Recurring cold radiator

Horlock

Anyone got any good ideas why a radiator would be cold?

The radiator is in a rental house. We noticed it was cold when the old tenants moved out so.

1. I bled all the radiators.
2. I shut down all the other radiators and ran the central heating on full blast.
3. I bled this one some more - until eventually I got hot water out of this one.
4. Retested at this time and it worked.

Then just before the new tenants moved in (on another day), I rechecked all the radiators and they were all working perfectly (including this one).

Now it is a few months later and the same radiator is playing up again. Ie cold and not getting hot!

I can go to the house and repeat the process but I am wondering what could have happened to result in this situation recurring.

The only other thing which is very noticable with this radiator is that it bleds at a fraction of the speed that the others blead - ie I get a very faint trickle when fully open.

Really I'm looking for any advice - suggestions on causes or how to fix.

tony6403

Is the lockshield valve fully open ?

keystone

Try balancing the system.

Cheers

Alfrescodave

I also would suggest balancing the system - it may be that the tenants have "adjusted" your settings!!!

Horlock

Thanks for the suggestions - I hadn't heard about balancing a system before, so thanks for that suggestion - it certainly sounds hopeful - but relies on me managing.

As for the lockshield valve - yes that is fully open.

Two more connected questions:

1. Where would an attic valve usually be situated. I must confess I didn't realise there was one- as such I've never bled it. Therefore, it seems quite possible that there is air trapped! Preferably a more helpful response than "in the attic" - though I understand the temptation. Ie should I be looking by the hot and cold water tanks, by the eves etc etc - the attic has recently been insulated so spotting anything will doubtless be difficult. I have completely drained the system in the not too distant past - so I'm guessing that if I haven't bled this I could have serious problems. Generally speaking it would be sensible to look before asking a question like this but as I wont have internet access once I get to the house (an hour and half from home - it seems best to get as much advice as I can).
2. Could a pipe be blocked? If so is there anything that can be done? When I drained the system a couple of years ago. I did flush with cleaner and then put inhibitor back in the system. The pipes are thin - 8mm I believe rather than the more usual 10mm are ideal 15mm (I'm basing those numbers on my head rather than any measurements - by now I'm sure you realise that I am far from an expert).

Finally, thank you very much for the advice. Really appreciate it. I'm learning lots about central heating.

Final thing to mention is that the heating system is old (last serviced in 1993 - according to the boiler). I know there are some who would say "then replace it", but as we are looking to sell the house in the forseeable future and replacing the boiler almost certainly means replacing all the radiators and the pipe work it is not a financially good step right now - plus we can't really afford to anyway. So why mention it? Mainly because I don't really want to do things which traditionally cause boilers to go bang!

Thanks again to everyone.

Edit:

To answer question 1: The so called attic valve was situated in the airing cupboard, basically the highest point of the central heating pipes and just unscrewed by finger - it let out a lot of air.

Once again the radiator is working.