The shower in my master bathroom is no longer staying hot. It's hot enough for me if the knob is all the way over to the hot side, but not hot enough for my wife. I used to set the handle to more or less the center, so something has changed. The downstairs shower and all the rest of the faucets are fine so I don't think it's the boiler (domestic coil).
I've replaced the cartridge in the Moen mixing/diverter valve (the Moen site said either a 1220 or 1225 - I used a 1225) but the problem remains. I've been told that a hot-cold transfer is possible at any faucet so I've tried shutting off the supply to them; nope. I would have thought this would affect all faucets anyway. Any ideas?