One radiator not heating up after balancing and a drain/refill

[D C]

This is a frustrating one!

Radiators are spread over 3 floors, one on the ground which is right next to the boiler (Worcester Bosch Greenstar 30si), 4 rads and a towel rail on the second floor with one rad currently disconnected for (very slow!) decorating, then 2 rads and a towel rail in the loft that were fitted about 4 months ago.

When the loft was finished the radiators and the towel rail there worked fine, but now only the radiators are getting hot and the towel rail stays stone cold. So far I've tried:

* Balancing the radiators by closing the lockshield on them all except for the towel rail

* Sticking a hose on the bleed valve of the towel rail and draining out any air (there was a bit in there) to remove any lock, after which it heats up....then goes cold again

* Draining and refilling the whole system. Again, it got hot straight after filling and stayed like that for the evening then back to cold again.

As far as I know, the two upstairs radiators and the towel rail are all on the same loop so how can two of them get consistently hot yet the towel rail stays cold? Both valves on it are wide open and I can't even feel the pipes to them getting warm. This has been going on for about 2 months now but the cold snap has focussed my mind a bit!

 

[PrenticeBoyofDerry]

When you drained the system down, how clean was the water?

 

[D C]

Pretty clean. The system was power flushed when the boiler was fitted about 2 years ago, there's dirt in there for sure as when the magnetic filter was last emptied it had a load of crud on it, but when I drained it it was all clear.

I'm wondering if when I balanced the rads I shouldn't have shut down then quarter turn opened the lockshields on the top floor (same loop as the one that's not getting hot), is that likely to make any difference?

 

[D C]

Right forgot to post back on this, it was what I guessed at - closing down the lockshields on the other two radiators on the top circuit (which I'd done because the things were banging away at 5 in the morning) somehow stopped flow to the towel rad. I opened up the lockshields and hey presto, hot towels again!

That's what I get for trying to be "smart" I guess!