Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Weil McLain boiler

jkimbllin Member Posts: 3
I have a Weil McLain CGs boiler that is not working. I need some help with my in floor heat. Have replaced the safety relief valve , psi pressure gauge and Taco circulating pump all due to sticking, not working, overheating, my boiler will fire for 5 minutes and shut down. I noticed on my new psi gauge the water pressure was zero so I put a hose on the and filled to 15 psi. Agin fired the unit and quick after  5 minutes. Next day saw the PSI was zero so thought to replaced the valve again- same thing happened. I question if the pressure relief valve is bad, however it will fire and shut down after 5 minutes. Oh by the way, have an expansion tank side wall leaking , so replaced that as well.


  • mattmia2
    mattmia2 Member Posts: 7,734
    Sounds like you have either air still in the system or a leak and a bad pressure reducing valve or the supply to it is shut off.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 5,632
    edited May 2022
    Are you unable to find an experienced boiler repair professional? It sounds like you're throwing parts at a problem without the ability to diagnose where to look first. There are many professionals that do that, that is why I'm asking if you can't find and EXPERIENCED pro.

    If you are just doing this because you a DIY type of guy/gal, then you may find that you will spend more money on unnecessary parts until you finally get lucky enough to get the right one.

    To be clear.
    You have a Weil Mclain CG boiler connected to some type of floor heating emitters.
    You have a new expansion tank
    You have a new pressure gauge
    You have a new relief valve.
    and you have no heat.

    The high limit is working because the burner stops operating after about 5 minutes of operation.

    The water is not circulating thru the emitters, If the water was circulating, the boiler water would not get hot enough to shut the burner off by way of the high limit so quickly.

    I can see many other causes for no heat.

    Water not circulating thru the emitters because
    1. They are air locked and need to be purged of air
    2. The circulator is not operating (but you just replaced that) so see if the wired are connected properly
    3. There is no power to the circulator motor
    4. A valve is closed
    5. The expansion tank is overloaded or the diaphragm type tank has the incorrect empty air pressure. (Must be measured before connected to system)
    6. You do not have a working automatic water feed valve (AKA pressure reducing valve)
    7. You have a leak in the piping from the boiler to the emitters or the in floor tubing is leaking
    8. There is debris or sludge clogging the piping or emitter tubing (in the floor).
    9. You don't have the knowledge that an experienced professional has to decide which one of the above is the problem or if it is a completely different problem.

    Does that about sum it up?

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • pedmec
    pedmec Member Posts: 718
    is your in floor heat an old copper in slab system?
  • jkimbllin
    jkimbllin Member Posts: 3
    The lines leading in the floor look to be a plastic type material
  • jkimbllin
    jkimbllin Member Posts: 3
    It is unfortunate but the tech I had out to check the system wanted to change the induction motor out because it would not start. The motor was in the range of $600-$700.  After he left I checked the motor out got it started and it continued to fire for the brief 5 minutes . The lines get hot but shut down. After that I questioned the owner about replacing the motor and he came out and said the relief valve was sticking , gauge was not working and bladder tank had a pin hole leak. I replaced those , but still have the same issue of firing. I did add air to the new bladder tank with stated it needed 75 psi
    EBEBRATT-Ed Member Posts: 13,440
    The expansion tank does not need 75psi for starters. 12-15 psi is what you need. But you have to remove the bladder tank from the system and then check and adjust the air pressure while it is disconnected. Then reinstall the tank put 15psi of water pressure in the system and start from there
    JUGHNE Member Posts: 10,570
    Your induction motor sounds to be failing.
    It may slow down and drop out the pressure switch that controls the burner after your 5 minute burn.

    Are you sure the pump is running?
    Can you post a picture showing the pump from the side of the boiler?
    Back up for photos.
  • jkimbllin
    jkimbllin Member Posts: 3
    edited June 2022
    Looking for Mr. Ed Heating Man
    Started by adding water to 20 psi, add air to the expansion tank 20 psi ( TACO rep suggestion) times the boiler from first fire 10 minutes 21 seconds
    Temperature rose to 165, bypass open to about 30  percent 
    JUGHNE Member Posts: 10,570
    You should stay on your original posting.
    If you add to it then it goes to the top of the page.

    How about those pictures of the pump?
  • Erin Holohan Haskell
    Erin Holohan Haskell Member, Moderator, Administrator Posts: 2,073
    @jkimbllin, I've merged your two posts into one here.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 5,632
    edited June 2022
    To bring everyone up to date. All good now. We had a communication error. OP was using incorrect name for parts. Also @jkimbllin has a better understanding of how the system works. It took some back and forth dialogue over the past 2 days, but I believe it is working..

    I have to say if the professional contractor who recommended the new parts including the Inducer Fan motor, the Pressure Switch (Not Pressure Relief Valve), Expansion Tank, and Gauge were to look at this discussion, You might ask yourself "IF YOU REPLACE THAT EXPENSIVE PART AND IT STILL DOES THE SAME THING, WHAT WILL YOU LOOK AT NEXT?" (one of my favorites). If the answer is less expansive, do that first!

    The OP purchased and installed the new #15 Expansion tank with diaphragm.
    With no experience in these matters, the OP pumped up the tank to the "Working pressure" before installation. This was a major cause of "no heat". water leaking and zero pressure and possibly no water circulation in the heating system.

    Since the boiler would go off by the High Limit, the OP, and possible the professional, felt there was something wrong with the pressure switch or the inducer motor or both. Hence the need for a new pressure switch that the OP called a pressure relief valve.

    Once I realized that the problem the OP was tryig to solve was that the burner stopped and would not come back on, I calculated that the boiler was at the High limit and hot water was not circulating. I was able to talk @jkimbllin thru the process of getting the new expansion tank to 20 PSI then fill the boiler to 20 PSI and see if the water would circulate. It did, and the rooms heated up the 75 degrees while trying different bypass valve settings from closed to open to partially open, before we stopped for the day. OP set the thermostat to 68° and will let the thermostat operate the system as usual.

    It appears that the boiler is oversized and the burner will cycle off of the high limit to the tune of about 50% run time 5 minutes on and 5 minutes off. There are only about 4 or 5 loops (visible) that operate by 2 different thermostats.


    Did all this on PM to keep on task so other Unnecessary posts did not distract. But I know that many here want to hear about the success stories.

    Respectfully submitted,


    EDIT: OP was in touch with Taco tech support in this also. There is one circulator with the motor mounted on top of the pump (not preferred but acceptable) that is why we decided on the 20 PSI cold static pressure. So the water would be able to lube the top bearing per Taco recommendations. Personally I would rotate the pump 90° to put the motor on the horizontal, but that's just me.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics