Central Heating Expansion Overflow

[alecv]

I have just had a new wall-mounted boiler (glowwrom micron 50ff) fitted and I interfaced the pipework to my existing system (having replaced a back boiler). I have fitted the cold feed and the expansion pipe in the flow, close together , before the pump. This then feeds a three-port valve, one output to Rads and the other to the Top Cylinder Circ pipe. This cylinder pipe originally had a 15 mm expansion pipe into the loft tank. I replaced this with 22mm and originally shared the top of the other expansion pipe into the loft. I joined it at approx 2 feet above the entry to the cylinder with a 22mm T. The system appears to work but there would now seem to be a link between the CH flow and the HW Circ. which does not seem right. So, I ran a separate expansion pipe into the loft cylinder. On switching on however, the cylinder overflow is running with water. Turning down my pump reduces the flow but does not stop it. As I need hot water and Heating I have temporarily returned the system to how it was but would appreciate any advice on how I should solve this. Alec

 

[etype]

Normally put - boiler - vent - feed(expansion pipe) - pump - bypass - motorised valve(s). Vent and feed within 150mm of each other. Don't normally need another vent, but do need an air bleed valve teed off primary flow near where it joins cylinder.

 

[oilman]

etype is right, get rid of the 2nd vent it has no purpose, and put a bleed point in instead. You could use an automatic air vent if you like.

 

[nickgray]

sorry to crash in but I have a bit of a related question relevant to this thread - what about sealed systems (e.g. combi boilers). can you rely on the system to push the air around enough and bleed it off at the radiators or the pump ?

 

[breezer]

mine you can (bleed air from rads) you should do this when sytem is off and cold then re fill as required

 

[oilman]

.......what about sealed systems (e.g. combi boilers). can you rely on the system to push the air around........

This is why the expansion vessel has the air pressure set just above the static pressure of the system. The air pressure must be set with the system pressure at zero, and should be checked every time the boiler is serviced. (BSS 7074 part 1)

 

[alecv]

Many thanks for your help. I suspected that this was the case and was intending to try and fit an air bleed valve next.

Alec