Potterton - Suprima 80 problem

I have one of the above which is about 8 years old, in the main it has been a good boiler.
About a year ago we had a storm with horizontal rain, some of which got into the balanced flue and stopped the boiler working. Our plumber came round, sucked out the pressure tube, and all seemed ok.
Since then, however, the boiler sometimes switches off for no apparent reason, it restarts ok by pressing reset.
Our plumber has changed the overheat thermostat, the temperature sensor and the electrode, but to no avail.
This failure may happen only once a fortnight or three times a day. Although it does not sound like a major problem, I am often away from home for prolonged periods, and am afraid it will switch off and the pipes freeze.
I don't think my plumber has any ideas as to the cause, have any of you encountered anything similar?
Thanks

Cue scorn of your man from those on high horses who will tell you you should have gone to a Boiler Engineer!

The Suprima is well known for this fault, which is due to the PCB. They've redesigned it, and it's a lot better, but it isn't cheap. It comes with replacements for all the unreliable connections and cables as well.

check out BBC WATCHDOG potterton suprima you will get a surprise pott now do a fixed fee repair

Before changing the said PCB it is worth looking at what ignition lead you have to the new spark electrode that was fitted.....

These come in two forms.....old type....material internals and red outer sheeth.....new type wire inside plastic outer clear/white outside.....

if you have old type then stick on a new one for about 2 quid....

worth a shot before spending £200 on new PCB.