Hi I have a Grohetherm Wireless 36022 Shower unit. I am not getting any hot water out of the shower although there is hotwater to all other taps. The unit turns on and flashes as normal but never gets to the default temp of 38degrees infact the water temp doesnt change at all from ice cold. The remote displays LIMIT and 38 degress keeps flashing. The main controller is located in the loft approximatly 2.5m from the hotwater tank. the hotwater pipe feeding the unit seems to cool down about a meter up from the tank. I have reset the unit and powered it off and back on. Any ideas?

it probably has an anti-scald control in the shower line that lets cold water in to prevent burns
If so that unit has a wax bulb that sometimes fails and the default fail setting is cool water
have a plumber check it out

hot water problem

shower head may need cleaned

Limit message is when the output water set temperature can not be reached, this is normally when the incoming hot water to the shower unit is not sufficiently hot. Service code 20 is something else inside the unit that is faulty, it could be a number of faults. Try reset Power down unit and re-start, it will either say Wait or Priming, after that it should restart, hopefully it will work. If not, you could have a internal fault with: The mixer valve/motor, the flow control valve or motor, the flow sensor. If you have hot water from other taps, then the mixer valve/motor is the most likely fault. If you only have cold water only from the shower head with limit message it could be the Hot solenoid controlled valve is faulty. Good luck as there are no spares available!

yes

You don't change the setting on the faucet or behind the shower wall. You change the mix in the hot water heater itself. New hot water heaters are set at a relatively lower hot-water-setting for liability purposes. To achieve a hotter mix, take the cover plate off the hot water heater. You will see a dial setting that allows you to turn up the heat. Depending on what type of water heater you have, there might be two cover plates (lower and upper). If so, you'll need to adjust both of these.

it is possible that the hot mix valve needs to be adjusted higher or there is a crossed plumbing line somewhere down the line. ( just wondering(?) are you tapped off a standard hotwater tank or a hotwater on demand system ? ). also, how is the hot water throughout the rest of the house ?

c...

make sure the rest of the house is getting good hot water to rule out a problem with your hotwater heater, if all other is ok then your shower valve may be clogged with trash on the hot side restricting flow and hot water. If its an ant scald shower valve you may need to raise the temp control.

yes it could be have you cleaned the shower head with clr it might help or you hot pipes might be blocked

Sounds like the pipe going to the shower head is vibrating. Not secured tightly indige the wall. That is about the only thing it could be in my opinion. Hope this helps you out .
Kurt