I recently bought a house that has a Hayward H400 IDPL2 LP gas heater. The problem I need troubleshooting is that the heater fires up fine, the display shows the current temp., no error codes but I can't increase, decrease or change modes. Basically, the control buttons are inop. At first I thought I'd order a new keypad but before doing so decided to dig in a little deeper. I remove the keypad, cleaned carefully and inspected the wiring ribbon. Looks good. The buttons aren't weather baked and when pushed they feel crisp like the contacts are working. I then remove the display board from the back of the keypad and inspected for fryed lookin areas, looks good. The main control board looks good and all the wiring checks out.
So the big question I have is, do I replace the keypad ($185), or the display board ($200) or the main control board ($165) first to see if that fixes the problem. I hate the 'spend till it's fixed' method so any help or advise would be greatly appreciated.