Main suspect are the hot water valves. Are both sides cold or only one side?
Next is the IHKA control panel, and finally the IHKA control module.
Check the water valves first. Remove the wire loom from the plug at the valves. If they do not have power, they must be fully open. You can also slightly hit them with a wooden piece, sometimes they get loose again. If they open when power is removed, you have to check if +12V is coming in the wire loom. If so, you have to go further pack to check the IHKA control panel potentiometer etc.
Have a look at this link under engine and click how to repair water valves and aux pump.
click here