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
- There could be something lodged in the vent
- There could be something obstructing the termination
- Snow could be covering the outlet
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- Remove it
- Remove it
- Vent may need to be extended or rerouted above the snow line.
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| Poor combustion |
- Check that the appropriate amount of combustion air is being supplied to the room or appliance(s)
- Verify that the appliance combustion air filter is not dirty
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Back Draft |
- 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.
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Bad Spill Switch |
- Check that the spill switch works properly
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| Overly cold vent pipe |
- Insulate vent
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Improper Design |
- Verify that vent design is in accordance with the NFGC. If design is incorrect, it must be corrected.
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Mechanical room is negatively pressurized
- 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.
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- 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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