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Lennox Furnace Intermittent Ignition Failures

PMR63
PMR63 Member Posts: 4
in THE MAIN WALL

Lennox Elite 96% efficient, two stage, natural gas furnace model #EL296UHV, 66,000 BTU having intermittent ignition failures. Furnace installed 11/2015 by previous owner. Have owned home for 2 years and had no issues. Just started this heating season in NE Illinois.

Furnace is communicating, but is wired in 24v mode and controlled by a Honeywell Prestige IAQ thermostat. Inducer starts with no issues, hot surface igniter glows, gas valve clicks and opens, burners ignite and within one second, furnace shuts down. This will continue until furnace goes into soft lock-out, if it does not successfully ignite. This seems to occur during the overnight hours. Temp drops from 70 to 66 at 10pm and variable speed blower runs in fan-on mode from 10pm to 7am to keep air moving. Work from home, so am down in lower level office by 5:30am and find furnace in soft lock-out. Turning off power switch, waiting for 30 second or so and then turning back on always results in successful ignition.

Tech was here yesterday and actually did testing of components - was impressed by his thoroughness - and found no identifiable issues. He tested gas pressure in both lo and hi fire and found them to be out of spec - too low on lo and too high on hi. He reset them to furnace specs. He also looked for venting blockages - there were none. Furnace ran all day and up to the 10pm set-back with no issues. Came down this morning at 5:30am and furnace was in soft lock-out. Turned power off and on and furnace ignited with no issue and has run since then.

Interested in thoughts around what might be causing this issue?? Checked all of the ground connections and all are tight. Don't want to start throwing $$ at parts without a clear diagnosis. Though it's not cold enough here to worry about freezing, I do travel for work and don't want to leave this unknown hanging out there. Thanks in advance for your expertise.

Comments

  • JUGHNE
    JUGHNE Member Posts: 11,259

    This has all the symptoms of a flame sensor that needs cleaning.

    However if you just had service that would/should have been done.

    Some furnaces have a combination flame sensor/glow ignitor. Not something you would try to clean as they are very fragile. Usually fail to glow correctly and get replaced.

    HVACNUT
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,157
    edited November 13

    Flame sensor is not sending the signal bacl to the ignition control.

    1. Clean flame sensor
    2. Check that you have a good ground path from flame to control so the current can get back to the control
    3. Replace flame sensor

    If those three repairs don't work, call a professional

    EDIT: After looking at your I/O manual, https://www.manualslib.com/download/990464/Lennox-El296uhv.html there is a separate flame sensor that can be cleaned.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • mattmia2
    mattmia2 Member Posts: 10,754

    That ground path and flame sense path back to the control is a long one, in addition to checking that everything from the burner back has a good electrical connection, make sure there isn't a chaffed or burned spot in the wire to the flame rod that is grounding somewhere.

  • PMR63
    PMR63 Member Posts: 4

    The tech that was here yesterday said he tested and cleaned the flame sensor and it checked out OK - not sure what that means in terms of specifics. If that's the case, could it still be the culprit? Since the reset early this morning, the furnace has run without incident throughout the day. Thanks.

  • SuperTech
    SuperTech Member Posts: 2,382
    edited November 13

    96% efficiency condensing furnace? I would be much more suspicious of an issue with the one of the pressure switches not closing when it's supposed to or opening when it's not supposed to. Could be a problem with the draft inducer or condensate drainage.

    Don't reset the power to the furnace until you verify what fault the fault code is indicating on the control board.

    mattmia2
  • mattmia2
    mattmia2 Member Posts: 10,754

    I would think the pressure switches woudl stop it before it got ot ignition unless one is flipping over on ignition for some reason, but like @SuperTech said, look at what code is flashing on the LEDs in the blower compartment, there is usually a little site glass in the blower door to see the lights.

  • HVACNUT
    HVACNUT Member Posts: 6,238
    https://forum.heatinghelp.com/discussion/comment/1819952#Comment_1819952

    If the tech has the meter to test it, yes.

  • PMR63
    PMR63 Member Posts: 4

    Was locked out again this morning. Here are the error codes from the control board:

    E271 - Soft lock-out - Exceeded maximum number of retries. Last retry failed due to pressure switch opening.

    E227 - Low pressure switch opened during trial for ignition or run mode.

    E229 - Ignition on high fire.

    Furnace is producing condensate and draining freely. Inducer revs up to speed immediately and there is no sloshing water noise. Power reset and started up on 1st try - as usual.

    Thanks.

  • HVACNUT
    HVACNUT Member Posts: 6,238
    edited November 15

    Pressure switch open could be a blocked flue.

    The ignition on high fire is weird. Is it redundancy? If Stage 1 fails, will it attempt Stage 2? I've never seen a code for that.

  • pedmec
    pedmec Member Posts: 1,026

    Check for obstruction were the pressure switch hose ties into the secondary heat exchanger collector plate. poke it out with a paper clip on the collector plate. sludge builds up in the bottom of the secondary heat exchanger and will cover the hole, even PVC shavings will cover it.

  • mattmia2
    mattmia2 Member Posts: 10,754
    https://forum.heatinghelp.com/discussion/comment/1820237#Comment_1820237

    what does the manual say that means? does it mean it tried high fire and ignition failed?

    maybe it only does it when it is trying for high fire

  • PMR63
    PMR63 Member Posts: 4

    Thank you for your helpful comments. I'll need to consult the furnace manual regarding the error codes. My experience has been that the furnace normally starts/fires in stage 1 and then ramps up to stage 2 if the thermostat is calling for stage 2 heat. The furnace sits in a walk-out lower level, so the intake and exhaust are high up on the back wall of the house. There's about 35 feet of 2" pvc vent pipe from the furnace outlet to the exterior. When I investigated above the ceiling tiles yesterday, I saw that the vent is barely sloped and toward the exterior, instead of the furnace. The pipe seemed heavy and probably contains condensate that is unable to drain. I am going to have the exhaust re-piped correctly. I will take a look at the pressure switch hose connection to the collector box to make sure it's clear. Thanks again.

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