That was my thought too (also what else did the diode damage when it blew)! The answer is I've no idea, could even be a fault somewhere else - not on the control board. Unless there are other suggestions, I could either replace just the diode, or try to replace all the components, then try again. However, there's no marking on RS1 or CR1, and I haven't been able to source any of the 3 relays manufactured by NAIS. These are DS2Y-S-DC12V-H271 and DK1a1b-12V AW3033 (2 of these). If I can't identify/get these components, I really have only one option before getting the board repaired/replaced. If someone is able to have a look at an identical board, that would be a great help!