I have a potterton boiler, feeding the heating and hot water. The hot water is held in a vented cylinder and has no immersion element.

Hot water flows out from the pump at a high temperature. The pipes then disappear under the house and the only access I then have is at the water cylinder. The hot water by this time has cooled sufficiently for me to be able to hold my hand on the top pipe of the heat exchanger. The lower pipe in the heat exchanger is cold. The tank takes a day to heat up.

I think the air lock is under the house.

I have bled the pipe which runs on from the top of the heat exchanger top pipe, but get no escaping air.

Any suggestions.

Plumbed Out, February 2009

Diverter valve sounds a good possibility, then again most 3 port valves de-engergise to the HW position so logic would state that the heating would thus be the problem. however there are exceptions to the rule!!! try this..... make sure the rads are cold..... whack the Hot water ONLY on and wait for the system to warm up..... now feel the pipe as far from the diverter valve as possible (about 30cms should do) if its hot then the valve is sending the water down the CH circuit..... another possibility is crap in the coil causing restricted flow and poor hw performance.... start with this test though.... oh, and make sure if its a long run to the cylinder, the pipes are lagged....

dave, BG, February 2009

Hi Darren,

Thanks for the reply.

The central heating works fine. I have a motorised 3 way valve, which is fairly new and is working fine. I can select either hot water or heating, or both together, without any problems. The problem with the hot water pre-dates the new valve.

The hot water side of the system is very hot coming out from the pump, but cools significantly by the time it reaches the cylinder on the next floor.

Any other ideas?

Plumbed out, February 2009

hi

i am assusming that the central heating is working ok

it sounds like you have a system boiler, which uses the heat from the central heating to heat the water, it sounds like you might have a problem with the diverter valve/switch and one way to find out is switch the hot water on and see if it heats up the rads, as could be stuck open, if this works you will need to get a plumber in to repalce the part,

darren, February 2009