Please turn your furnace off.
Wait one minute.
Then turn it back on.
After that watch the furnace start up.
You will need to remove one of the panels to observe the following.
Gas furnaces have a start sequence they must go through.
The first step is that the furnace will get the signal from the thermostat
to turn on.
Then the induced draft fan will come on. Not all systems have this fan.
After that, if you have an induced draft fan, the pressure switch will close because of the induced draft fan running.
Once that happens your ignition will attempt to ignite the flame.
If you have a spark ignition the ignitor will spark. If you have a hot surface ignitor, the ignitor will glow very bright from being so hot.
This is when the gas valve should open.
The gas will not ignite.
Then the flame sensor will sense the flame.
Once the flame is sensed, the heat exchanger
will warm up.
After the heat exchanger warms up the indoor blower motor will start.
Please let me know how your system runs compared to the above description.