Have a ariston eurocombi sx20mffice boiler and when i switch on the heating or hot water tap the pump runs but wont ignite, if i close any one of the heating supply valves it ignites but will overheat very quickly, do i have a blockage in system or pressure problems?
Can be a blocked pipe/heat exchanger but usually, in my vast experience of 3, doing it, it's a slow running pump. I've got some of them if you want one.
Now wait for everyone else to say it's something different .
If the pressure is OK and the auto air vent is OK and the differential water flow switch is OK (and the microswitch and the pipes to it) and the pump is OK it can be a slightly clogged washer on the front connection of the main heat exchanger. or it could be something else.
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