it may well be the blending valve. easy to tell, just see if one of the pipes to it actually gets hot when the tap is running. What thermal store is it? if its one of the albion ones they scale up badly as the hot water coil is only narrow bore. The gedhills seem to last longer...a bit
I'd recommend replacing it with either a highflow combi or seperate boiler and UV cylinder depending on usage and water flow/pressure available.
Thanks for the reply mickyg, I checked the blending valve, both sides are hot but as soon as I turn the hot water tap on, the pipework on the lower side which I imagine is the outgoing to the taps goes stone cold almost instantly??
