Oil boiler (now~15 years old) unvented system with 17 radiators. We moved in 5 years ago and I had to keep bleeding the same radiator. The bleed gas could be burned with a blue flame and the water was acidic (pH 5.5).
Since then system has been chemically flushed (it was not too bad) and the radiators balanced (all the lockshields were fully open) but by last summer the pH was acidic once more. It has since been flushed and has remained alkaline all through winter. But still I have to bleed one or more radiators every 6 weeks or so (small radiator is about half full of air). There is no pressure loss (constant at 1.5 bar) and the expansion vessel is constant at 1.5 bar when cold. So, with no pressure loss, there is no water leak (leak sealant was added at last refill) but still the air keeps coming. It is also no longer combustible, so not hydrogen.
After the last bleed of every radiator, when I turned the heating on I could hear a small amount of gas circulating around the boiler area. During the bleed, there were very tiny bubbles in the radiator water. I check radiators periodically in the weeks after bleeding and they all seem to be OK, and suddenly one is very bad like the air has just moved there in one go.
Any ideas/advice on the source of the air? Can the pump be pushing air in without leaking water? I cannot understand how air at 1 bar can get into a system at 1.5 bar.
Since then system has been chemically flushed (it was not too bad) and the radiators balanced (all the lockshields were fully open) but by last summer the pH was acidic once more. It has since been flushed and has remained alkaline all through winter. But still I have to bleed one or more radiators every 6 weeks or so (small radiator is about half full of air). There is no pressure loss (constant at 1.5 bar) and the expansion vessel is constant at 1.5 bar when cold. So, with no pressure loss, there is no water leak (leak sealant was added at last refill) but still the air keeps coming. It is also no longer combustible, so not hydrogen.
After the last bleed of every radiator, when I turned the heating on I could hear a small amount of gas circulating around the boiler area. During the bleed, there were very tiny bubbles in the radiator water. I check radiators periodically in the weeks after bleeding and they all seem to be OK, and suddenly one is very bad like the air has just moved there in one go.
Any ideas/advice on the source of the air? Can the pump be pushing air in without leaking water? I cannot understand how air at 1 bar can get into a system at 1.5 bar.
