as in fully hot, not bearable. It’s one of these thermostatic cartridge single mixer for both shower and bath jobs. I have swapped the cartridge (I had a spare) and swapped over the non-return valves with each other and same result. I am beginning to think the cold water pipe is blocked! I had some debris come through yesterday that got lodged in the shower head, but once I cleaned it out I had this issue. The cartridge and the non-return valves have just been de-scaled as per bathstore recommendations (50/50 vinegar solution for 1-2hrs, then silicone grease the o-rings). Please help, I am a plumbing novice!silvershower2013-07-05 05:59:11