It's quite likely the main selector switch contacts are corroded.
Can you prevent the on-off-on-off by holding the selector switch in a certain position?
If so, turn off the boiler and importantly, mains power supply at the main isolator.
Remove 2 large screws at top of control panel - control panel will now swing down revealing circuitry etc.
Now also, remove the small screws which secure the metal trim plate of the control panel.
Pull off thermostat and control switch rotary knobs.
Trim panel will now be able to be removed.
This will reveal 2 large crosshead screws securing main selector switch - removing these will allow selector switch body to be removed from rear.
WRITE DOWN THE WIRE COLOURS!
Now remove the switch.
Ferroli replacement part number is:
3980123/0
(new replacements don't have the fixing threads older switches did - you probably need some suitable self tapper screws)
If it's an older switch you have, it will be an open skeleton design - these can be repaired effectively by liberally covering with a thick paste of salt and vinegar, working the mush into all the gaps, and operating the switch a load of times. Do this for 3 or 4 minutes, adding a few extra drops of vinegar from time to time. Then rinse THOROUGHLY for several minutes in clean water, and allow to dry overnight before refitting.
Salt and vinegar for some reason, dissolves copper-based corrosion like nothing else.
Other possibilities for failure would be one of the several thermostatic switches going bad. These are a push-fit onto various pipes and have 2 spade terminals. They can sometimes be 'jarred' back into action by several good hard bangs on a table after a spell in the freezer but should still be replaced ASAP if found suspect, since they are a safety feature.
Use this info entirely at your own risk.
passerby, September 2008
