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Lochenvar WHB110N (LP) doesn’t want to fire reliably (FLAME FAIL IGN)

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ElectricalWeenie
ElectricalWeenie Member Posts: 3
edited January 14 in Gas Heating

I’m stumped. The TL;DR is the thing ran for ten months just fine, now its under fired and doesn’t want to start reliably.

Here’s the long version: The boiler in question was hung on the wall in 2019 for a remodel and the project went dormant during Covid, never finished or fired. 

Fast forward to Feb 2025, the gas company failed to bring NG to the street so it was It was converted to LP with the mfg’s kit, a new venturi and blocking plate. A 1000 gallon LP tank was buried and the boiler supplied with 1” Tracpipe, about 20 ft downstream of the second regulator. Intake and exhaust are approximately 10 feet of 2” pvc with several 90’s in each, all okay according to Lochenvar.

Unit was commissioned, gas pressure was 12” wc at high fire and combustion was within limits (don’t remember exact numbers but were as expected). Unit has been running successfully for ten months. Tank got down to about 200-250 gallons and the unit started throwing FLAME FAIL IGN faults about every other attempt to fire. It would recover and run okay for a day and then start failing again. 

Tank was filled to 800 gallons but problem persists.

At high fire, Co2 is low at about 9.8% , O2 is 6.0%. Targets are 10.8 and 4.5. Gas pressure is good at 12”, in both idle and high fire. Gas value mixture screw has no effect on firing with a short, all blue flame.

Gas valve was replaced to little/no effect, actually the problem is a bit worse as start is even less reliable. Heat exchanger interior is soot/combustion particulate free, burner screen also clean. Igniter and sensor were cleaned, the very light buildup on them was whitish-grey.

I have checked for intake/exhaust blockages with an endoscope, I don’t see anything in the lines. I would check the delta-p across the heat exchanger but I have no idea of what it should be so I’m stumped and open to suggestions to troubleshoot further- and of course will answer any questions.

Comments

  • mattmia2
    mattmia2 Member Posts: 15,838

    water in the propane tank? regulator vent icing? did you check the pressure at the appliance when it happens?

  • pedmec
    pedmec Member Posts: 1,260

    Your combustion numbers are indicating that your running lean. Lochinvar chart indicates it wants anywhere between 10.5 to 11.5 on the CO2 on high fire. Increase the gas

  • ElectricalWeenie
    ElectricalWeenie Member Posts: 3

    Yes, gas pressure checks okay with both analog and digital gauges, both idle and running at the gas valve test port.

    Outdoor high pressure regulator is under cover, no icing. Indoor regulator feeding a manifold looks okay as well, pressure at 12” w/c with no discernible changes with other appliances running (range, fireplace).

  • mattmia2
    mattmia2 Member Posts: 15,838

    does the pressure test ok when it is having a problem?

    water in the propane will be harder to test for.

  • pedmec
    pedmec Member Posts: 1,260

    You dont need more gas incoming to the gas valve. You need to increase the fuel/air ratio in the burner. This requires a combustion analyzer. You need to increase your CO2 which in turn will lower your O2 to the proper value

  • mattmia2
    mattmia2 Member Posts: 15,838

    i thought they said somewhere in there that adjusting the valve settings wasn't changing the combustion but re-reading i'm not seeing that.

  • HomerJSmith
    HomerJSmith Member Posts: 2,736
    edited 12:02AM

    I guess that you used the proper conversion kit for LP conversion for your boiler. A common mistake in converting is the placement of the brass orifice in the tube coming from the gas valve to the fan. It is directional and I have seen it installed backward. The orifice has a number stamped on it an must match your boiler. It should have been checked with the instructions that came with the conversion kit.

    image.png

    Also, the baffle plate under the fan must be installed correctly.

  • ElectricalWeenie
    ElectricalWeenie Member Posts: 3

    Homer, my conversion kit did not have the brass insert nor did the instruction kit show it.

    The boiler and LP kit were purchased in 2019, perhaps they changed things since this was purchased. I do know the LP Venturi flapper diameter is different from the NG part, that was the only difference I saw. With respect to the baffle plate, it was installed

    aligned along the long opening edge. I honestly don’t remember but I don’t think you can rotate it 90 degrees, making a very small opening. It cut the area about in half from what I remember.

    Please note the unit ran successfully for ten months with the proper combustion readings. Now it’s quite lean and adjusting the gas valve mixture screw has no effect on the combustion analyzer, photo attached of the current condition. Installing a new gas valve did nothing.


    The only thing I can think of at this point is that there is a blockage in the heat exchanger that is reducing airflow thereby reducing gas flow. Am I barking up the wrong tree on that one? If not, how would I check that? Couldn’t I measure the delta-p across the hx? I know there is differential pressure switch that monitors for excessive pressure drop but that’s never thrown a fault.

    One thing stuck in my brain was my distributor sales guy mentioned that “you never want to run these things low on LP as they’ll soot up the heat exchanger and you’ll be replacing the most expensive part in the unit”. I expect that has biased my troubleshooting but I’m up a tree looking for wood at this point.

    IMG_0256.jpeg

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