By "purge blower" I presume you mean the blower
which blows air into the combustion chamber. What
happens when it "tries to fire"? Does the hot
surface ignitor glow, and the gas valve open?
So, you say that when you turn the thermostat up
hard and far, the furnace runs?
Of course, there are two fans. One to supply air
to the fire. And one to blow heat into the
building. Some of the more complicated furnace use
a timer, to turn on the blower fan that blows the
heat into the building. I can't comment on the
Lennox, never worked with that brand. Others use a
heat sensor, or other device to know when to turn
on the hot air blower.
A tech with Lennox experience would be more help.
Too much electronics.
Christopher A. Young
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