Hi,This is risky business, not responsible for damages on your end. We *keep going until *you are happy. I come and go. be patient
It could be a weak flame sensor in the pilot light flame... use sand paper to clean that off real well.
If that fails, replace the switch. those are generally not expensive at all, remove it, mark how it is wired on a sheet of paper first.. then take it to a hardwares store for a match up.
Let me know if you need further elaboration, Phil
What does the sensor look like? Should I get an electrician to change out the switch? Is it safe to change by myself? Do I need to turn off a circuit breaker?
The sensor is either a 2" long thin rod with a spaghetti sized copper tube going to the gas valve and screwing into the gas valve... or a 2" long fatter tip, small finger size, connected to the gas valve by wires.
If you can give me the model number of the Lennox unit i can tell you if its safe for you to change... or you can find the switch in the main house panel that kills the Lennox when its running... then it would be safe for you to change the switch.
Look all that over and get back to me, Im in all day, Phil