Munchkin 140MLP R1 Intermittent Gas Leak
Munchkin 140MLP R1 installed ~2007-2008. Three and a half weeks ago noticed a fairly strong propane odor in the family room adjacent to utility room. Evacuated house. Turned off gas at LP tank. Called gas company. Gas company technician used his gas detector and narrowed it down to gas leaking at/near gas shutoff valve internal to boiler (after removing cover). Fortunately, we have a wood burning fireplace so we were able to heat the house with it until replacement Dungs 7250P-451 gas valve assembly arrived. Installed gas valve last Monday evening, 9 Dec, and called gas company Tuesday morning to schedule an inspection that day to ensure no leaks due to the install. Technician arrived, without gas detector, and checked gas line connection at valve with leak detection fluid around the fitting. He also connected a gauge on the regulator outside the house to check for leak down. He stated no leaks observed, so we left the gas on and began using boiler to heat.
This morning, went into utility room and noticed propane smell again. Not as strong as last time, but obviously there. Turned off shutoff at boiler, then turned off at LP tank. Smell does seem to be eminating (based on nose) from the Dungs gas valve area.
So, now I'm scratching my head trying to understand what is causing the leak. Did I get a defective replacement valve? Is the controller defective and not closing the valve entirely when it should be?
Any troubleshooting assistance would be greatly appreciated.
Comments
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A few installation pictures that show as-is with new gas valve installed. Power removed.
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I'm just grasping at straws here but the screws that secure the 90 degree flange to the gas valve appear to be damaged on the hex as though the installer used the wrong allen wrench.
Since this is aluminum, I would expect the torque on those four is somewhat critical to seal properly. Obviously this cannot be done without the proper tools.
It does appear that a gasket was utilized under that flange. Confirm that it is new and the face of the flange was perfectly clean from the residue of the old gasket.
It's highly unlikely the gas valve is defective…………but not impossible, of course.
These devices are not like cars where you can just slap them together and they work.
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Screw heads are not damaged. None are loose. There was no gasket when old valve was removed, nor was a gasket provided with new valve assembly. Munchkin manual does not indicate a gasket is included at that joint. See figure 33 of manual linked here;
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Also, gas company technician checked that specific fitting with leak detection fluid.
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there is an o-ring that seals that joint.
did you set the combustion on the gas valve? these gas valves don't come set up. you could be getting delayed ignition and getting the smell of propane thru incomplete combustion.
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Not likely but not impossible to have two gas leak problems at one time. You need to get a tech in to check this out.
Propane can be nasty.
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Hmm… regarding your second comment, no. I did not make any adjustments. Thought the valve was "plug and play". Assumed my due diligence of having gas technician inspect for leaks warranted my DIY attempt here. Also makes me wonder if the valve I removed was actually defective and might have just required adjustment. Looks like I'll be calling boiler service company tomorrow morning to schedule service. We had them out just a couple months ago to look it over before the cold temps settled in and they said it was "all good". Not sure if poor settings on the old valve are something they could have detected during the previous service call?
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Follow up on this. Tech came out to service the new gas valve and asked a number of questions to understand the original issue (that drove me to replace the valve) and then the subsequent smell following installation. His comment was that the valves are generally setup fairly close to spec, but do need some "fine tuning". He also noted that if there were major issues with the settings that there would be audible clues while the boiler is running. He referred to this as "trumpeting" of the intake and/or exhaust. When he ran it upon initial inspection, he said it sounded fine and visual appearance of flame appeared "normal" (he mentioned some things about the flame that he was looking at, but I forget the specifics).
He ended up noticing two screws were loose on the "duct" that routes from the blower to the combustion chamber (not sure who/when this happened as I didn't touch these during valve replacement). The loose screws were near the blower to duct interface, so we suspected that was where the gas smell was coming from. The screws appeared to have been cross threaded at some point, so they wouldn't tighten. Tech left and we agreed that he'd try to find a new fitting, but offered to come back (to further inspect and run combustion analyzer) if I was able to get the threads cleaned up with a tap and the screws back in and tight.
I was able to get a 5mm-0.80 tap and cleaned up the threads in both holes (thankfully they were drilled through the part, so was able to access from the front side). After the threads were cleaned up, screws were installed and tightened.
I've ran it a few times since tightening those screws and continue to get a faint gas smell. Have had the boiler and gas off while not test running it. Some observations;
- Faint smell is only AFTER the boiler stops heating when thermostat ceases the heating command.
- The blower fan does run for a short period after it stops heating.
- There are no unusual sounds from pipes.
- Visual inspection of majority of exhaust pipe shows it completely clear (looked in exterior open end that spans width of house to elbow above boiler).
The tech that was out said that the only way for gas to exit the valve is if the blower is running and creates a negative pressure on the downstream side of the valve, causing it to open and allow gas to flow. But is it possible that the control board is not closing the valve after a heating cycle causing gas to continue to slowly leak?
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I had a negative pressure gas valve pass gas to where it looked to have a standing pilot. It would not fire as it threw up a code that indicated that flame was already present.
This was on a brand new HTP Phoenix WH.
Factory said impossible, can't happen………replacement valve corrected issue though.
If you smell gas again and unplug the power to the valve and it stope the smells then you may have some phantom voltage getting to the valve to partially open it.
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That's a possibility in which case you might need a new circuit board. You have the original 925 board (red transformer) and there have been upgrades to the 926 board (black transformer).
While not specifically dealing with the same issue as you have, the 926 upgrade seems to fix many problems.
My notes from Steve Ebels:
A 140 we installed in 02 IIRC. After troubleshooting everything, and I mean complete disassemble, cleaning, tuning,flame sensor, pressure switch we still had the lockout problem. Chuck told me that the cure would be a board update to the 926 and he was right. Installed it and the boiler runs fine. In fact better than it ever did. It lights off at a little higher fan speed/input and then modulates down to minimum which really makes a difference in reliable starting. Modulates better, steadier fan speed during operation, flame sense reading in the 12-14 UA range. Lights up and stays lit just like it should. It really wasn't all that expensive as boards go.
And from Wayco Wayne:
The new 926 board has a much longer post purge. The 140 has a problem that after it shuts off heat would rise from the HX and melt stuff in the flu blower. The new board runs a 90 second cool down so the HX cools enough so that wont happen. Upgrade both refractories while you're at it. It makes for a nice upgrade. The new board also raises the voltage to the flame sensor and makes the sparker a second flame sensor. Say goodbye to any F-09 problems.
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 slab0 -
Don't you just love it when the factory says" We have never ever had that problem before, can't happen"
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Has anyone checked the incoming gas pressure? What does the venturi look like? Has the heat exchanger been cleaned lately? Is the burner gasket OK? Has combustion been set up?
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