As said by a couple of observant peeps on here this boiler is an m3080 original icos and is probably seven years old!!
(lasted this long FFS) Hope this satisfies you lot
But it will be an external fault of air, pump, or circulation probs but get someone to check as it could cause irreprable(sp) damage to boiler also get it checked and serviced including sump cleaned electrodes checke insulation panels condense checked etc if not yo could be in for more trouble
The house is only around 4 years old! I'm renting, so i'll get the agents to get it looked at asap. Thanks very much for all your opinions, now i know it's something i can't fix - i'll get a professional in.