Hi to community - I have a SR400LP, ~ 10 yrs old, in pretty good condition, looks good inside. Turn on the pump, then the heater; the fan spins up, but sounds different. I would say it has a warrbling sound. The Service Heater light is on on front of the panel. The heater burner will not lite.
Opened the heater and checked the back of the display board; AFS - Red, LED11 - Red, LED9 - Green. Opening the Control Box cover the Fault Indicator Light is flashing one time - Air Flow Switch.
I placed a jumper across the air flow switch connection - Service Heater light went out and unit fired up. But the initial fire up was not the usual whoosh and the low rumble from the burner. The exhaust air flow did not seem as strong as usual but I can not be sure since I never really took notice of the exhaust in the past. Verified blower inlet is clear, motor turns, sensing tubes intact, they are soft and pliable and in place.
To me, by-passing the AFS did not tell me if I have a bad switch , a weak blower motor that can't trip the AFS, both or something else. Am I at the point to start replacing parts? AFS first, then motor next?