I have de-sludged and drained down, and still have cold rads

[D_Hailsham]

I bled the radiators when the pump was not running , but no air came out of any of them.

I also emptied a bucket full of water from the FE tank and bent the float down so water level is now about 1 or 2 inches above the feed.

That's good

I have just turned off all rads, I closed TRV and LSV on each, leaving one open on the ground floor. There was a lot of gurgling and big knock and a rush of hot water up the vent pipe and into the FE tank. I did this to all 5 offending radiators but none of them even got warm.

Water going up the vent pipe into the F/E tank is called Pumping Over

It is pumping downwards, and the vent and FE pipe are above the pump on the inlet side.

But, as Grundfos say, pumping downwards can lead to problems. I notice that the vent pipe is in line with the riser, which means that the water has to go round the bend of the Tee to get to the pump. It is considered better practice to have the main pipe horizontal with the vent going up from this using an inverted Tee.

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• D_Hailsham
• 24 Nov 2008
• 2