Some radiators hot some cold

29 Oct 2010
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United Kingdom
Some of my upstairs radiators get hot whilst others stay cold. All rads apart from 2 myson towel rads have Honeywell Radplan thermostats fitted. The 2 Myson towel rads heat up fine, as do 2 of the other rads but the remainder are cold or luke warm at best. I've tried setting all thermostats to max but it doesn't change anything.
The upstairs heating is independent from the downstairs which is underfloor. I have a mains unvented system with an oil boiler.
Any advice would be appreciated.
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Try, turning off the rads that do work and leave on the ones that don't work, that normally, gets them going again.

Failing that, if the broke rads have TRVs, on they can over time get stuck, try moving the setting from 0 to 5 a few times, or unscrew the head, and useing waterpump pliers try and free the mechanism, (a small pin) using works
I've tried turning the hot ones off but no difference. Also tried turning stats on and off but still no change.
House is only 7 years old as are rads and pump.
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I agree with Ben, sounds like cr.p in the system. Systems with UFH are prone to a bacterial build up if has not been treated. So you could well need a clean out. Just ensure you get someone in that knows what they are doing!!! Cleaning UFH systems need specialist cleanser & you don't want some 6 week course cowboy knackering your UFH pipes. So take care.
Just ignoring "Richie" is probably best; he is not a RGI, but a notorious troll.

Try turning ALL hot radiators off, and makes sure there is NO flow through the cylinder coil.
I was an RGI when you were still in shorts mate. And what does being an RGI got to do with UFH anyway???!!
I have turned all hot rads off. How do I check that there's no flow through the coil?
Find the zonevalves or 3-port valve and check that the pipe going to the cylinders is cold.
If it's a bacterial crud in your system it'll be so of slimey gunk. Get someone that's in the know to have a look at it.
Right, all the previously cold rads are now hot and the previously hot rads that I turned right down earlier are obviously cold. Is it just a case of adjusting stats all round now to required level and thus end of problem?

Thanks for all the help and advice guys :D
Feel the bottom of the rad, between the valves (with due care, can be hot )
If the middle is less hot than the sides, system needs cleaning.
If not that, it is either the pump or unbalanced system.

Always running the DHW at times when you do not need the CH and vice versa will also give a much improved performance.

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