My usual evening tv watching has just been interrupted by really loud clanging/banging noise in roof. Just about light enough outside so saw water spurting out of what looks like an overflow by the front door. Noise & water have stopped now & I've switched off the boiler as it had a red light & I'll be worrying about it all night.... Should I ring British Gas or find a local heating engineer first thing? Has something similar happened to anyone? Any advice welcome!