Pump Pulling air

[Whitcop]

My heating system was installed in 1981 when the bungalow was built. It consists of a wall mounted Ideal Concord WCF 255A boiler with the flow and return (28mm) going up into the loft where the pump and 3 motorised valves are fitted (I think it was called an S plan plus). This allows separate temp and timer control of the living rooms, bedrooms and HW. In the attic a feed / expansion tank is fitted approx 1.2m above the pump and valves. There is a 15mm cold feed from the tank that tees into the 28mm return just above the boiler and a 22mm open vent (over the tank) that tee’s off the 28mm flow just before the pump.

The original pump was changed for a Wilo 15/50 pump about 7 years ago. Over the last few weeks I’ve noticed that the pump seemed to be getting very noisy so last week I changed it for a Wilo Smart pump and I’m running it on it’s slowest setting. The hole system is very noisy and I’ve noticed that the pump is pulling air in through the open vent pipe (I held a container of water over the end) and air is collecting in the rads which need bleeding each day. Any ideas why this should start happening? Can I blank off the open vent and allow the boiler to vent back through the cold water feed pipe?

Thanks

[FONT=&quot]Whitcop

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[PlumbBobBob]

on no account blank off the vent it's there for a reason. possibly the pump is the wrong way round so pulling not pushing round the system.imho

 

[washer]

If there is room, you could remove the cold feed from the return and T it in between the pump and open vent, this will stop it drawing in air.

You can only have a combined feed and vent pipe if it is run in 22m and the boiler has an overheat stat, which yours doesnt.

 

[WHPES]

System could be sludged up.

If it isn't, an easy cure is convert to a sealed system.

 

[fuzzy]

sucking in air, is it the wrong way round? i presume it aint always been like this. also check for sludging