How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Phil Your Own Question
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
Type Your HVAC Question Here...
Phil is online now
A new question is answered every 9 seconds

I have a rheem classic 90 upflow. Will not ignite. Cycles

Customer Question

I have a rheem classic 90 upflow. Will not ignite. Cycles then shuts down . Fault code indicates ignition failure
JA: How long has this been going on? And how severe is the problem?
Customer: Hasn't run this season yet
JA: Do you plan on doing the work yourself?
Customer: Yes
JA: Anything else we should know to help you best?
Customer: Checked vent. And is clear pressure switches seem to work. Changed out control board
Submitted: 8 months ago.
Category: HVAC
Expert:  Rick replied 8 months ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of you situation.

I need the actual model number for your unit. It's on the rating tag which is usually inside the burner compartment.

Customer: replied 8 months ago.
Expert:  Rick replied 8 months ago.

About how old is this unit?

Customer: replied 8 months ago.
Not sure10-12 years
Expert:  Rick replied 8 months ago.

There is no ignition failure code on a 10 to 12 year old unit. What are the LED's doing? do you have HSI (hot surface ignition) or a sprak igniter?

Customer: replied 8 months ago.
Spark igniter. I get 1 blink which on th door unit says 1 hour lockout
Customer: replied 8 months ago.
New control board says 1 blink is ignition failure
Expert:  Rick replied 8 months ago.

Ok, does it generate an arc after the inducer fan gets going?

Customer: replied 8 months ago.
No. put new one in and still no spark
Expert:  Rick replied 8 months ago.

You have a new board and new igniter and no arc?!

Customer: replied 8 months ago.
Expert:  Phil replied 8 months ago.

Hello, if you can take an exceedingly well focused close up photo of the wiring diagram glued to the inside of the blower service panel and attach it here using the 'attach files' link to the left of your send button I will mark it up with trouble shooting instructions.

Customer: replied 8 months ago.
Let me know if this works
Expert:  Phil replied 8 months ago.

THat worked well, thanks, ***** ***** half an hour or so to mark it up for you

Customer: replied 8 months ago.
10-4 thanks
Expert:  Phil replied 8 months ago.

Hello again, while you are waiting, tell me please in gruesome detail exactly how you checked the two pressure switches... if you used jumpers those would need to be placed **after* the inducer fan was running for 2 to 5 seconds, not prior to the inducer fan running.

Customer: replied 8 months ago.
I checked first with ohm meter across each switch to make sure they would pull in. I then jumperd after the fan started running
Customer: replied 8 months ago.
I can here the gas valve click and verified 24v. The unit cycles the main blower comes on but never ignites. I pulled the igniter and let it hang so I would be able to see spark. But nothing happens.
Expert:  Phil replied 8 months ago.

Hello, turn off power to the unit and unplug then replug each of the gang connectors two or three times, inspect for loose or corroded pins... replug all connections to the printed circuit board...

Clean the spark ignition rod and its ground with plumbers sand cloth and re-gap if its the original to 3/16"

we can go from there

Customer: replied 8 months ago.
I'll update you tomorrow I've been at this for 14 hours and need to get some sleep
Expert:  Phil replied 8 months ago.

THat will work, I get in at 8 am west coast time and am in until 9 pm

Customer: replied 8 months ago.
Good morning. Did all you said. got ignition once after a few tries. now as soon as I hear igniter unit shuts down
Expert:  Phil replied 8 months ago.

Thanks, ***** ***** facts it looks like a bad pin connection in one of the gang connectors failing after a few minutes run time, not easy to diagnose, but lets work in that direction, If it were a component problem you would not have been able to get it to fire at all.

Examine each pin socket, use a needle to mash the sockets a bit tighter