Grohe shower mixer, water always warm, never hot, even when turning temp up ?

Be sure this hot water problem is just the shower.

Check that cold water supply is on

Ive written a solution twice but for some reason it wont let me post it.I will try to abbreviate it.

You dont say how much flow it has when the pump isnt running but I suspect there isnt enough to turn on the sensor unless all the flow is one side. ie all cold.

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!

valve should have a gear like deal under handle that may need to be adjusted

The thermostatic mixing spool cartridge may be worn out. The low water pressure may indicate sediment in the cartridge as well. This can be easily removed by hand tools

The thermostatic stop is set too low. Havent set a grohe before but most other thermostatic shower valves work similar. pull off the handle(however a grohe handle comes off . . ) there should be a notched ring or stop which keeps the handle from going all the way hot. pull out the ring and turn it a few teeth hotter put back and reinstall handle try water temp and adjust again if necessary.

Do you mean the other faucets in the house are hot and only the shower is warm? If so there is an anti-scald adjustment on the faucet that needs to be turned up a few notches. Havent adjusted a Grohe faucet but most faucets you rmove the handle and behind the handle is a nothced adjustment ring that prevents the faucet from getting too hot. This ring, or stop, is pulled out and twisted clockwise(or counter clockwise to set higher or lower max temp, then pushed back. maybe you can look up grohe to see which way ring or stop adjusts for hotter water.

you need to change the cartridge, it is a temp control and is going bad so it keeps you from burning yourself it is like a mixing valve and is givng more cold water, that way you don;t get burned,,

There is a handle limit stop under the handle. Remove the handle with an allen wrench and you should see a plastic piece with a tab on it fit into the assembly. Remove it and rotate it slightly to allow more travel in the handle and reinsert. You will have to test it to see if it allows enough hot water to mix in. If it is still not warm enough repeat as needed. Once you have the water at a comfortable temperature reinstall the handle and enjoy.