20 Most Recent Grohe Grohmix Thermostat Valve & Trim - 34436 Questions & Answers

The problem might be fixed by removing the cartridge and cleaning it thourghly and resetting temp stop.Yes the cartridge could be bad but new parts are readily available. Depending on water quality conditions in you area it may be difficult to disassemble so it may be a good idea to have a plumber do it for you. Thank you.

your answer should totally be in the instructions of the valve that should have come with the valve,..good luck

Under the handle face is a gear stop. Look at it I think it needs to be rotated counter clockwise a tooth or two.