Bosch SGS5358GB/17 H2 error

Good morning all. I have come to this forum in the hope that you can help. The problem is as in the subject. So far I have resoldered a burnt joint on the heater relay on the control board and tested the relay. It clicks with 12v applied and the contacts close with zero resistance.I have also cleaned out the plastic water fill ‘maze’ on the left of the machine, there was some crud blocking the valve. This now clear.
The machine will run correctly on a low temp wash ‘quick wash’ but when a longer or higher temp wash is selected the display shows 2H (capital H) the machine will run with the error present and the water does get hot, but it doesn’t count down.
The only thing I can think that may be faulty is the control board. Anyone any ideas?

Malcolm