Diagnosing lukewarm radiators.

11 Dec 2005
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United Kingdom
I have two column rads at the far end of my CH loop that take forever to become even lukewarm despite inlet pipe temp at 50⁰+.

Plumbers have installed bottle air vents in case an airlock was the problem but to no effect. I've drained the system, checked pipes for blockage - all fine. Reversed the flow - still same problem. LSVs are wide open. Bleeds are fine. Someone suggested rads might be the issue (either airlocking, blocked or upside down?).

I would like to shut the manual wheel valve and LSV on each rad in turn (to avoid draining system again), fit a cheap steel rad and see if that heats up but I need two flexible pipes to connect between the existing valves and the cheap radiator. Do these exist? Not even sure what to search for as I've found nothing yet. I'd need a 1/2 inch male thread at one end and a female 1/2 inch for the valve. Otherwise not sure what else to do.

Really hoping that will shed some light on the problem.
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