? And do I now turn all the rads back on?

thanks again
Probably just a bit of junk blocking one of the valves - the extra pressure of having the other rads turned off would have unblocked it.
May have been air but more than likely iron oxide deposits. By turning off all the other rads the water has no choice but to force its way through the blockage. luckily for you it worked :D turn all other rads back on.
:) Thanks everyone

Now to think about that seized rad valve...perhaps a battle for another day

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