We have a pool heater that came with the house. We have never used or tested it since I moved here in Dec 2018. Today I try to switch it on and nothing happens. The display is blank. I checked the breaker, switch on the heater and gas valve. everything is on. There is no separate breaker for the Pool heater. Only one for Pool. (probably controls the pump/filter/Heater). What can I do to troubleshoot? See the attache dpics