Hope somebody can help with this!
I have a conventional system, heat-only boiler, F/E tank, HW cylinder, diverter valve. Upgraded an earlier system in 1998, plumbed boiler - open vent (22mm) – cold fill (15mm) - pump. Open vent and cold fill are the recommended 150mm apart. Cold fill up-and-under. Both pipes go straight up to the F/E tank.
When I retired in 2010 I did some improvements including fitting a Magnaclean and changing the galvanised F/E tank for plastic. There was some sign of water coming out of the open vent, so I lengthened it to 750mm above the water in the F/E tank.
I’m fairly sure it was OK after that (no more water coming out of the vent).
Earlier this year the pump (Grundfos 15-50) was getting noisy, so I changed it for a Grundfos UPS 2. Everything seemed fine, but the other day I happened to feel the pipes and the open vent and cold fill were hot. There was a steady trickle of water from the open vent.
The vent outlet is brought back down to just below the cover of the F/E tank, but the trickle is nowhere near enough to form a siphon (and if I thought it was I would drill a hole in the top of the inverted U). The system has Sentinel inhibitor and 2 – 3 weeks ago I took a sample when emptying the Magnaclean for a bright wire nail test, and they’re still OK.
I’ve turned the pump down to minimum, maybe a little improvement, but it hasn’t stopped. The trickle starts immediately HW is called, doesn’t have to get hot first.
I’m baffled, as according to my calcs the headloss in 150mm pipe length is < 0.2m, even at 5m3/h, which is something like the pump output at maximum setting and zero head. And at say 2m3/h at minimum setting I get headloss 0.03m. So I would expect my 0.75 m to have stacks in hand even in worst case. Two boiler manuals I have both say minimum height of open vent loop 450mm above F/E tank water level.
Some pics attached. I don’t think anything outside the airing cupboard has any bearing on the case, but I can give more details – boiler model etc if necessary.
Has anybody had anything similar or can make any suggestions?
I have a conventional system, heat-only boiler, F/E tank, HW cylinder, diverter valve. Upgraded an earlier system in 1998, plumbed boiler - open vent (22mm) – cold fill (15mm) - pump. Open vent and cold fill are the recommended 150mm apart. Cold fill up-and-under. Both pipes go straight up to the F/E tank.
When I retired in 2010 I did some improvements including fitting a Magnaclean and changing the galvanised F/E tank for plastic. There was some sign of water coming out of the open vent, so I lengthened it to 750mm above the water in the F/E tank.
I’m fairly sure it was OK after that (no more water coming out of the vent).
Earlier this year the pump (Grundfos 15-50) was getting noisy, so I changed it for a Grundfos UPS 2. Everything seemed fine, but the other day I happened to feel the pipes and the open vent and cold fill were hot. There was a steady trickle of water from the open vent.
The vent outlet is brought back down to just below the cover of the F/E tank, but the trickle is nowhere near enough to form a siphon (and if I thought it was I would drill a hole in the top of the inverted U). The system has Sentinel inhibitor and 2 – 3 weeks ago I took a sample when emptying the Magnaclean for a bright wire nail test, and they’re still OK.
I’ve turned the pump down to minimum, maybe a little improvement, but it hasn’t stopped. The trickle starts immediately HW is called, doesn’t have to get hot first.
I’m baffled, as according to my calcs the headloss in 150mm pipe length is < 0.2m, even at 5m3/h, which is something like the pump output at maximum setting and zero head. And at say 2m3/h at minimum setting I get headloss 0.03m. So I would expect my 0.75 m to have stacks in hand even in worst case. Two boiler manuals I have both say minimum height of open vent loop 450mm above F/E tank water level.
Some pics attached. I don’t think anything outside the airing cupboard has any bearing on the case, but I can give more details – boiler model etc if necessary.
Has anybody had anything similar or can make any suggestions?
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