Furnace expert needed for strange ignitor issue

It all started with a continuous clicking noise and not running at all. I've replaced the control board, ignitor, gas(smart) valve, and now the pressure switch. Still the first cycle will sometimes start up and run for five minutes before the orange glow appears. Sometimes the pilot will not light and the orange glow from the rods will go away but the first cycle is still running. Sometimes the glow will come back and after a few more minutes the pilot will finally appear and the gas jets will fire up. Sometimes during the first cycle the orange rods come on and off a couple of times but then the first cycle will just shut off. But strangely it acts normally 95% of the time. Why this delay at times? Bad gas flow? Bad ignitor even though it's brand new?

 

Are you getting any codes from the control board?

Check and clean the opening in the nipple of your inducer motor (where the hose to the pressure switch attaches). It sounds like the pressure switch is not always switching or is dropping out. The inducer blower can have crud buildup partially blocking the nipple.

 

Thank you! I'll try that. Here's one for you... Last night the gas jets never turned on but the blower was running for five minutes or so and has done this a few times the party two days. Any ideas what that could be? It turned off as normal. Later it all turned on and ran correctly with all cycles kicking in as normal.

 

Are you talking about the main blower or the little draft inducer blower on the furnace ?

The pressure switch connects to the draft inducer with a small piece of rubber hose. This path MUST remain open and unclogged. If the pressure switch doesn't get the change of pressure, the igniter won't light and the startup process wont complete. Like Woody mentioned.... it's not uncommon for the inducer blower port to become blocked or partially clogged.

If you have a voltmeter you can connect it to the pressure switch and watch the 24vac thru the switch. If you read 24vac.... the pressure switch is open and not recognizing a pressure change.

 

The draft inducer comes on and the orange glow from the heat sensor will not always come on right away. Sometimes it comes on right away but other times it comes on after a couple of minutes but goes off again. Then it glows again for twenty seconds or so and may or may not light the pilot. Should the heat sensor be replaced or cleaned? Should the pilot assembly be replaced?

 

You should connect a meter to the pressure switch to make sure it's actually closing when it's supposed to. If you connect a meter and set it to AC volts..... you should measure 24vac on the two terminals before the inducer starts. Once the inducer starts you should measure 0 volts.