Hello,
I have an open vented central heating system with an un-vented hot water cylinder.
It is laid out in standard S-plan with 2 zone valves, one for hot water, one for Central heating. Hot water is 15mm from the zone valve central heating is 22mm from the zone valve, but 15mm to each radiator, I assume that it Ts off the 22mm flow return near each rad (but I a havent raised any floor boards to find out)
Vent is 22mm and Cold feed is 15mm, both teed off between boiler and pump and within 150mm of each other.
There is a bypass valve for pump overrun. Boiler is a greenstar 40cdi
In my system the vent pipe only clears 150-200mm above the water level of the tank (at the top of the upsidedown u bend) However there is no room to increase this height to the recommended 450/500mm, it is also not possible to drop the tank to get the required height.
The issue I have is that when the central heating turns off there is a small amount of water discharged (~100ml) from the vent pipe into the f+e tank. I think this is either because of the momentum of the flowing water when the zone valve closes has to go somewhere so it goes up the vent pipe and over, or there is a build up of pressure until the bypass valve opens and this causes water to be pushed up the vent pipe.
I also have a feeling the cold feed may be partially blocked (slight sticking of a magnet), but the cold feed is not replaceable due to access problems (I might be able to feed plastic through it though). However I did flush the cold feed pipe with mains water and the flow rate was good, so I think the problem is mainly due to the lack of height of the vent pipe.
Interestingly this only happens with the c-h and not the hot water.
I'm not sure when the problem started but I noticed it due to orange water coming out of the overflow pipe, this didn't happen until a BG engineer came round to service the boiler and decided that the pump would be better at setting #3 instead of #1 because one of the radiators was cold (I have since bled the radiator and turned the pump down to #1). Other causes may have been having the h/w cylinder changed to an unvented (not BG) or when the boiler got changed before I bought the place (maybe to one with pump overrun).
I have seen this thread :
//www.diynot.com/diy/threads/ch-sytem-vent-pipe-diameter.158037/
And the problem seems similar, in the third diagram down there is a surge arrester which I think would do the job of absorbing the extra volume of water in the vent pipe without compromising its safety? However I can't see these for sale anywhere so I assume you have to make one?
The other solutions that may be possible are:
1) To route the vent pipe in a zig-zag (or coil) so it can accomodate a greater volume of water (in the normally air filled bit) before it goes over the top of the vent.
2) To join the feed and vent pipes together just under the tank and hope that this will provide and alternate path for the surge.
Any suggestions or help welcome?
I have an open vented central heating system with an un-vented hot water cylinder.
It is laid out in standard S-plan with 2 zone valves, one for hot water, one for Central heating. Hot water is 15mm from the zone valve central heating is 22mm from the zone valve, but 15mm to each radiator, I assume that it Ts off the 22mm flow return near each rad (but I a havent raised any floor boards to find out)
Vent is 22mm and Cold feed is 15mm, both teed off between boiler and pump and within 150mm of each other.
There is a bypass valve for pump overrun. Boiler is a greenstar 40cdi
In my system the vent pipe only clears 150-200mm above the water level of the tank (at the top of the upsidedown u bend) However there is no room to increase this height to the recommended 450/500mm, it is also not possible to drop the tank to get the required height.
The issue I have is that when the central heating turns off there is a small amount of water discharged (~100ml) from the vent pipe into the f+e tank. I think this is either because of the momentum of the flowing water when the zone valve closes has to go somewhere so it goes up the vent pipe and over, or there is a build up of pressure until the bypass valve opens and this causes water to be pushed up the vent pipe.
I also have a feeling the cold feed may be partially blocked (slight sticking of a magnet), but the cold feed is not replaceable due to access problems (I might be able to feed plastic through it though). However I did flush the cold feed pipe with mains water and the flow rate was good, so I think the problem is mainly due to the lack of height of the vent pipe.
Interestingly this only happens with the c-h and not the hot water.
I'm not sure when the problem started but I noticed it due to orange water coming out of the overflow pipe, this didn't happen until a BG engineer came round to service the boiler and decided that the pump would be better at setting #3 instead of #1 because one of the radiators was cold (I have since bled the radiator and turned the pump down to #1). Other causes may have been having the h/w cylinder changed to an unvented (not BG) or when the boiler got changed before I bought the place (maybe to one with pump overrun).
I have seen this thread :
//www.diynot.com/diy/threads/ch-sytem-vent-pipe-diameter.158037/
And the problem seems similar, in the third diagram down there is a surge arrester which I think would do the job of absorbing the extra volume of water in the vent pipe without compromising its safety? However I can't see these for sale anywhere so I assume you have to make one?
The other solutions that may be possible are:
1) To route the vent pipe in a zig-zag (or coil) so it can accomodate a greater volume of water (in the normally air filled bit) before it goes over the top of the vent.
2) To join the feed and vent pipes together just under the tank and hope that this will provide and alternate path for the surge.
Any suggestions or help welcome?