I have about 8yr old raypak 266 lp heater for spa/ pool and for the past year intermittently I would get ilo ignition lockout errors. Typically next day would operate fine. I removed control board and cleaned and checked all connections and worked pretty well for a while. I was / do think it's a control board problem but never could throw. $300 part at it and it had been working the couple times I used spa. Last night I got a different error when tries to light. When I get call for heat I get vnt and fll error. It does s park or light pilot . Is there vent switch I can measure with dmm?