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 Dan Linger Your Own Question
Dan Linger
Dan Linger, Lead Technician / Energy Consultant
Category: HVAC
Satisfied Customers: 62
Experience:  16 years of experience. Factory trained by American Standard, Bryant, Carrier, Rheem, Ruud & others
Type Your HVAC Question Here...
Dan Linger is online now
A new question is answered every 9 seconds

I have a Trane 90 percent efficient natural gas fired furnace.

Customer Question

I have a Trane 90 percent efficient natural gas fired furnace. Unit runs for a hour or two than the unit keeps going through fire off cycle. The inducer motor never shuts off and the H.S.I. has power but seems to short cycle never opening gas valve to sense flame. Checked all limits never see any open when goes through this cycle. It does this repeatdly and never goes into lockout and eventually will fire off. This short cyling between H.S.I. coming on and off varies when not working comes on and off every 5 to 10 seconds. When it does light off it goes through complete cycle leaving H.S.I on for 15 secs then opens gas valve and all is well for awhile. Please help I am thinking bad board but it has this relay wired to gas valve looks like a sequencer for electric furnace wired in series with gas valve. No wiring diagrahm extremely difficult to get to. model # XXXXX serial # XXXXX
Submitted: 6 years ago.
Category: HVAC
Expert:  Dan Linger replied 6 years ago.

The one thing I don't see in your diagnosis is voltage to the gas valve.


If the ignitor is glowing, the next step is for the board to send 24 volts to the gas valve. You should hear it click when it opens. If you get 24 volts at the gas valve and it does not open, you have a bad gas valve. If you do not get 24 volts at the gas valve, you have a bad control board.


Good luck.


Thanks, Dan

Related HVAC Questions