Need good 12V power.
Check the furnace 12V DC fuse is good.
When you set t-stat to 'heat' and then set temp (higher than actual) do you hear a click at t-stat?
Furnace fan should then come ON.......blows to purge combustion chamber of any unspent gas...then spark electrode 'fires' lighting main flame. Main flame is 'proven' via mili-volt signal thru spark electrode back to circuit board to keep gas valve open until temp set point is reached
Could be blown furnace fuse
Could be faulty t-stat
Could be tripped on/off circuit breaker switch (on furnace frame----allows 12V DC power on one side of timed delay relay so power can go to fan motor)
Could be faulty time delay relay (either a stand alone type of one that is part of circuit board)
Check DC fuses.
Pull cover off t-stat and twist furnace & power wire together...fan should come on, purge and furnace fire off.If so....replace t-stat
Doesn't work......
Then remove access cover.
Check ON/OFF Circuit breaker on frame....reset and try again.
Nothing.....
Pull connector plug on furnace circuit board. Push it on/pull it off couple times to make sure good contact.
What Brand/Model?
