My ideal minimiser se condensing boiler stalls several times after coming on in the mornings (burner light off but the fan keeps running) before staying on any length of time, it also bangs very loudly sometimes before stalling. 3 engineers have looked at this under the insurance and so far have cleaned the flue thoroughly, replaced the probes and the gas valve which made no difference. The last engineer figured out that the boiler runs perfectly with the cover off, which I tested over a weekend and confirmed the same. So must be something to do with gas/air mix? They are now out of ideas and I am concerned the insurance will say it is beyond ecomomical repair. Anyone have any ideas.