Central heating system is Pressurised system with Combi-boiler. My fix attempts so far:

  1. Bleeding air out of the one radiator (with a bleed key). Immediately bled water implying no problem.
  2. Checked thermostatic valve (e.g. pin not stuck).
  3. Checked unbalanced system: in particular, I turned off all other radiators in my house to try and force a flow through the one radiator, but still it does not work.
  4. Flushed sludge from radiator: Took the radiator of the wall, took it outside and attached a hose to it to flush the sludge out - a lot of sludge was expelled so was hopeful this may fix it. Indeed when I reattached it to the wall, opened the valves to let the water through (as well as topping up the pressure in the entire system) the radiator got a little hot, but unfortunately quickly got cold (the pipes to/from the radiator also got hot then cold, perhaps indicating that the radiator is not requesting water?)

So I'm a bit stuck about what to do next - I'll likely try flushing the one radiator again to see if there is more sludge in there, but any help is greatly appreciated! :)

  • use a bucket and keep bleeding for few minutes to get the air bulb out
    – Traveler
    Dec 29, 2022 at 23:56

1 Answer 1


Turns out there was lots of sludge in the pipe to the radiator that was not allowing water to flow into it. Blasting this out using the pressurised system + loosening it with a long stick fixed it.

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