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F.A.I.S. Boiler occasional no-start

g92065 Member Posts: 4
Hello All! I am a homeowner who purchased a house with a propane-fired boiler, F.A.I.S. brand, made in Italy, vintage about 1998. It is now obsolete. I was lucky enough to buy some spare parts about 10 years ago, and I swap them in occasionally when there is a problem. Typically, as the main bearing in the fan wears out, the fan speed is insufficient to get the differential pressure required to allow the gas valve to open. You can hear the bearing as it gets rougher...it's noisy. I used to just change the bearing, and all would be good for another 2-3 years or so. Since I have a spare fan, it is always a quick swap out.

Recently, the boiler fan runs and runs, and the gas valve never opens. This typically occurs in the warm daytime, after the boiler has been running a bit, and the demand asks for another heat cycle. I changed the fan again, no joy. I swapped out the differential pressure switch with my spare, and it's still doing the same thing. The silicone hoses going from the fan to the differential pressure switch appear good.

If I cycle the switch off and on, it goes through its normal startup procedure and fires right up, every time.

I could make a manometer to see what the differential pressure is, but I don't know what it's supposed to be.

Any ideas???

Boiler is part of a hydronic floor system, with a heat exchanger for domestic supply.


San Diego


  • Jamie Hall
    Jamie Hall Member Posts: 23,280
    The fan may be running, but is it getting up to full speed? And is the intake and exhaust free and unobstructed?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • g92065
    g92065 Member Posts: 4
    This fan is one speed, as far as I know. Intake and exhaust are coaxial, and free.

  • g92065
    g92065 Member Posts: 4
    Am I getting the squirrel cage in the housing correctly? I try to center it...should it favor one side more than the other?
  • Alan (California Radiant) Forbes
    I'm amazed that your FAIS boiler is still running; good for you. There were three of them on my route and I've replaced them all long ago.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • kcopp
    kcopp Member Posts: 4,432
    Is the gas valve done?
    I am also surprised hat is still working... I installed about 3-4 of those years ago. they had a small indirect that went w/ them that was great.
    The boiler was sold in the UK under the Ravenheat brand name.
    HVACNUT Member Posts: 5,833
    10m bar is what's needed to open the pressure switch. Convert that to inches of mercury for your manometer. 
    Is there a wiring diagram you could post? I'm wondering why the pressure switch is N.C. What's on the N.O. contact?
  • g92065
    g92065 Member Posts: 4
    What does it mean "Is the gas valve done?" I can hear the gas valve open when it does work. The problem is that when it doesn't work, I only know by the lack of hot water...I'm never around to see/listen on a non-start. If I recycle the switch, it starts right up.

    So, what I did today was swap in my spare ignitor. Interesting thing is that right on the ignitior, it states, "This device can malfunction if it gets wet. Never try to use a device that has been wet--replace it."

    I do believe it got wet about 7 or 8 years ago, when the pressure dampener behind it sprang a leak above it. I took that dampener out of service and put another one in the primary loop.

    Alan Forbes, you might know my friend Bill Turner of Lintelle Engineering in Scotts Valley. He fixed my spare circuit card to use a replaceable relay. The box holding my spare has his company name on it.