CH sucks?

[Axel]

My CH is getting air in it. Has been for years. I used to hav to regularly bleed an upstairs bathroom radiator. I recently put in bigger pipework so that I could turn pump down to 2 from 3, and that has stopped a lot of the air noises, and I can now open bleed screws without it sucking. But now it does this: Early in the morning, when the CH has been off for some hours, on switch on I hear gurgling of air bubbling up in my bedroom radiator. There is an F & E tank, but the CH is pumped. Interestingly, the CH has the pump on the return just before the boiler ( so it sucks the CH water around the system, but the HW pumps into the cylinder from the flow just after the boiler. I've checked most of the comp joints on valves etc, (although there are some old ones best not messed with).

Any suggestions of what to investigate and change, in reverse order of disruption of course!

 

[seco services]

circulating pumps never suck.

 

[mickyg]

Sounds like the system is badly configured. If its a fully pumped system it may be that its been the victim of a crude conversion from gravity at some point. The real answer is to identify the pipework layout and reconfigure it. Now I imagine thats not what you wanted to hear! You could always try turning the pump down to 1, it might help.

 

[Axel]

circulating pumps never suck.

I agree, but the net effect on the side of the system before the pump is that of suction - hence it is probably more likely to be sucking in air. I can reconfigure it one day when the weather warms up, but I believe there may be some advantages to be had with the CH pump being on the return...?

 

[seco services]

but I believe there may be some advantages to be had with the CH pump being on the return...?

what are they as i can't think of any

 

[Axel]

but I believe there may be some advantages to be had with the CH pump being on the return...?

what are they as i can't think of any

Something to do with avoiding pumping over in tank?

I'll draw a diagram when I've had a look at precise layout.

 

[seco services]

pump over will only happen if the pump speed is to high, sludge, badly designed system, blockage.