I've just finished installing an oil fired boiler in the kitchen to replace my old coal fired roomheater CH. It is now a fairly standard Y plan. Boiler is wall mounted in the kitchen. Pipes go up to floor space, horizontal for 2m then up into airing cupboard. Feed pipe then rises to vent into loft header tank and 4 inches along the cold comes in on the underside of the feed pipe.
Pipe then goes to pump, mounted to pump vertically. Next is 3 port valve arranged so it look like the letter T. One side to CH, other to top of HWC coil. CH return has non-return valve, then joins HWC return, then back to boiler.
So what happens is when CH switches off it seems that pump stops dead but water doesn't so I get a pressure surge on the pump inlet, where the vent pipe is. Water goes up the vent pipe and say a mug full goes into header tank.
To try to fix this I lowered the water level in the header tank - no good. Then I raised the vent pipe but the roof is low pitch so I could not raise this very far. About 21in is all I could get between water level and top of bend. Still not enough. I should also add that as I had a bit of 28mm spare and some fittings the section I inserted in the vent was 28mm which I thought would give the water more volume to take up before it overflowed.
Finally I tried a non-return valve. I already had a pipe connecting the CH feed to vent pipe via a gate valve (open gate valve to bleed air from pipework). I changed this for a no return valve which would open when vent pipe pressure was above CH feed, i.e. pressure across pump. When pump is on the pressure closes the valve. Better, perhaps, but I still get a trickle.
Suggestions?
Pipe then goes to pump, mounted to pump vertically. Next is 3 port valve arranged so it look like the letter T. One side to CH, other to top of HWC coil. CH return has non-return valve, then joins HWC return, then back to boiler.
So what happens is when CH switches off it seems that pump stops dead but water doesn't so I get a pressure surge on the pump inlet, where the vent pipe is. Water goes up the vent pipe and say a mug full goes into header tank.
To try to fix this I lowered the water level in the header tank - no good. Then I raised the vent pipe but the roof is low pitch so I could not raise this very far. About 21in is all I could get between water level and top of bend. Still not enough. I should also add that as I had a bit of 28mm spare and some fittings the section I inserted in the vent was 28mm which I thought would give the water more volume to take up before it overflowed.
Finally I tried a non-return valve. I already had a pipe connecting the CH feed to vent pipe via a gate valve (open gate valve to bleed air from pipework). I changed this for a no return valve which would open when vent pipe pressure was above CH feed, i.e. pressure across pump. When pump is on the pressure closes the valve. Better, perhaps, but I still get a trickle.
Suggestions?