Lochinvar WHN199 getting flame ignition fail regularly - only when propane tank was filled full
Hi! I've been struggling with this problem for a year or so.
I have a Lochinvar WHN199 that is giving a flame lockout error. It tries to light four times and goes into lockout. It is converted to propane, and only happens when the propane tank has been recently filled full, and starts working properly after the tank has been used for a week or so. The inlet propane pressure seems fine; 12.4". I tried replacing the gas valve assembly, but the problem still persists.
The boiler will light immediately if I remove the clear air hose attached to the gas valve assembly and lightly blow into it as the ignition is sparking. specifically, I can disconnect the hose at the three way split (see photo below), and lightly blow into it towards the gas valve. When it is in pre-purge, I don't feel any air coming out of the white air inlet pipe, but it is clear (no obstructions).
Any ideas?
Comments
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Have you checked the LP line pressure right after the tank is filled and before any appliances are used?
It seems that as you use the tank you may be dropping the pressure.
Is there a high gas pressure switch on the boiler?
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Have you checked the LP line pressure right after the tank is filled and before any appliances are used?
I checked the pressure at the boiler, based on the directions that came from Lochinvar. At 12.4", it is within range. And to reiterate: the problem is when the tank was recently filled; it seems fine after the tank is a bit lower, and once it is working again I'll take another pressure reading.
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Is there a high gas pressure switch on the boiler?No, I don't have that.
I did another test: simply pinching the line will make it also light. Super strange..
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I had a run of issues with air in the LP tank after filling a few years ago. sounds similar. things a tech can check, static and dynamic gas pressure (12.4 is static according to your comment, what does it drop to at ignition high fire etc, needs to be within range but record the number), combustion (with analyzer set per the manual) venting clear and within spec and not holding any condensate
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are you measuring the pressure while gas is flowing and it is failing to ignite?
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Interesting! It seems to consistently happen though, right after a fill up. Maybe air would get in each time?
I'm hoping to not hire a technician and try to solve it myself.
Yes, I believe I measured the static pressure, per the manual's instructions: unscrewing the right hand port one full turn and using a manometer. I do not have an analyzer to measure the combustion. The vents are clear, and don't seem to be holding any condensate.
Even if I measured all these things…and assuming the pressure drop is within range…what else could be changed or modified to look at or replace? I'd hope that simply replacing the gas valve assembly would have fixed this, but it did not.
Other data points: I'm at ~6600' elevation.
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No, I have not done that, but I can. What should I look for, other than being "within range" of what the manual says? What would be a solution if it isn't "within range?"
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The item to look for when testing the dynamic pressure is that you don’t want to see a big pressure drop when the boiler ignites. Some boilers can’t tolerate more than a 1” pressure drop.
And if you find that there is a large pressure drop, the cause may be a bad pressure regulator or the piping from the regulator to the appliance (boiler) hasn’t been sized properly and the pressure drop is too high for the boiler to tolerate. These negative pressure gas valves are finicky.8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab
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or liquid propane is getting in to the regulator or there isn't enough space over he liquid to generate that volume of gas at that outdoor temp. does it happen after all the gas appliances have been off for a while or only after other appliances have been drawing from the tank?
if the dynamic pressure drops a lot, probably time to talk to the propane supplier about the tank setup.
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That li'l clear plastic tube is the vent for the gas valve regulator, it allows the gas valve to compensate for the pressure in the sealed combustion chamber. I'm having trouble seeing how the tank level and that would interact.
Take the outlet pressure of the gas valve (same procedure, but use the other teat on the valve). Make sure to zero you manometer before the inducer starts, in fact zero it with no hoses use attached to it, then watch the pressure thought an entire cycle. It should start out zero with the furnace idle, drop slightly negative when the inducer starts, then jump up to high fire (should be on the nameplate, but not the natural gas number, which is 3.5 in wc).
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Do you have the high altitude model?
A combustion analyzer is needed any way you look at it.
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