Hello, I'd appreciate any advice on what to do.
My LX400 won't stay lit - I'm starting up the pool for summer - it lights and then after the blower comes on it runs 30 seconds or so and shuts down with an Air Flow Error on the control panel. The blower runs fine, and the air flow switch tube looks good - so I replaced the airflow sensor. With the new sensor, the heater fails almost immediately after the blower starts up prior to the ignitor coming on - the ignition module flashes once indicating air flow fault. Huh? If I put the old air flow sensor back in, it purges, pre-heats, lights, blower runs, and it then stops and shows the air flow sensor fault on the control panel, not the ignition control. This is repeatable.
I looked at the sensors and they both look the same. I tried cycling the heater looking with an ohmmeter across the NO contact to Common, but I don't see the switch operating when the blower runs. I would have thought that the switch would close during purge, so that the controller sees it and knows it is capable of closing - if it doesn't it should fault right away. It then should open when the blower turns off for the preheat and ignition, then close again when the blower comes on after lighting. If it doesn't see it close it would shut down and show the fault. No?
In any case, I'm stuck. Maybe I have two bad sensors, but I would think they are so simple they would fail the same way. I'm assuming the system is working correctly since the blower runs fine and sounds like it always did. Do you think there is something in the flue? That is hard for me to get to so I haven't checked yet. Any other ideas or tips?
Thanks so much!