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What causes scorched burn marks near the bottom of a gas water heater?
Thursday, June 21, 2018
The burn marks are caused by flames shooting out of the access opening to the burner compartment. It usually happens only briefly and intermittently, but can be a fire hazard and will eventually damage the internal components of the water heater.
The defect is called “flame rollout,” or sometimes referred to as “flashback,” and here’s a list of possible causes:
- Delayed ignition after gas valve opens
- Over-firing of the burner
- Corrosion damage or corrosion debris in burner compartment
- Obstructed flue or downdraft
- Negative air pressure in room
- Lack of combustion supply air
It can be difficult to determine if flame rollout is an ongoing problem or a previous event, although particularly dark and large marks would tend to indicate a long-term issue. Either way, we recommend immediate service by a plumber or gas appliance professional.
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