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Help with Weil McLain CGi Gold Boiler Short Cycling

Canadave Member Posts: 8
edited January 2023 in Gas Heating
Hi there,

I have a Weil McLain CGi Gold boiler, installed in 2010. It will start, pilot will light, main burner will fire, but after that it becomes very unpredictable. Sometimes it will run just fine through to the end of the cycle and do everything right. Other times it will struggle through with a clicking noise and the gas supply to the main burner cutting/refiring after half a second (assume this is the flame sensor signal failing). Other times the boiler will just shut down completely mid cycle and will not attempt to refire for an hour.

When it shuts down, the TSTAT/CIRC and LIMIT LED lights on the 1107-1 control module are SOLID red. The Power LED is off. Nowhere in the manual is this combination discussed or addressed.

This problem has been occurring for a year and a half or so, I initially successfully resolved it by disassembling and cleaning the whole burner assembly and specifically cleaning the flame sensor. Ran fine for months after this. Fast forward to this year, same problem occurs, clean flame sensor, resolves for a while then returns. Figured the flame sensor was done so I ordered a new pilot assembly which includes the flame sensor and had it professionally installed 3 weeks ago. When in operation I can see the flame sensor glowing bright orange. The problem is persisting and I am out of ideas. Often times if I cut the power to the boiler and switch back on after a minute it helps, but this is not a sustainable solution when it's below freezing and I'm not home.

Wondering if anyone has any experience with these circumstances or advice on what to try next? I was thinking it could be the rollout fuse?

Any help is greatly appreciated, thank you kindly in advance.


    JUGHNE Member Posts: 11,021
    Roll out fuses are usually one shot and they open, must be replaced.
    Plugged flue vent safeties are manually resettable.

    Neither of these sound like your problem.

    Could you post pictures with the cover removed showing all the components and also of the wiring diagram.
    Someone here is most likely familiar with this boiler. I am not.
  • Canadave
    Canadave Member Posts: 8
    Here are some pictures I hope will help
    JUGHNE Member Posts: 11,021
    The pressure switch has 2 hoses, check that they do not have water in them.
    And check where they connect to the boiler that that opening is clear.
    You need a manometer and a volt meter to test the switch.

    Then the flame sensor is 1/2 of an electrical circuit, the other 1/2 is ground which could be established thru the pilot burner or sometimes a separate wire.

    Is that the original control module?

    I would reseat all electrical connections, especially the grounding starting in the power junction box.
    For all others simply unplug and replug to cut any minor corrosion.

    That is about all you can do without meters etc.

    Others may be more help.
  • Matt_67
    Matt_67 Member Posts: 284
    I would also check the pressure switch tubes and port. I experienced a similar behavior on a newer cGi that was pressure switch related, you’d need a tech there with a manometer and multimeter to check that though.
    EBEBRATT-Ed Member Posts: 15,353
    I have seen pressure switch hoses and connection ports with dirt, dust or bugs in them. I would disconnect all the wiring 1 wire at a time. Sometimes 24-volt wiring gets slightly corroded it will cause intermittent problems. It could also be the control
  • Canadave
    Canadave Member Posts: 8
    Update: problem came back while I was away for weekend.  Saw temperature drop via Google nest thermostat.  Set at 19C it reached 16C before it magically recovered to 19 by the time I got home.  Decided to check grounding from service switch.  Found the ground wire from the switch attached to NOTHING in the junction box.  It was positioned such that it make have been making contact with the steel cover plate which may have provided some level of grounding? Either way I screwed the ground wire from the switch firmly to the ground screw in/on the junction box.  Going to see how this works out.  A very knowledgeable friend says the control module is going, but I know grounding is very important for the module per the manual.   Thoughts welcomed, for now I wait and see.  Thanks to all for the help so far.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,618
    edited January 2023

    What is the chance that other screws and wiring connections have a little corrosion build up?
    The flame sensing circuit is extremely low voltage. It depends on the electricity from the control module>going down the wire>then jumping across the flame> then using the metal chassis of the heater as a ground conductor.>back the the control module from the ground screw that holds the control on the boiler metal jacket.

    When I look at some furnaces and boilers that are in humid rooms I sometimes see that all the screws that hold the parts together have a corrosion build-up on them. Just loosening and tightening electric terminal screws, Removing and putting spade wire connectors back, and un-plugging and plugging connectors back in will remove the corrosion and make a better electrical connection as @JUGHNE suggested.

    One final fix I found successful: is to use a ground wire attached to the pilot burner screw, and connect it to the mounting screw of the control module that makes the chassis ground connection. That way you will eliminate all the corroded metal heater parts that may be a part of the bad connection.

    Mr. ED

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • ethicalpaul
    ethicalpaul Member Posts: 5,628
    Does your nest have a C wire? Regardless I'd replace it with a "dumb" thermostat for awhile to rule it out.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • Canadave
    Canadave Member Posts: 8
    Everything running beautifully since the ground wire has been connected in the junction box. What a terrific community and forum here. Thank you everyone!
  • Canadave
    Canadave Member Posts: 8
    Update: the problem has returned.

    I even added the dedicated ground screw as recommended.

    It really seemes to be a crapshoot as to when it will work and when it won't.   It will do 5 full cycles without a problem and then not even get past the pilot stage to light the main burners a few hours later.

    I have ordered a  new control module in the hopes that is the problem.  A friend of mine in HVAC said it is common for the boards to be temperamental when the are giving up the ghost as opposed to flat out dying.

    Many thanks to all who have offered assistance,  I will keep you posted when I swap the control modules.

  • Wrightlb
    Wrightlb Member Posts: 3
    I had a similar issue with similarly aged boiler. A lot of chattering relay noise and the boiler rapidly starting/stopping. I replaced the power head on the offending zone valve and the problem has cleared up.
  • Canadave
    Canadave Member Posts: 8
    Upon rereading I think I may have misinterpreted @EdTheHeaterMan s advice because I just ran a ground from the pilot burner to the chassis.  I have rewired to do it from the pilot burner to the chassis ground on the control module.  See pic.  Let's see how this works. White wire running vertically is the new ground, i just layered it on top the existing chassis ground...
  • kcopp
    kcopp Member Posts: 4,397
    that smacks of a bad Molex connector.
    Check all those little wires in the plastic plugs. The real pain is that they work sometimes and sometimes dont.
  • Canadave
    Canadave Member Posts: 8
    Boiler has been running bulletproof since I implemented @EdTheHeaterMan 's suggestion. Going to pick up a control module to have on the shelf in case it ever gives up. Cannot thank you all enough for helping me navigate this issue, the "professionals" I have had look at it never so much as once mentioned grounding, which clearly seems to have been the problem. Big love from the north!
  • Canadave
    Canadave Member Posts: 8
    Update: Replaced control module and everything is working fine. Right before I replaced the module the boiler was having a very difficult time running, was not even recognizing the pilot flame, or clicking like crazy and the main burner was popping on and off. I feel pretty certain that since I changed nothing else when it was behaving this way that the control module was the root of my issues. Thanks again to all for the tips. I'll leave you with one. If you ever need a 1107-1 UTec control module, buy it online from the states, I paid $350 Canadian for what sells for $816 plus tax = $922 here.