Possible causes of spill switch issues

Possible causes of spill switch issues

What is a spill switch?

A spill switch is a device that is used on venting systems that is designed to stop the combustion process if the exhaust gasses are spilling into the mechanical room.  For category I venting appliances, the spill switches are often mounted on the lower lip of a barometric damper or on a draft hood.  Exhaust gasses are hot, so when they spill onto the spill switch, the device will open a wired contact, disrupting the operation of the appliance.

Possible causes of spill switch issues


Causes
Solutions
Blockage of the exhaust vent
  1. There could be something lodged in the vent
  2. There could be something obstructing the termination
  3. Snow could be covering the outlet


  1. Remove it
  2. Remove it
  3. Vent may need to be extended or rerouted above the snow line.
Poor combustion
  1. Check that the appropriate amount of combustion air is being supplied to the room or appliance(s)
  2. Verify that the appliance combustion air filter is not dirty
Back Draft

  1. If you find that you have a backdraft due to a windy location, you may need to obstruct the wind or provide a mechanical means of inducing draft.
Bad Spill Switch

  1. Check that the spill switch works properly
Overly cold vent pipe
  1. Insulate vent
Improper Design

  1. Verify that vent design is in accordance with the NFGC.  If design is incorrect, it must be corrected.
Mechanical room is negatively pressurized
  1. Verify if the room is negatively pressurized.  This can be done with a testing device or by feeling the flow of the air at a partially opened door. 

  1.  If negatively pressurized, find out why and rectify the problem.  You may need to properly seal sources of negative pressure.  This may require more detailed investigating.



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