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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I am working on a 10-yr old muchkin boiler (no nameplate anywhere

Customer Question

I am working on a 10-yr old muchkin boiler (no nameplate anywhere to be found, just an old hx stamped plate with a date and mfg serial, which munchkin cannot use to lookup model num).
It fires, gives a nice-looking flame for around 2-3 seconds and a good flame sense current (3-4 micro amps). The kinda does a weird 'farting' noise and flames out. HTP tech support told me that the burner was clogged and I took it out and cleaned it. The HX does not seem too bad, and I do not see any buildup of condensate. I'm thinking the gas valve. It's a honeywell VK8115V. I measured output pressure. During ignition it's like -4", then when lit around -0.05 and increases (to around -0.04) and flames out with a sputtering sound. Any idea. Also, I'm a decent boiler tech, so pls only answer if you know this particular valve/boiler inside and out. Thanks! David
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.
Welcome
This not an answer unfortunately... at 10 years old that boiler was built in Munchkins earlier days, you will be hard pressed to find anyone who knows that boil here or anywhere.
Your guess on the gas valve is at least 50% possible.. the other option is the printed circuit card... at 10 years old in that environment is approaching or beyond a normal life span.
Stress test the printed circuit card.
Use a hair drier to slowly and gently warm the card to 120F (warm to the touch but not hot and not over 140F)... if you get any change in behavior that means the card is bad...
A micro crack has opened in the printed circuit at a solder joint, or inside its CPU in that case .... or a short circuit has developed as the card expanded when you heated it.
Constant expansion and contraction as these electronics heat and during their duty cycles over the years is what wears these cards out.
It is also a good idea to replug all of the connections in the unit, that burnishes any oxidized terminal connections and will sometimes solve the problem, especially at the printed circuit card and in any sensor molex connectors. Do that with the power off to the unit of course.
These cards are also damaged by Electrical Spikes caused by power failures and lightning. These high voltage spikes can literally explode the fine 'wire' connections inside the chip. There is also a shunt type device, often printed on to the card that allows a high voltage spike to arc across to ground harmlessly, some of these can wear out after a few times and allow the high voltage spike into the rest of the card and the CPU micro-circuits. The high end printed circuit cards use a large capacitor like device, or several in parallel, to capture and release such surges, these do not wear out.
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If you think that was helpful at all and worth continuing with let me know and we can continue.
.
Customer: replied 1 year ago.
The board seems to function ok (sequences the purge, gas valve, burner fan, and has flame rectification current for at least a couple seconds). I don't think it's the board. Thanks, David
Expert:  Phil replied 1 year ago.
A bad board will very often function perfectly..... until it warms up with current flow, and *then it will malfunction.
in those cases it malfunctions because the card *expands slightly, opening *micro cracks in the card or processor that were closed and functioning well before it was energize or had warmed up with use.
That is also caused by resistors in the process of failing (by overheat).
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Customer: replied 1 year ago.
(Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from yo. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  Phil replied 1 year ago.
I need a well focused, well lit, photo of the boiler wiring diagram, taken from close up and straight on.
Use the 'attach files' link at the bottom left of this dialog box so that I can work with it before discussing the issues live.
That will be the most effective approach.

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