Pump Pulling Air

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

Whitcop

Are the cold feed and vent connected within 150mm of each other into the 28mm pipe?

No. The feed pipe is connected to the 28mm return and the vent to the 28mm flow.

Whitcop

Thats now considered incorrect.The cold feed and vent should be connected on the flow just before the pump in the loft.The order is-Boiler,Vent Cold feed, Pump. The space between vent and feed should ideally be about 150mm.This config can be done with tee's or you could fit an air seperator.PS your boiler has done well

Combine them. Run the c/f into the o/v, cap off old cold feed and hey presto!

Mr. W.

misterdubya said:

Combine them. Run the c/f into the o/v, cap off old cold feed and hey presto!

Mr. W.

Click to expand...

I thought the boiler needed an overheat 'stat if using a combined feed and vent.

Thanks 45yearsagasman. Should the distance between the open vent and cold feed be more or less than 150mm?

Thanks Whitcop

Make it 150mm,but a 10mm either way will be ok.Don't combine the feed and vent as suggested,you boiler has no overheat.

Now that some milder weather has returned I have finally taken the plunge to fix the problem. I put bottle of flushing liquid in a few weeks ago and yesterday decided to alter the pipework as suggested.

Drained the system down. Moved the feed from the return to after the open expansion vent. While I was up in the loft I made a temporary change to allow the feed pipe to be connected to the cold water rising main. I then used the “mains” pressure to flush the system out. Then reconnected the header tank and refilled and added an inhibitor. The result is a quiet system and when I hold a container of water over the vent pipe no apparent suction.

Many thanks to you all and especially to 45yearsagasman for your help. Who knows maybe the boiler will go on for another 30 years!

WhitcoP