Open air vents

[patrickjoseph]

I have a fully pumped heating system with a 'Y' valve.
The system has always generated air from somewhere, but no obvious leaks exist.
My thoughts are that the open air vent, which is situated immediately before the pump, is allowing air to be drawn into the pipework by the pump.
Has anyone any experience of that problem, and is the solution to position the vent after the pump i.e. on the pumped side, or will that present other problems?

 

[45yearsagasman]

The open vent should not be just before the pump.
In order, from the boiler it should be Vent-Cold Feed-Pump in that order with approx 150mm between both pipes.
DO NOT fit vent after the pump.
View media item 32248This is how the feed and vent is positioned and is the same on Y or S plans.

 

[dcawkwell]

Or you could just cap the air vent pipe.
Sorted. Not right though. Just building regs that require it.
I just see the air vent as pointless.

It is acceptable to have no air vent if the system is under a certain size and you have a 22mm pipe feed though.

 

[simond]

The cold feed and open vent should be tee'd into the pipe as close together as practicable. 150mm is not the ideal spacing, it is generally accepted to be the maximum.

Reason being, water wont circulate between CF and OV if there is minimal pressure difference between them. So the closer together, the better the result will be.

Pumping over is normally caused by a pressure differential, this is commonly down to an accumulation of limescale based crud in the CF/OV area, only solution is to cut out and replace with new tube and fittings.

It is not considered acceptable to combine the CF and OV unless the boiler manufacturer gives their approval. Installers do it regardless though.

 

[45yearsagasman]

approx 150mm between both pipes.

I should have added maximum(I did say approx)
Combined feed and vent is another option as is fitting an air separator.
The first thing you should do however is to reconfigure the pipework so it is connected in the correct order.

 

[Boilerman2]

Lack of Corrosion inhibitor can also give the symptoms described, as Hydrogen gas builds up at the top of the radiators which needs constant bleeding - check your system for inhibitor and add Fernox Fi or Sentinel X100 as required!!

 

[Iddy]

Alternatively, the cold feed could be the teed in last on the return to the boiler...

 

[TicklyT]

Alternatively, the cold feed could be the teed in last on the return to the boiler...

Does that not depend on the boiler?
It was common practise for older boilers built with with gravity HW circulation in mind, but it isn't appropriate for a modern boiler which offers a higher resistance to circulation.

So changing the boiler on an older system without giving any thought to the cold feed and vent arrangements can lead to exactly the problems the OP has described.

 

[patrickjoseph]

I have a fully pumped heating system with a 'Y' valve.
The system has always generated air from somewhere, but no obvious leaks exist.
My thoughts are that the open air vent, which is situated immediately before the pump, is allowing air to be drawn into the pipework by the pump.
Has anyone any experience of that problem, and is the solution to position the vent after the pump i.e. on the pumped side, or will that present other problems?

SUCCESS!
Thanks for all the advice guys. I studied my layout based on the advice, and found that vent pipe was close to the pump but my cold feed was 'miles away' under the floor boards somewhere just before the boiler. So I T'eed off this cold feed just between the vent and pump, achieving less than 150mm between vent and cold feed, and everthing is now quiet and no air coming in.
Great advice, thanks.