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Weil McLane CGi Series 2 Boiler is Cycling

zzfix Member Posts: 5
I have a Weil McLain Series 2 GCi boiler. It is operating fine for about 3 minutes. After that, it shuts off. The thermostat is still calling for heat (red TSTAT LED is on - not flashing). after about 10-12 minutes, this cycle repeats. This is happening continuously. During the 3 minutes of operation all the LEDs are on (green Power, red TSTAT, LIMIT, PRESSURE SW, FLAME). Any clues?
- Thanks


  • Tim McElwain
    Tim McElwain Member Posts: 4,493
    Do you have the United Technology 1107-1 control module on this boiler? If so is it a CGi 3, 4 etc boiler? The reason I am asking that is you could have a pressure switch problem and depending on the boiler size there are different set points for pressure on the switch. At any time do you observe any lights flashing on the control module?
  • zzfix
    zzfix Member Posts: 5
    Thank you for your quick response. It is an 1107-1 control module. The boiler label call it a Gold CGI. The schematic bottom right title is CGs CGi Series 2 Part Number 550-225-070/1101. I suspect the pressure switch as well. I will check the pressure switch setting tomorrow. There were no flashing LEDs, that would have been too easy :)
  • Tim McElwain
    Tim McElwain Member Posts: 4,493
    Pressure switch setpoints are as follows:
    CGi 25 and CGi 3 1.79 " WC
    CGi 4 1.40" WC
    CGi 5 1.12" WC
    CGi 6 and CGi 8 0.80" WC
    CGi 7 0.75" WC
  • zzfix
    zzfix Member Posts: 5
    Thank you for the info. I think I understand what is happening.
    To begin with the boiler is a CGI 4 Series 2 model. I have 2 of these boilers in the 2 family house. I exchanged the (Honeywell) Pressure Valve and the same thing was happening. I shut the boiler down for a while to let everything cool down and then restarted it. Once running, it stayed fully on for a period of 15-20 minutes this time. After that, it continued to cycle as before: 3 minutes on then about 10-12 minutes with only the Power and Thermostat LEDs on. Specifically after a few minutes the FLAME indicator goes off and several seconds later the other 2 LEDs go off (PRESSURE and LIMIT).

    While in that state I hear the circulator pump still slightly humming. Is it very quiet when it runs? If so, this may be a normal mode of operation. The water may be hot enough to allow to circulate without heating by the boiler, so the 3 LEDs and associated functions are not needed then.

    the reason that makes sense is that when I shut the system down for a while and it cooled down, it then went on and stayed on until the water reached the right temperature, which took much longer than the 3 minutes.

    I also noticed the same shutdown of LEDs for floor 2 a couple of times.

    While doing this troubleshooting I cleaned out the burners, readjusted the water temperature settings, and opened the relief valves to make sure they work.

    Does this make sense?

  • wmtandson
    wmtandson Member Posts: 62
    SOUND S like your ready to hit the road doing service work
  • Tim, is it possible the boiler is going off on high limit caused by lack of flow?

    Zzfix, did this just start happening? Are there any before (when the boiler ran without cycling) and now symptoms? When you fire the boiler from a cooled down system how fast does it come up to temp (and what is the temp) before it shuts down?

    A "humming" circ does not necessarily mean the impeller is spinning. Might have a broken ceramic shaft or stuck rotor.
  • JAdams
    JAdams Member Posts: 24
    edited January 2015
    I had the same problem with one recently. The trouble was two things: Although the inducer was providing enough draft for the pressure switch, at first, the motor would heat up and slow down in rpm's closing the pressure switch. Also, the gasket on the blower assembly was leaking. The fix, installed a new blower assembly, comes with gasket. If you choose this fix, it would be wise to clean the burner cone at the same time.
  • unclejohn
    unclejohn Member Posts: 1,751
    We must now assume that you never had a no heat situation ?You did every thing right except open the relief valve. Never open that.
  • zzfix
    zzfix Member Posts: 5
    Thank you all for the responses. This is a great forum.

    I don't live in this 2 family home but the tenant on the 1st floor is very attentive and seems able to clearly explain what is going on. As far as I know there has not been a "no heat" situation. The house was very comfortable when I was there.

    As far as coming up to temperature from a cooled down state, I did not time it but I am guessing that it took about 20 minutes and the temperature went from about 150F to 180F.

    I checked the exhaust hot air of both boilers while they were both running to "feel" the amount of air pressure coming out to make sure there were no air clogs. Both vents felt about the same in air flow and pretty hot temperature.

    The temperature limit switch is now set to 180F and the gauge reads 180 when both boiler systems are running. The boiler systems include integrated water heater tanks that have settable temperature limit switches as well. I adjusted those to their nominal settings (160F or 180F, I don't remember).

    About the pressure relief valve, I had one replaced a year ago on the other line because it would not stop leaking so I thought testing the old one is necessary occasionally. It took a while for it to eventually stop dripping - should have left it alone.

    I'm still wondering if the system is working correctly as it is before continuing to troubleshoot further. The forecast is to get very cold this coming week.

    As far as a second career in HVAC repairs, I am naturally curious about how all things work (not just HVAC) and always prefer to understand what is not right before deciding if I should tackle myself or get expert help :)

    Thank you all for your comments. I would love to hear from Tim as well.
  • Tim McElwain
    Tim McElwain Member Posts: 4,493
    Do you have the Installation and operating manual for the boiler? I will not be readily available this week as I have day and night classes I am teaching.
  • zzfix
    zzfix Member Posts: 5
    yes I have it. It does not explain this particular situation