DIY Doctor UK DIY Forums

The hot water heating system has been working fine. The circulating pump started to fail so I replaced it with a new one. Due to the pump age a direct was not available so I was given a replacement that had slightly more capacity. The new pump has a 3 position switch to control speeds and I set it on the middle one. All went well, except the last radiator in the system was not getting hot. I decided to slow the new pump down and then the radiator got a bit hotter but still not to the top. I have tried your suggestions on balancing but still the same.

Any suggestions will be very welcome, as I am stumped as what to do next.

Not hot at the top could indicate air - have you bled the rads?

[quote="Steve the gas"]Not hot at the top could indicate air - have you bled the rads?[/quote]

Yes I did bleed the rads, several times and this is what is odd. With my old pump I always bled the rads with the pump running and the rads would then get hot to the top. With the new pump and running, no air came out at all !! I saw the suggestion that the bleeding should never be done with the pump running and so I tried that. Sure enough, air rushed out until fluid started to bubble out. I then tried the system, and sure enough it gets hot to the top.

So you were exactly correct, it was air in the system. Thanks for your help.