I've read this forum with interest as I have similar problems. I also get air bubbles circulating in my central heating - they make quite a noise when they go through the thermostatic rad valves. The problem has become progressively worse over the last couple of years.
I have a suspicion that there's a hot spot in the boiler and I'm getting some localised boiling (it's an oil burner, open flue, and the internal design is such that the burner fires straight against the opposite internal wall of the boiler block, which must get pretty hot). When it's only heating the water (gravity, no pumped circulation) it certainly sounds as though there is some boiling going on and bubbles rising up the expansion pipe just after the boiler goes off on its thermostat. The thermostat itself seems to work ok and assuming that it is then I don't want to set it any lower as it's already a bit low on the lowest recommended temperature.
I'm thinking of one or more of the following:
1. Replace the boiler (just 10 years old) - presumably a new one will be more efficient and it would solve any boiling problem. Also, I've been told that conventional boilers may be increasingly difficult to get in future? But it's a bit of a sledgehammer to crack a nut.
2. Change the pump to a a variable speed / constant pressure variety. This would reduce the chances that I'm getting pump over into the expansion tank. (All rads have TRVs except one (which is a fan rad, doubling as residual open circuit for the pump), so when the house is up to temperature the pump is probably working too hard. But does a constant pressure pump work on a return circuit, which is where the pump is now?
3. Insert an air trap on the pumped outlet from the boiler. Although this wouldn't solve the root problem I'm fairly sure it would cure the symptoms. Does anyone know if such a thing exists?
Thoughts/comments/suggestions welcomed...
I have a suspicion that there's a hot spot in the boiler and I'm getting some localised boiling (it's an oil burner, open flue, and the internal design is such that the burner fires straight against the opposite internal wall of the boiler block, which must get pretty hot). When it's only heating the water (gravity, no pumped circulation) it certainly sounds as though there is some boiling going on and bubbles rising up the expansion pipe just after the boiler goes off on its thermostat. The thermostat itself seems to work ok and assuming that it is then I don't want to set it any lower as it's already a bit low on the lowest recommended temperature.
I'm thinking of one or more of the following:
1. Replace the boiler (just 10 years old) - presumably a new one will be more efficient and it would solve any boiling problem. Also, I've been told that conventional boilers may be increasingly difficult to get in future? But it's a bit of a sledgehammer to crack a nut.
2. Change the pump to a a variable speed / constant pressure variety. This would reduce the chances that I'm getting pump over into the expansion tank. (All rads have TRVs except one (which is a fan rad, doubling as residual open circuit for the pump), so when the house is up to temperature the pump is probably working too hard. But does a constant pressure pump work on a return circuit, which is where the pump is now?
3. Insert an air trap on the pumped outlet from the boiler. Although this wouldn't solve the root problem I'm fairly sure it would cure the symptoms. Does anyone know if such a thing exists?
Thoughts/comments/suggestions welcomed...
