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Loch KHB155 (new, 5mths) fluttery ignition with intermittent error

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wcs5050
wcs5050 Member Posts: 165
in THE MAIN WALL

Up to 5 logged errors per day now, but with automatic reset for success. Building heat and DHW so far unaffected by the lag.

This is from day one. Exhaust length is good, within the rules; gas pressure good. Just ran combustion and the numbers are within spec, but gas valve not responding to minor adjustments.

Will attach video.

Comments

  • HVACNUT
    HVACNUT Member Posts: 7,207

    Curious why the contractor wasn't called back on day one, 5 months ago. Where is combustion air taken? What is the pressure drop at the gas valve during trial for ignition? What are the combustion numbers that are within spec? Did you do high and low fire tests? Flapper on the Venturi is free?

  • hot_rod
    hot_rod Member Posts: 26,557

    On occasion they need to have the adjustment settings taken a bit out of range. A tech support person on the phone can help with that.

    It needs to be metered up when you call. Gas pressure and combustion analyzer connected and reading.

    Assuming it has adequate gas line size and pressure, it sounds like a burner adjustment is required.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • wcs5050
    wcs5050 Member Posts: 165

    I don’t know of any homeowners that use a combustion analyzer, or talk about adjusting the gas valve throttle. This is not an obvious hard fail problem. I’m surmising it was a day 1 problem shortly after I fired it off.
    New 3” centrotherm exhaust run over 30’ to roof terminal, air intake on 4” pvc over 8’ from open gable vented attic.
    High fire showing 8.8% CO2 on a 8-10.5% spec window, 5% O2 on a 2.1-6.6% spec window. Loch doesnt have low fire spec on this machine. Gas valve adjustment not showing to affect combustion.
    I can hear the flapper opening closing… Will check that. No manometer reading yet.
    Thanks all for considering.

  • hot_rod
    hot_rod Member Posts: 26,557

    Does it have a gas flex on the gas line? If so check pressure at the gas valve when at high and low fire.

    Some boilers light off at high fire and ramp down to modulate, so you need adequate pressure at light-off.

    Remove the air intake at the boiler and partially cover that opening to see if it eliminates the flutter. Another indication of more adjustment required.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • wcs5050
    wcs5050 Member Posts: 165

    Thanks HR! I forgot about that air constriction tactic. No flex on the fuel connection, all BMI. This one def lights on high and immediately drops to 10% rate. Thinking about it now I’ve had a few older HTP Elites where the gas valve was spoiled and could not be adjusted but would ignite well with constricted air flow.

  • wcs5050
    wcs5050 Member Posts: 165

    No effect to ignition with partial air intake constriction. Gas valve appears unable to be tuned, going in 1/8” increments on the throttle crests no change to exhaust component levels. Suspect defective gas valve.

  • wcs5050
    wcs5050 Member Posts: 165

    Sorry scratch that. Constricting air intake by 75% of 2” pvc open end coverage allows smooth ignition.

  • mattmia2
    mattmia2 Member Posts: 15,485

    what's the pressure? if it is already wide open ad there isn't enough gas, it can't let in more gas.

  • HomerJSmith
    HomerJSmith Member Posts: 2,704

    I never seem to get enough information.

    What error code?

    What is the static and dynamic gas pressures to the gas valve?

    What make of combustion meter did you use and what were the readings at high and low fire? Recently calibrated? You didn't adjust the gas valve throttle by mistake rather than the screw?

    Are the gasket connections secure and tight from the gas valve to the blower to the combustion chamber?

    Are all the tubing securely connected to the gas valve?

    You did unplug the gas valve wiring and re-plug, also, the wiring on the connection board and main board?

    GGross
  • mattmia2
    mattmia2 Member Posts: 15,485

    air leaks won't affect the mixture, they will just either cause a gas leak or underfired depending on where they are

  • HomerJSmith
    HomerJSmith Member Posts: 2,704

    If the gas orfice nut is loose or the o-ring between the gas valve and blower is loose, air can be sucked into the gas mixture reducing the air gas ratio.

    wcs5050
  • wcs5050
    wcs5050 Member Posts: 165

    No failed ignitions logged after dial in of co2 on high and low fire… decent ignition behavior at that time, but messy and oscillating significantly 2 days after. Local man rep has me looking at Venturi assembly. Still no failed ignitions at the moment prior to Venturi replacement.

  • rick in Alaska
    rick in Alaska Member Posts: 1,513

    I would for sure get tech support on the phone, as some of these units fire better on the extreme of the range settings. Can't remember higher or lower. Also, on some of the KHN units, the air line fitting that the rubber pressure hose hooks on to have too small of a drilled hole, and can cause some issues, Unfortunately, it has been too long for me to remember, but you might ask about that.

    Rick

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