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Weil Mclain HE II-4 Still Kicking

Part I: HE II-4 with a 1013-200 replacing the 1992 Original in 2017 when WMc told me it was the cause of the then current issue I was having (wasn't - that ghost of an issue was a bad terminal on the gas valve shutting down the supply whenever it felt like it). The problem at hand:
I know I NOW have a faulty differential pressure switch. It may or may not have been before my trying to diagnose. I have since disconnected the hoses and are manually closing the circuit once we get to that stage. I understand it needs to prove a draft for combustion before going on. Turn power on & green goes on along with momentary light on pressure switch circuit. About 6 seconds later the call for heat (at least 1 of the 5 zones are calling!) AND Limit circuit closed - blower powered light MOMENTARILY comes on (3rd red LED). That's where it stops with just the green light on. I have tried many on off cycles of main power and occasionally it will continue to the next step unless i forget to close the differential circuit (bypassing manually). It will cycle on and off for hours, give us plenty of heat & hot water, then go back to the "I ain't gonna be easy to start again" mode. When appropriate LEDs come on there is movement of the fan and power to the circulating pump as long as a zone valve is open.

Part II - It seems the original spec for the air pressure switch unit was .95 WC - model 511-624-510 UPC 645220425235. I'm seeing the same part number out there with a 1.00 WC rating. Is this going to make a difference with a replacement?

Thank anyone who can help keep this caveman's dinosaur going.


  • Zman
    Zman Member Posts: 7,573
    edited November 2021
    Do you have a bad differential switch or do you have a perfectly good switch doing its job and inadequate airflow? Any chance you could put a manometer on it rather than changing parts?

    Years ago I was snowmobiling with a buddy when his machine went dead. We were clever enough to discover a "bad" throttle sensor switch. We bypassed the switch and fired it up. I can still close my eyes and see his unmanned snowmobile pinballing through the trees at full throttle. Ever since, I think a lot harder before bypassing safeties, even for diagnostics. :(

    If the switch ends up being the only problem, .05" WC should not make any difference.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein