which part of the board would you suspect, is it the main control board under the grey panel which drops down or the one which has the majority of sensors attached to it located nearer the bottom of the unit.
i have some experience a test meter and a soldering iron.
oddly enough the power is getting through to the immersion element which has two out of five element sections with power going to them.
Even with the compressor running and the power to the immersion elements the temperature still wont rise above 38c
heat exchanger section seems ok, 19c in 1c out. I will check the boards tomorrow as the system isn't in our own house. its in our holiday let which is down the track from us. dont think anything is damaged from a power surge as it all seems to operate as it should except this limiting of water temp. makes me wonder where the energy from the immersor and heat exchanger are going?