My RHFE-551FA Rinnai heater cuts out for no reason. On his first visit a heating technician cleaned it and checked all the specs which didn't help. On the second visit he ran through all the checks suggested by Rinnai tech service and that didn't help either. For another model, Therinnaeguy suggested checking the small harness from the main board to the sparker board (which the tech did) and if the problem continued to replace the wire harness. Failing success with that procedure he recommended replacing the sparker board.

Would this work for my heater? What would a harness and sparker board be worth and where would I locate them? Thanks for any suggestions