I've recently (last month) had a new thermostatic mixer shower fitted - the manufacturer is Mayfair (product code SFL119). Its gravity fed, with hot water from the tank in the airing cupboard and cold from the cold water tank in the loft. Its been fine until today but today there is no hot water coming through it -putting the temp to cold, the cold comes through fine but move it to hotter and it slows to a tiny trickle - i.e. theres no hot water being allowed to come through. The water everywhere else in the house, including the bathroom where the shower is, is fine, both hot and cold - so the problem is isolated to the shower itself. As it's brand new it seems more unlikely to be a problem with the valve itself - I'm wondering if it could be an air lock? Would really appreciate any suggestions/ advice - many thanks!!