On Wed, 3 Feb 2021 09:07:21 -0800 (PST), Dean Hoffman
wrote:

On Wednesday, February 3, 2021 at 10:44:39 AM UTC-6, trader_4 wrote:
On Wednesday, February 3, 2021 at 11:01:12 AM UTC-5, Jeff Gramza wrote:
Furnace is around 20 years old. Sometimes the main burners light and sometimes they don't. When they don't, I go downstairs, turn the blower motor off and flip the black switch to 'off' on the little beige box (smart valve?). Wait 30 seconds, reverse the process and the main burners come on. They may come on the next few times but when it starts to get cold in the house, I go downstairs and see the main burners haven't fired up. Doesn't appear the plastic hoses are clogged. Any suggestions where to start looking?
Are you sure they are not lighting or are they lighting, then going out? If it;s
the latter, could be a bad flame sensor. If it won't light at all, what is the lighting
method? Pilot light? Hot surface igniter? Is it high efficiency with a blower for
combustion? Could be a pressure switch, blocked vent to the outside.
It seems odd that the blower motor is actually running. (figure of speech?) The motors on the few furnaces I've had were started by some sort of heat sensor. So maybe the burners light, the motor starts, and.............................?
I suspect your problem is the same as on the neighbor's Tempstar -
the hose from the inducer motor gets condensation in it and eventually
the port itfice in the blower housing restricts to the point the
vacuum/pressure switches don't get the proper signal any more. Try
blowing through the hoses that connect to the inducer blower- if you
can't blow into the blower you will need to ream out the fitting -
sometimes a paper clip will do it - sometimes you need a drill.