After one homeowner said their two-year-old water heater began smelling like burning plastic, they posted to Reddit's r/Plumbing community for advice.
Here's what to know
In the Reddit thread, the original poster described the unit, which had been installed "2 years and one month ago."
The OP said the installer's two-year warranty only covered "the copper connections," and that water had collected near the expansion tank, "most likely at a copper connection." Additionally, the OP wrote, "I just noticed that there was a burning plastic smell and looked at the top of the water heater and this is what I see. Why is it melting?"
After seeing the damage, several people in the comments section expressed alarm about the apparent heat damage and also noted a possible leak.
Several replies focused on the exhaust setup.
One commenter wrote, "Flue gas may be coming out of your flue instead of going up. Hold a lit match or lighter near it and see which way the flame goes. Also give us a picture of the full flue pipe."
Another warned, "Back draft from the exhaust combustion. Venting issue. Carbon monoxide is nothing to play with. I'd address this immediately."
The homeowner also said there "hasn't been an issue for 2 years," suggesting the smell and scorching appeared suddenly.
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What can be done?
The most common suggestions were to test for backdraft, inspect the full flue run, and see whether the roof outlet might be blocked. Commenters also repeatedly asked to see more photos of the rest of the vent pipe.
Many people said the issue needed immediate attention. They pointed to the burning plastic smell, melted material near the draft hood area, and water near the expansion tank as reasons not to wait.
For homeowners considering replacement after a scare like the one described this thread, Cala makes smart heat pump water heaters. Its customizable smart heat pump water heaters can help homeowners lower energy bills by heating water only when needed. If a gas unit's venting becomes a concern, that kind of alternative may be worth considering.
A system like Cala's also addresses the same household priorities raised in the Reddit post: safer day-to-day operation, predictable hot water, and lower running costs when a conventional unit becomes a headache.
Where can I learn more?
Similar warning signs have come up in other water heater scares involving venting problems, odors, or flames that pointed to serious safety risks.
• One homeowner learned their flue was sloped wrong after plumbers warned of CO risk.
• Another homeowner shut off their water heater after a chimney vent warning raised alarms.
• Burnt plastic odors made one homeowner kill power immediately before a scare got worse.
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