Cold upstairs radiators

20 Apr 2014
Reaction score
United Kingdom
I have a micro bore system with an expansion tank in my attic. I have recently drained the system in order to put in Fernox sludge remover as a couple of my radiators had developed cold spots in the bottom. I did it exactly as advised i.e. tie up expansion tank ball cock, find drain point -I had two both situated in my garage, vent the upstairs radiators then the downstairs radiators to ensure system fully drained. I then added the Fernox, removed the ball cock ties and bled the air out of all the radiators starting downstairs then going upstairs. However, despite all of the above, all of my upstairs radiators remain cold now whilst the downstairs are hot! I have a motorised valve in the system attached to the hot water tank in my airing cupboard I have played with the thermostat on it and you can immediately hear water flowing so I believe this means that is working ok. In desperation, I have removed the vent plug from a small radiator in one bathroom which is the first to heat up normally and managed to connect a rubber pipe to it and left it to vent for several hours with the pump etc. switched off. Whilst doing this that radiator gets hot but as soon as I put the plug back in and switch on the system it goes cold again like all of my other upstairs radiators. I have now run out of ideas and would be extremely grateful for any further suggestions!
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First thing to try is turn off all radiators that get hot. Also have you got any bleed points in the system other than radiator bleed valves? (and the pump)
Thanks Oilman, I have tried switching off all of the radiators that do get hot but that has not worked. There are no other bleed points in the system. Wish I had never started... so much for preventive maintenance!

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