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  • What is the correct way to set the bypass on a FDO thermostat?

  • guest

    May 14, 2015 at 12:00 am

    What is the correct way to set the bypass on a FDO thermostat

  • ectofix

    May 15, 2015 at 5:00 am

    That’s a good question to ask.  I’ve often encountered temperature-related service calls on those thermostats where I found they weren’t set up properly during installation (i.e., replaced by someone not knowing how).


    MOST manufacturers of ovens & griddles employing those thermostats provide a step-by-step procedure in their service manuals.  You might want to check that out.  Otherwise, here’s MY step-by-step procedure:


    Assuming the thermostat is GOOD:

    • Set it to an appropriately high set-point.  350° sounds good.  Let it get happy there.  Monitor the temperature with a quality digital thermometer to be sure.  If the thermostat is off by more than 50°, manufacturers will tell you to replace it.

    -NOTE: If you’re working on an existing thermostat and was told it’s getting too hot, don’t assume it’s a bad thermostat yet.  Try adjusting the bypass DOWN first.  Somebody may have set it up wrong during replacement.

    • Once the thermostat has satisfied and throttled down, Turn its setting DOWN to something like 250°…WELL below set-point.  At this point, thermostat should only be passing gas through its bypass flame internal port.
    • Inspect the flame.  It should around1/8″ high.  All burner ports should be participants throughout the perimeter of the of the burner and should show established but small flames each.  No flame fluttering or “walking” allowed.
    • If the flame is ABOVE 1/8″, take a slot screwdriver and adjust the “B” screw (bypass) on the thermostat body IN – slowly and incrementally clockwise to gradually reduce gas flow to the burner.
    • If the flame is BELOW 1/8″ or trying to go out, adjust it OUT – slowly and incrementally counter-clockwise.
    • If you think you got it, check your work.  Briefly throttle the thermostat way above actual oven temperature to gain a full flame again, then crank it back down below actual oven temperature.


    Did the bypass flame maintain your setting?  Very likely.  If not, then make further adjustments accordingly.


    Final checks:

    • Let the thermostat ride at a set-point lower than actual oven temp.  The temp you’re reading on the digital thermometer should drop.  It will do so  s-l-o-w-l-y, but it should drop.
    • Obviously when the thermostat is at bypass flame,the oven temperature should NEVER continue to rise.
    • After all this is done, THEN check and adjust calibration of the thermostat.

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