Downstairs Rad Cold When Hot Water On

[JasonC]

I don't have TRV's on any of the Rads.

Surely if there was a blockage the radiator would never heat up, it wouldn't just be a problem when the hot water is on?

Also when I changed the pump on Saturday one of the original valves was stuck so I had to drain and refill the whole system - wouldn't this have cleared any sludge out? However it did take almost 2 hours for the system to refill - is this normal for a central heating system with only 3 radiators or is this related to the problem I am having?

 

[chrishutt]

Surely if there was a blockage the radiator would never heat up, it wouldn't just be a problem when the hot water is on?

Sorry, I missed that point. I think then it's a balancing issue. The hot water circuit may need restricting so as not to take so much of the available flow. Also I don't see why you need the by-pass open at all if you don't have TRVs. Closing that will improve circulation.

2 hours to refill the system is ridiculous, but may not be related to the main problem.