TL;DR
A vent spill switch is a thermal safety switch mounted at the draft hood or diverter of a gas water heater or furnace that shuts off the gas valve when hot flue gases roll out of the hood instead of rising up the vent. Spillage happens with blocked chimneys, backdrafting from house depressurization, or failed draft, all of which dump combustion products and carbon monoxide indoors.
What it means
A vent spill switch is a thermal safety switch mounted at the draft hood or diverter of a gas water heater or furnace that shuts off the gas valve when hot flue gases roll out of the hood instead of rising up the vent. Spillage happens with blocked chimneys, backdrafting from house depressurization, or failed draft, all of which dump combustion products and carbon monoxide indoors. Some switches reset manually and some automatically, and a unit that keeps tripping is diagnostic gold: the venting has a real problem, and bypassing the switch instead of fixing it is how CO deaths happen.
Where it sits in the glossary
Vent spill switch is part of the Trade jargon group inside the ProFix Directory glossary. Browse every term in this category from the glossary index.
Why Ohio homeowners should know it
This is a term Ohio homeowners encounter when reading contractor quotes, hiring paperwork, or inspection reports. Understanding it well enough to ask one good follow-up question is usually all the protection a homeowner needs.
ProFix Directory keeps definitions short on the index page and saves the longer context — Ohio-specific rules, where the term comes from, and which ProFix tools touch it — for these per-term pages so the term is easy to cite and easy to share.
ProFix tools that touch this term
See also
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