potterton boiler

[B & Z METALCRAFT]

i am about to change the pump on a central heating system which is heated by a large floor mounted potterton boiler. but there are four pipes on it 2 in

2out all 28mm.my problem is that i am only changing the pump that feeds the central heating to give it enough boost to get to the newly installed radiators in the loft ,but there are two pumps on the system so does one feed the hot water the other the cental heating?. i tried to work it out by switching off the lower pump and then switching the whole system on BUT the central heating came on ok and the pipes into the hot water tank got hot as well so now i don't know which one to change.also the control unit won't let just the central heating be on.

Any Ideas would be appreciated

thanks dave

[Michael Chare]

28mm is large enough for a gravity / natural circulation for the hot water tank.

Typical of a gravity system. In which often the room thermostat just controls the pump. The boiler uses it own internal thermostat to decide when to run (just keeps itself hot all the time it is on (but may be controlled in part by a HW Tank thermostat / HW zone valve.)

Does not explain the two pumps though. Could be that each of these supplies water/heat to different parts of the building. Maybe controlled by separate thermostats.

You need to follow the pipes to find out what is going on. (If practical IMHO)

Michael Chare

[BillV]

My god! thats an old boiler. I had one like that in my first new house in

1970...