Air in pressurised central heating system. Where from???

[DmitriyL]

Hello everyone.

A 2 y/o closed central heating system is working but is a continuing source of puzzlement for me.
One of the topmost radiators keeps accumulating gas of some kind. The system has been pressurized at 2.4bar and all radiators checked for air. 2 months on and the water pressure is 2.2bar + I have just bled gas in one of the radiators (nearly all height of the medium radiator).

I can't be drawing air from the atmosphere because the system is under a higher pressure. Right?
Can the system be producing gas from some sort of a chemical reaction?

Thanks.

 

[JBPHS]

One possibility is that the expansion vessel has lost its charge, allowing air to enter the system.

How old is your boiler? Has it been serviced on an annual basis if it is under warranty?

James

 

[DmitriyL]

One possibility is that the expansion vessel has lost its charge, allowing air to enter the system.

How old is your boiler? Has it been serviced on an annual basis if it is under warranty?

James

The whole system is 2 y/o inc boiler. Not serviced yet.
System has 2 expansion tanks (one small in the boiler) and 1 in the loft. Both have been tested for charge and are OK.

 

[Blagard]

Can the system be producing gas from some sort of a chemical reaction?

Probably from an electrolysis so yes. Adding an inhibitor to the system can reduce the problem

 

[Blagard]

Deleted duplicate

 

[DmitriyL]

Can the system be producing gas from some sort of a chemical reaction?

Probably from electrolysis so yes. Adding an inhibitor to the system can reduce the problem

What PH reading should the water read then? I do (supposedly) have Fernox inhibitor + leak sealer in the system.

 

[Diyisfun]

I had a problem like this & it turned out to be a small leak on a radiator.
I was bleeding the system every couple of weeks, until I found this leak.

 

[AdrianUK]

If there is no corrosion inhibitor in the system then it isn't air ..... its hydrogen!

The chemistry is that the water reacts with the steel of the radiators oxidizing the steel to form iron-2-oxide (the black sludge) and hydrogen by liberating the oxygen atoms from the water. It makes iron-two-oxide as distinct from iron-three-oxide, which is the normal 'rusting' process, because there is not enough oxygen available.

End of chemistry lesson

 

[ianmcd]

If your boiler is only 2 years old it is possibly still under manufacturers warranty, depending on the make you might void this if you add leak sealer, dont use it .

 

[JBPHS]

One possibility is that the expansion vessel has lost its charge, allowing air to enter the system.

How old is your boiler? Has it been serviced on an annual basis if it is under warranty?

James

The whole system is 2 y/o inc boiler. Not serviced yet.
System has 2 expansion tanks (one small in the boiler) and 1 in the loft. Both have been tested for charge and are OK.

How have the expansion vessels been tested if the boiler hasn't been serviced? Asking for specifics, with respect to you and sorry if this is not the case, but a lot of people incorrectly test the charge pressures.

If they are ok, as mentioned above could be a bi-product of corrosion within the system.

James

 

[DmitriyL]

One possibility is that the expansion vessel has lost its charge, allowing air to enter the system.

How old is your boiler? Has it been serviced on an annual basis if it is under warranty?

James

The whole system is 2 y/o inc boiler. Not serviced yet.
System has 2 expansion tanks (one small in the boiler) and 1 in the loft. Both have been tested for charge and are OK.

How have the expansion vessels been tested if the boiler hasn't been serviced? Asking for specifics, with respect to you and sorry if this is not the case, but a lot of people incorrectly test the charge pressures.

If they are ok, as mentioned above could be a bi-product of corrosion within the system.

James

The system pressure was quite low and when I was working in the loft I happened to pickup the expansion tank (on the flex pipe) and it felt empty. When I pressed the air bleed valve the air came out and the tank noticeably filled with water. This would imply that the other expansion tank has pushed the water up and into that second tank. Before prssing the air bleed valve I had measured the pressure using my nail-gun compressor and then I had filled it back to the same one as was before. Essentially the water was pushed between 2 connected vessels both of which had a way to absorb the force, thus at least the air bubble (if not the membrane had to still be intact). Later I had topped up the water with the feed valve and started observing gas formation...

 

[D_Hailsham]

The whole system is 2 y/o inc boiler. Not serviced yet.

You can forget about making any claim under the warranty. All warranties include a condition that the boiler is serviced every year.