When the timer for our boiler (not combi) kicks in it blows it's fuse & all the house electronics blow. I replace the fuse then everything seems ok for a few days, till it blows again. Getting the boiler serviced next month but anybody ever had this problem ?
Make sure you only put in a 3 amp fuse othewise you will weld the timer contacts together. You obviously have an electrical fault possibly caused by water, could be the pump or a drip somewhere. Best to get it done ASAP otherwise you could be without heat.
Apart from the main power wiring (not very likely since it is only at timed "on" times that you have a problem), to me the most likely culprit would be a zone valve that has shorted out somehow. If you feel unable to trace the fault yourself, get someone else to do it for you. Tradesmen are a lottery, particularly in some parts of the country, so good luck.