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Suitable replacement combustion air switch

The pressure switch on my Fagor FE-18E boiler has failed.  This is a European boiler from a company that closed the factory in Spain a year ago and cannot provide parts.  The two-port switch is stamped 82/66Pa (Pascals), which converts to 0.33"/0.27" W.C.

I'm looking at replacing it with a RobertShaw 2374-495, a 2-port, adjustable pressure switch.  It's supposed to be adjustable in the range 0.25" - 1.0" W.C., which would include the range I need.

A photo of the label on the failed switch is attached. Searching for the FAGOR part number N49G010M3 only finds it sold by a company in Germany for €86, about $116, but the company doesn't ship outside of Germany. On the other hand, the Robertshaw part can be found for as little as $24 making it the switch of choice if it works.

I understand that this is a safety item and that an OEM replacement is preferred, but that doesn't seem to be an option. The furnace is in Mexico, where we're a bit more casual about liability in the event of an accident, making me want to try an adjustable switch.

Your thoughts please?


Mark E.

Pátzcuaro, Mexico


  • RobG
    RobG Member Posts: 1,850
    Pressure Switch

    Have you checked to make sure that the pressure switch is not just doing its job? From one of your earlier posts you stated that you were getting flue gas reversion. I can't claim to know anything about that brand of boiler. A pressure switch is a pressure switch though, make and break, brake and make (unless the Spaniards have created something that I don't know about). Do you have a manometer to make the proper adjustments?

  • MarkE
    MarkE Member Posts: 14
    Re: Pressure switch

    Hi Rob,

    I don't recall ever posting about flue gas reversion.  However, I did try cleaning the system first:

    I removed the copper-finned heat exchanger and cleaned it of the accumulated fine white powder by rinsing with hot water, per the manual. The squirrel fan blades also had some powder on them, which I was able to brush off.  From the combustion chamber to the stack exit at the top of the boiler, it's as clean as a whistle. I disconnected the exhaust stack so there's no back pressure there. I even removed the ceramic venturri and cleaned off the slight powder residue with water.  The fan is lubricated and turns freely and for some time with a manual spin of the blades, and generates quite a torrent of air when connected to power.  I've carefully inspected the hoses for cracks and leaks.  I've operated it with the fan removed from the chimney, so the system is just the fan, venturri, hoses, and the switch.  It still doesn't make.

    Finally, I put the switch's negative pressure hose into a glass of water, and applied tiny pressure to the positive hose with a syringe and saw bubbles in the water. That tells me the switch diaphragm is punctured and leaking air.

    I have a simple manometer made of a loop of water-filled Tygon tubing attached to a vertical ruled board that I used several years ago to adjust the propane tank gas regulator.  That's the original definition of water column inches, and worked fine for measurements in the 11" WC range.  It's probably too crude for making accurate measurements in the 0.25" - 0.35" range, so I may have to buy an electric manometer to set it accurately.

    I'm wondering why there are two numbers on the original switch -- 82 and 66 Pascals.  Could this be to account for switch hysteresis, as in make contact as the pressure goes above 82 Pa, and break contact when it falls below 66 Pa?  Hysteresis would avoid switch chatter at the critical pressure.  Or could it be that 82/66 merely represents the accuracy tolerance promised by the manufacturer?

    I don't think there's anything magical about this switch just because it's European. It's just a 2-port differential switch.

    Thanks for your thoughts on this.

    Mark E.

    Pátzcuaro, México
  • unclejohn
    unclejohn Member Posts: 1,751
    Have you tried other manufacture's of boilers or furnaces and see if any of there switches match your needs or get close enough.