Hi I have just fitted a new circulating pump and now the boiler only fires for a few mins.
I have made sure I have fitted it the right way followed venting procedures and bled the radiators.
The pump works but the hot water only seems to get to the 3 way valve then the boiler gives up. The position on the valve moves when switched between water and heating and it worked fine before pump replacement.
The logical explanation is you still have air trapped in the pipework which is preventing the flow. Either crack a joint open to let out water and the air plug, or consider popping the pump in backwards temporarily to shift it.
IT is well worth checking that you have fully opened the pump valves and not closed them.I.E that is open them in the same direction as you would a normal tap.I once had a plumber/gasman workmate of mine make the same simple mistake, took him ages to find the fault.