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.

High Limit - Limitations

Terry Member Posts: 186
Unfortunatly the make of the controller will give away the manufacturer.. oh well. The Micro Control is a SENTRY 2100, Used on the NTI Legacy Boilers.

I am planning to specify an aditional probe style high limit be sold with each unit and will instruct to remove snap disc & put probe style in as the safety device.

I have tried the ladder/chain of command routine and have received little to no support. Even our boiler safety department (ABSA) hasn't responded with a position either way. I also sent CSA information to find out how this passed (MICRO-CONTROL as safety) and recieved nothing back.

I wish us Canadians were a little more aggresive like our U.S. Big brother! - u guys rock!

"May the enemy never see you coming"



  • Terry
    Terry Member Posts: 186
    Questionable High Limit

    Have a Boiler made by manufacturer "X".
    HIgh Limit is a snap disc gear clamped to supply discharge pipe buried in behind burner and very close to heat exchanger.

    Had customer no heat calls - appears the limits are tripping prematurely and being manual rest devices, the installer has to return to remove top of jacket to access high limit to reset.

    Asked Manufacturer for solution. Answer was to "loosen" the gear clamp afixing this safety control to the pipe. I questioned the integrity of this advice and was told that the limit could actually be removed, since it was a "redundant" safety device and the MICROPROCESSOR's internal high limit was the TRUE safety device.

    To my knowledge, a microprocessor CAN NOT be considered as a prmary safety device. Operator only. I also thought that the safety device has to be a mechanical switch with a probe IN the piping/HE.

    In the meantime I am suggesting to move this limit to the outside of the boiler to keep it out of the internal residual heat that builds up inside the jacket.

    Any thoughts or positions ???

    Thanks in advance - and hopefully see you all at the 2003 Foothills conference Apr 3-4 in Sunny Alberta.


  • Steamhead
    Steamhead Member Posts: 16,712
    I see many \"Surface Aquastats\"

    on older coal-converted boilers but have never heard of a strap-on limit on a newer unit. All the ones I see on newer boilers are immersion type. I would assume this type of limit was acceptable on conversion jobs but wonder about newer packaged units.

    I agree that one should not rely on a microprocessor for the high-limit. It sounds like the strap-on unit was an afterthought, installed when someone pointed out the above.

    Putting a manual-reset limit in such an inaccessible place doesn't sound right to me. Maybe you need to talk to someone higher up in the chain of command.

    An alternative might be a tee on the supply and a very long immersion well that could reach all the way into the boiler sections. Not knowing which boiler you have, I can't be more detailed than that.

    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Some United Technology

    boards have a plug in on the board for a thermister which is strapped on to the piping in the boiler. It is called a "Water Temperature Sensor", I would assume this is what they are talking about as the thermister is directly tied into the microprocessor control board. Those systems do also however have a regular boiler limit into a well on the boiler.
    What are some of the numbers and makes of the controls on this system?
This discussion has been closed.