Air in central heating pipes

[richig]

I have a small 3 bed semi detached house with 7 radiators and HW cylinder. The boiler is a Potterton suprima 30 (non condensing) – It is a Y plan, microbore (10mm) unvented system with combined feed vent and airseperater - all fairly standard for 1999 I think. The system has been great and the boiler always fires however. 2 months ago the system became noisy (whooshing/gargling) so we drained it down cleaned with X400, flushed and refilled with X100. Everything was fine but before we did this we noticed scum/spores on the surface of the tank (I pumped this out and cleaned the tank to avoid introducing it to the system). After this process everything was fine until a couple of days ago. Now there is the same scum in the tank and the same noise. I literally run the HW for 10 minutes and have loads of air in the system. I bleed the pump and the coil and all quietens down. Before bed I turn the water off, bleed coil and pump. Next morning, I beld the pump and coil again and lots of air came out. Now 12 hours after bleeding and with the boiler being off, where on earth did this much air come from? I no the water will have contracted as it cools but surely water would have dropped from the FE tank to replace this?



My personal thoughts are organisms in system – try AF10 or blockage in the air separator. the latter seems unlikely as the system does drain and refill easily and if the air seperater was blocked, surely this would not be the case.



I am very confused as to how this large amount of air is entering the system in such a short time when the boiler is off. I have checked for leaks including under the floor – the manifolds and pipes all appear fine and none are magnetic (including the air separator).



I would really appreciate some advice as to what is causing this!!!

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[ShaunCorbs]

whats did the water look like when drained and how did you fill the system

 

[richig]

whats did the water look like when drained and how did you fill the system

The water was fairly clear but it smelt very strong (yeasty smell)

 

[SimonG]

Corrosion.

 

[jtsplumbing]

May be that the cylinder has had it !

 

[Last Plumber]

Hold a cup of water under the vent pipe when the system is running with the surface of the water just covering/touching the end of the pipe. Only to see if it's drawing air in whilst the pumps on.

Just a place to start really. Rule it out !

 

[Ric2013]

Sorry, can't help, but don't know how to subscribe to a thread without replying.

 

[rpm]

Sorry, can't help, but don't know how to subscribe to a thread without replying.

Thread tools on the first Orange bar you find as you scroll up.

 

[Frog67]

Could be "Hydrogen" rather than air. This is a by product of the corrosion that can form in central heating systems due to all the different metals being in contact with each other. Flushing the system may have removed some of the corrosion but you may need to power flush it for a more thorough result. This is only a suggestion for your consideration

 

[Ric2013]

Surely if it's hydrogen, the fact that the OP bleeds it all out should sort it for a week or two. I'd be surprised if a large quantity could form overnight...

 

[Frog67]

i would start with the F+E tank. Bleed the system before bed and turn the CH/HW off. In the morning check the water level in the tank.
Could be a small leak in the system somewhere just enough to drain the tank which would also draw in air.

 

[devoncreamy]

a long time ago, we had problems with fernox inhibitor encouraging bacterial growth, change inhibitor, problem solved