Heaters cooler at the bottom half

[dumbhusband]

Three out of our 12 heaters are cooler at the bottom that at the top. We power flushed the system as advised, but the problem remains. In addition, these radiators were separately taken down and washed down with a hose separately.

As an experiment, I switched off ALL the heaters and then switched on each of them independantly (fully turning both valves). The problem disappeared with two of the radiators.

When I turned on all the heaters, the bottom half of these radiators cooled down.

Don't get me wrong, they are still hot, but noticeably different from the top half.

Any ideas of what could the cause be? Is it the pump? is it just a more delicate balancing act? Do I need another power flush?

Any advise would be greatly appreciated.

 

[jimbox]

these are normal radiators right? they are fed from the bottom?

does it actually matter? i mean, are the rooms with these radiators noticeably colder than the other rooms?

 

[EliteHeat]

It would be normal to have about 11 degrees difference between top and bottom. Do you have more than that?

 

[dumbhusband]

Well, it does to the wife.

On a serious note, yes, they are normal rads and it is noticeably different in the one room with the two "faulty" radiators.

As for the 11 degrees difference, I thought it was between the left (inlet) and right (outlet) rather than the top and bottom. If this is the case, this I can comfortably narrow the problem down to one radiator.

I am tempted to just replace them with three new rads. any thoughts? My theory is that there is limescale in the rads and the power flush cleaned everything else out

Thanks again for your advice

 

[discoverer]

I had a similar problem. The difference between temperature of top and bottom on a couple rads was quite big so was advised to fit a new central heating pump which worked great and solved the problem. If you have added radiators you can fit a slightly larger capacity pump Grundfos 50/60 or similar.

 

[dumbhusband]

Thanks, this was my initial gut feel as I had to increase the pump from 2 to 3 to actually heat the affected rooms.

British Gas are coming to inspect our system before agreeing to insure us for the year, so will wait to get his formal report and carry out all the required work at once.

I will update this forurm with his findings.