haunting us to despair ?

I have a ravenheat rsf 84et,its been nothing but trouble since i had it fitted,It has a mind of its own, works when it wants to, fires up when no taps are running and no c/h on ?. I called out a boiler repair man, he replaced a valve and broke the pump while doing this, i replaced the pump. the man said he would come back the next day to finish the job but never did, cold bath or hot bath take your pick . its pot luck if it works or not when we get up. can someone tell me why this boiler is acting so strange ???