- Messages
- 18
Hi,
I'm coming to the brainy forum for a proper answer!
Scene - vented system, was originally gravity with Aga, then oil boiler with integral pump, then new oil boiler last year with fully pumped "Y" system.
I have problems with air in radiators.
I find there is a single 22mm expansion/fill pipe that comes off the upper primary to the cylinder. I expect this is OKish in the summer, even though it is after the pump, but in the winter when the cylinder is not calling for heat and the valve shuts it effectively means the expansion/fill pipe is only connected through the return via the cylinder and certainly could not vent any air, not a good idea.
I have looked at many forums, and seen some very silly comments by plumbers and DIY'ers (as I am -a DIYer, but I hope not too silly) that give opinions on single expansion / fill pipe or two pipes.
I read one comment that the expansion pipe will allow the expansion easier because it has less pressure in because there is a lot of water in the tank compared to that in the open vent pipe so the weight on the fill pipe is greater but surely the head of water will begin the same in both pipes and in effect the head will increase in the expansion pipe in an overflow condition?). I have seen that two pipes are necessary because if the boiler is overheating and the steam is going up the combined pipe how will the cold water also flow down it at the same time (surely if the system is under pressure from the overheating it would not be drawing cold water in from the fill pipe?).
I have read this on a plumber's site "Yes it is possible to have a combines feed & expansion, however, the central heating has to be designed specially, so that it can take a combined cold feed & open vent. Due to the extra cost involved, for this reason it makes more sense, to have a separate feed and expansion. " and on the same site "Why is there a service valve on the cold feed pipe? There are some emergency plumbers that don’t believe in fitting a service valve due to extra dangers, but is handy for any maintenance required." Hmm.
"
I was born an engineer - even if my career took me in another direction, so I crave reasons. I need to ask the experts here because I have found you give reasons and not just "do this", I value the wisdom here.
I intend to move the pipe to join the flow just before the pump. I will put a bleed screw or self bleeder on the old expansion pipe.
Space is limited so if I went for a single 22mm pipe I would only need to swap an elbow for a T for the new expansion / Fill pipe and add a couple of 45 degree elbows to join up with the old pipe.
I could just about cut the flow before the pump and squeeze in enough gap for a 15mm fill and 22mm expansion pipe if the new T joints are close together (less than 100mm).
Adding the 15mm pipe will mean some grovelling about in the fibre glass in the loft.
So, my authoritative friends - combined expansion/flow or two pipe?
I'm coming to the brainy forum for a proper answer!
Scene - vented system, was originally gravity with Aga, then oil boiler with integral pump, then new oil boiler last year with fully pumped "Y" system.
I have problems with air in radiators.
I find there is a single 22mm expansion/fill pipe that comes off the upper primary to the cylinder. I expect this is OKish in the summer, even though it is after the pump, but in the winter when the cylinder is not calling for heat and the valve shuts it effectively means the expansion/fill pipe is only connected through the return via the cylinder and certainly could not vent any air, not a good idea.
I have looked at many forums, and seen some very silly comments by plumbers and DIY'ers (as I am -a DIYer, but I hope not too silly) that give opinions on single expansion / fill pipe or two pipes.
I read one comment that the expansion pipe will allow the expansion easier because it has less pressure in because there is a lot of water in the tank compared to that in the open vent pipe so the weight on the fill pipe is greater but surely the head of water will begin the same in both pipes and in effect the head will increase in the expansion pipe in an overflow condition?). I have seen that two pipes are necessary because if the boiler is overheating and the steam is going up the combined pipe how will the cold water also flow down it at the same time (surely if the system is under pressure from the overheating it would not be drawing cold water in from the fill pipe?).
I have read this on a plumber's site "Yes it is possible to have a combines feed & expansion, however, the central heating has to be designed specially, so that it can take a combined cold feed & open vent. Due to the extra cost involved, for this reason it makes more sense, to have a separate feed and expansion. " and on the same site "Why is there a service valve on the cold feed pipe? There are some emergency plumbers that don’t believe in fitting a service valve due to extra dangers, but is handy for any maintenance required." Hmm.
"
I was born an engineer - even if my career took me in another direction, so I crave reasons. I need to ask the experts here because I have found you give reasons and not just "do this", I value the wisdom here.
I intend to move the pipe to join the flow just before the pump. I will put a bleed screw or self bleeder on the old expansion pipe.
Space is limited so if I went for a single 22mm pipe I would only need to swap an elbow for a T for the new expansion / Fill pipe and add a couple of 45 degree elbows to join up with the old pipe.
I could just about cut the flow before the pump and squeeze in enough gap for a 15mm fill and 22mm expansion pipe if the new T joints are close together (less than 100mm).
Adding the 15mm pipe will mean some grovelling about in the fibre glass in the loft.
So, my authoritative friends - combined expansion/flow or two pipe?
