I apparently have the most unsolvable boiler problem

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I have a 23-year-old weil mclain GV series 3 boiler.

So far I have had 5 professional tech companies come in each one of them said, "oh this is 100% the issue"... and all of them have been wrong!!

I've probably spent accumulative of 8-10 hours on the phone with well McClain tech support, driven all over the Denver area & Internet for parts, paid tech call fees,.etc.

I've replaced:
-Gas valve
-Pressure switch (high altitude as I'm at (7000')
-Mother board
-H20 temp return sensor
-Taco motos x2

I've done:
-Air & Vent pipes in/out at both house & boiler checked for obstruction
-check heat exchanger window for obstructions
-check and clean the orifice plate for obstructions
-check that blower motor spins freely (when orifice plate was off)
-check and clean the cone for obstructions
-flushed the heat exchanger with water to check for obstructions

Issue: The boiler goes through the startup process, all the lights properly come on in order and the moment it wants to flame on it snuffs itself out and the flame light and pressure switch lights shut off and then it starts the entire cycle again and will never get past that cycle.

BUT I can get the system running IF I jump the pressure switch, but obviously once it shuts down after reaching its temperature it can't auto restart it with a jumped pressure switch. so I daily manually milk this thing along & jump the pressure switch when I want to make sure there's enough hot water in the house.

I dare someone to solve this.
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Well-Known Member
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Peace valley missouri
Lp or nat gas? Sidewall vented? Where is the makeup air coming from? Has the negative gas pressure valve set at -.2" ? Is the correct orifice plate installed silver for nat red for lp? High altitude air pressure switch installed? After jumping out air pressure switch and boiler is firing have u put a meter on the switch to see if it's closed?


Licensed plumbing contractor
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San Francisco Bay Area
I don't know your unit, but, if there is a flame sensor next to the ignitor, pull it out and scrape it off with hard edge like back of a knife. Emery cloth sometimes is good, but scraping is worthwhile.
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