Hi There,

3 or 4 weeks ago my trusty 12 year old Prima 80F boiler stopped working. At
the time I gave it a (small well calibrated) thump. It started working
again and I thought no more of it.

Today it failed again. In the specific failure mode:

....The controls are calling for heat.
....The pump is running and the fan is on.
....The pilot light is lit
....but no main burner.

I took off the bottom cover and can see the gas valve is connected to the
electrical control PCB/gubbins by a 4 way MOLEX style connector.

* If I carefully wiggle this connector the main burner lights straight
away.
* If I turn down the temperature control it turns off the main burner as
you would expect.
* When I turn up the temperature the boiler *sometimes* returns to the
failure mode.

I sense a dodgy connection or a dry joint.

Q. Is this a common failure mode?
Is there a specific connector or component that is the most common
source of this problem.
The benefit of your experience is appreciated!

David