One-pipe heating system, one radiator barely warm

[BonnieR]

I have a one-pipe heating system. The master bedroom radiator becomes just vaguely warm with a hot but not burning pipe at the inlet and a cold pipe at the outlet.
Local heating guy says "It must be at the end of the series, that's just how it is." However, I think that may not be the issue as my child's bedroom gets far too hot.
I can not see that I have any TRV's on the radiators, just plain valves presumably for opening or closing the radiator which we were told not to adjust. Also, bleeding the air out of the radiators made me feel better but did nothing noticeable to improve the situation.
Can someone help? Thanks.

 

[Armo74]

Sounds like a balancing issue, The system needs balancing correctly. The trouble with a one pipe system is that the last radiator will end up with all the cooler water from all the other radiators as the water goes in through the flow and comes out through the return at a cooler temperature and then on to the next radiator and then eventually back to the boiler.

 

[BonnieR]

Can you recommend how I might go about balancing the system?

 

[doitall]

Nearly right Arno but not quite.

First plan would be to take the problem radiator off and flush it out with a hose.

 

[Armo74]

Look in the FAQ's there is an explanation in there.

 

[doitall]

The valve should be fully open unless you have special tee's/fittings.

If the water is circulating the loop then it will go into the rad unless some thing is stopping it.

 

[BonnieR]

Thank you for your responses.
Is it possible that the valve into the radiator is blocked? Would need to remove that radiator to check? Also, is it possible that the hot bedroom is too hot because hot water is blocked in??

 

[Armo74]

I stand by my first post if you say the problem radiator is luke warm all over. But we can't be right all the time Providing of course you have the valve on the flow pipe fully open.

 

[BonnieR]

The radiator does vaguely warm. I suppose all over, though on a cold day one can't even feel its warmth.
Regarding rebalancing, I've read the FAQ on rebalancing the system. It seems quite logical, however all I have are wheelhead valves on some of the radiators and the bit for clearing/draining on the other end.
Thanks again for your advice.