one rad not working

[pppp7373]

hi yea, we got a new extn and 2 new double rads fitted, one always was just luke warm, after reading all the post here i turned of all rads but the cold one, then turned back on the rest and all are holding there temp, now when i went to turn the boiler on i found that the temp nob was at its lowest ,would this be why the rad never heated

thanks paul in dublin

 

[stem]

No, the temperature knob controls the temperature of the water flowing around the system. Therefore all radiators should be at the same temperature. ie all hot or all warm according to the setting.

One radiator that is different to the others suggests that either the system is not balanced correctly, or there may be a partial blockage or air in the system somewhere. If either of the latter two you may have cleared it.

If the problem persists I would try to balance the system. Plenty of info on here as how to go about it.

Sometimes sludge build up in a radiator can cause similar symptoms, but only in older radiators that haven't been treated with corrosion inhibitor.

 

[D_Hailsham]

Not really. Turning the boiler temperature down just means that all rads will be cooler.

It sounds as if the system was not balanced after the new rads were installed. This is done by adjusting the lockshield valve (LSV) on each rad (opposite end to the TRV or wheel valve) so the temperature drop across each rad is the same.

You will probably find that the LSV is fully open on the new rads.

Detailed balancing instructions are here.