One hot radiator, all others lukewarm or cold

13 Jan 2005
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United Kingdom
My gas boiler is downstairs. The hot water tank and pump is upstairs. The radiator in the bathroom is very hot (though this is not the one closest to the pump). All other radiators (upstairs and downstairs) are lukewarm or cold (warmer at the top than the bottom, I've noticed). Hot water is fine.

What could be my problem ? Something to do with the pump ?
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Mostly likely you need to balance your radiators. All the water is flowing through the bathroom radiator and not to the rest. There are post on here about balancing so try a search, but basically close the lockshield valve (the one at the other end from the normal valve. From how you descibe it I'd close it fully then open it 1/4 turn, perhaps 1/2. See how that works.

Next identify any others that now are much hotter than the rest and do the same with them. The aim is to get all the radiators equally hot. To get it right you'll need a thermoter and a lot of time, but just closing the worst ones should make a big difference.
I'll try that - thanks. But why would it change so suddenly ? A week ago all radiators were hot.
You didn't say that.

You could have sludge build up. You can add cleaning chemicials, then flush and refill with fresh inhibitor. See screwfix and X400-X100, or fernox web site. Or you can have someone power flush the system - expensive. Or you can take the radiators into the garden and hose them out.

You pays your money and takes your choice. Personally I start at the cheapest and work up :confused: .
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Another thing I noticed: Starting from cold (in the morning), the radiators get warmer and warmer until almost hot, then after 20 minutes or so get cooler and cooler, never to warm up again until the next time it starts from cold.

The pump seems to be vibrating and humming quite nicely, but still only the bathroom radiator gets hot (though someone suggested this could be because it's on the hot water circuit rather than the central heating circuit, so this could be a red herring). I've adjusted all my lockshields as suggested.

Does the sludge theory still apply or does this new evidence point to something else ?
... oh, and I don't have a room thermostat, so it can't be this forcing the radiators to cool down.
What CH do you have? Gas, oil, coal? How old? Does the hot water need the pump to be on (is there a HW thermostat, time clock, etc.)? Are there any motorised valves? Do the rads have TRVs (thermostatic valves)?
Turns out it's the motorised valve not functioning correctly.

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