No pressure indicated on gauge and yet Radiators appear to be heating ok. Switching on Hot water Tap brings on Flame light, but goes out. Hot water supplied briefly, after usual delay but then goes cold. Have tried to refill the system using the two Taps, but nothing happens. Have done this sucessfully in the past. That time, I could hear the water re-charging the system. Not aware of any leaks in system. Could this be a faulty Tap or a valve elsewhere in the heat exchanger circuit? Has anybody else out there experienced this fault? Any help on this matter would be greatly appreciated as this is for my Mother who is a poor pensioner...

DewTcalls, December 2007

It sounds like the hot water thermostat has an intermediate fault, if the system was low on water the fun wouldn't run and the boiler would not ignite at all. The problem with these boilers is a faulty gauge, if the system was over pressurising the auto refief valve would release and you would get water running out of the discharge pipe. the problem with the system not filling could be two reasons-1 low incoming pressure, this could also be the reason for no hot water 2- a blocked filling loop. You need to check the incoming pressure on the water main to diagnose if this is the problem. The auto bypass is there to enable the flow of water through the heating circuit if a blockage or a trv shuts down creating pressure greater than 3 bar within the circuit this in turn protects the pump and internal components. If the water pressure is ok it is probably the thermostat or a problem within the pcb, without more info i cant really diagnose.

DJHays, December 2007

Further developments to question above:
I have checked that water is flowing through inlet tap, One way valve and Tap connecting to Central heating return and found to be ok. The second Tap connects to the "Central heating return valve". Is this one way? If so, I assume the water passes through the Main heat exchanger then out of the CH flow service valve? What is the function of the "Automatic bypass valve" on the linking tube between CH Out and CH in?

DewTcalls, December 2007

Further developments to question above:
I have checked that water is flowing through inlet tap, One way valve and Tap connecting to Central heating return and found to be ok. The second Tap connects to the "Central heating return valve". Is this one way? If so, I assume the water passes through the Main heat exchanger then out of the CH flow service valve? What is the function of the "Automatic bypass valve" on the linking tube between CH Out and CH in?

DewTcalls, December 2007