Air in pipes - no logical explaination?

[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 - 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!!!

 

[flameport]

Blockage causing water to be pumped through the vent into the expansion tank which will incorporate vast amounts of air.
or corrosion inside the system, in which case the 'air' will burn when a flame is applied to it.
or both.

 

[richig]

Blockage causing water to be pumped through the vent into the expansion tank which will incorporate vast amounts of air.
or corrosion inside the system, in which case the 'air' will burn when a flame is applied to it.
or both.

Forgot to mention it is a combined feed vent. The water in FE is always cold.

 

[Nige F]

Micro air leak on the suction side of the pump ?

 

[richig]

Micro air leak on the suction side of the pump ?

Thanks, any easy way to diagnose this?

 

[gasmanstu72]

Thanks, any easy way to diagnose this?

turn off the heating and hot water for a while so the pump stops running and check for leaks on the negative side

 

[Nige F]

or even marks from old leaks - build up of crud outside of joints.

 

[Steelmasons]

You have a vented system as opposed to unvented..

 

[Agile]

Blockage causing water to be pumped through the vent into the expansion tank which will incorporate vast amounts of air.
or corrosion inside the system, in which case the 'air' will burn when a flame is applied to it.
or both.

As he said it is an unvented system then it is very clever to diagnose that he had wrongly described it.

Where did you buy your crystal ball?

 

[slippyr4]

Where did you buy your crystal ball?

It's not his crystal ball, but his glasses:

I no the water will have contracted as it cools but surely water would have dropped from the FE tank to replace this?

and

Forgot to mention it is a combined feed vent. The water in FE is always cold.

 

[Agile]

Right, yes, the conflicting information!

The concept of "water dropping from the EE tank" tends to make the whole sentence rather suspect.

 

[Scarum]

Did you properly flush out all the X400. I would say three refills and flushes of system is seen as "proper". At least that's what I did when cleaning glassware in a laboratory.

Re scum, same thing happened to me too. My old lid to the FE tank was not ideal or tight fitting, I had wondered if a mouse had fallen in but thankfully after baling all out there was no sign of rodent swimming activities. AF10 smells just like Jeyes disinfectant, I wonder if the latter would be OK to use in its place as it is a bit cheaper and easier to find on the high street. Just a thought.

 

[oilboffin]

You could try a weak solution of bleach leave it in for couple of hours then rinse