I have a Intertherm M1M furnace and when It kicks on the combustion blower runs for a long time before the furnace lights.The red status light occasionally blinks two times and according to the label it's saying the pressure switch is open but Im not sure.It will click and the ignitor will start glowing and then It will click again and the ignitor will go out.It will usually do this several times before lighting.It doesn't do this all the time but sometimes It will click and click trying to light for 10 to 15 minutes.

Check for a clear unobstructed tubing on the pressure switch with no cracks, check the fitting this tube attaches to be sure it is not restricted. Good luck, Mike

Check for a clear unobstructed tubing on the pressure switch with no cracks, check the fitting this tube attaches to be sure it is not restricted. Good luck, Mike
I checked hoses and fittings and everything looked good.