i might be inclined to give that a C3. my reasoning there is that a fault on the bouiler is more likely to trip the 6A MCB rather than the 3A fuse. ( i.e. no discrimination). tin hat fixed in place.I think we have come to the conclusion it is not a C2. How big is this house that you envisage it will be at the other end of? As has been said, we are talking about a boiler, on it's own circuit, in 1mm protected by a 6A OCPD and then a 3A fuse. How can it be dangerous (C2)?