Radiator gets hot at top and cool/warm at bottom

[jinkster]

I have a large radiator in the lounge that seems to get hot at the top and cooler or just warm at the bottom - it seems opposite to an air lock.

The system has been drained and new valve fitted - also all other radiators turned off and this is still the case.

Using a combi-boiler.

Any suggestions?

[giw12]

Sludgey stuff in the radiators maybe?

[eldar]

Sounds like not enough flow, are the valves fully open, and do other rads have the same problem?

[jinkster]

Other radiators seem to be ok.

No sludgy stuff when drained - seems quite clear to be honest!

[J-Tuner]

I had this problem in 2 radiators in my extension. The water that I drained off was black/dirty, so I removed them both and you should have seen the amount of sludge that came out once I flushed them through with a hosepipe!

If all else fails it's not that big a deal to take off and flush it through

[jinkster]

J-Tuner,

Did you drain both radiators? Last time I just drained the whole system.

[VxDuncan]

I had the same issues with a couple of my rads. Drained system, flushed a couple of times. No Joy. Ended up taking each of the offenders off and flushing them through with a hose. Lots of gunk. For the pipe work I attached a shower hose to one side (same thread!) and a threaded tap adapter for a hose pipe to the other side (again, same thread), and got someone to turn on the mains water into the system via the refill loop. The crap that came out of the bucket had to be seen to be believed! Good fun as well, especially when it's clear for a bit, then you get a big slog of black stuff, then clear, then black (little things)...

Bit of effort, but fixed the two none working rads and cheaper (/probably more effective) than a powerflush.

[Road2Ruin]

I have this problem at home with two very large radiators both over 3kW each. The issue I have is that they are at the end of the run and we have 8mm micro bore supplying them, which just cant supply enough flow to them. Consequently the water entering is hot but the water exiting is pretty much cold, the hot water rises making them hot at the top and cold at the bottom.

[Ricky_M]

Are both pipes leading to rads hot?

It may just be an air-lock in the return pipe.

If so, turn off all other rads bar those two, this concentrates full flow of the pump to these rads which should shift and air in the pipework.

[jinkster]

Road to Ruin,

I think this maybe the problem.

Any ideas how to fix?

[Road2Ruin]

Hi Jinkster,

If this is your problem then sadly there is no great solution. We were resigened to it and then about a year later had a new, more powerful, boiler fitted and it is a lot better. All I can say is make sure the heating water temperature is at or near maximum to make sure the water going in to the rad is a high as possible. Also make sure the radiators are balanced properly and the maximum flow is getting to the radiator.