Burn marks are a BIG warning sign. If there are burn marks on the bottom of your water heater, you could usually have one, if not more, possible problems. (Burn marks are usually only on gas or propane water heaters)
Issue: Unit is not venting properly
Improper water heater venting causing burn marks is caused from backdrafting. This is a serious problem! Immediate attention and repair is most likely needed being it means you’ve got natural gas and exhaust fumes that aren’t exiting your property. Instead, the poisonous gases are staying in the house. Not a good situation.
If venting is your issue, you’ll need to call a plumber to get the vent fixed. It doesn’t immediately call for a replacement. But if the vent isn’t fixed, your water heater WILL fail (so will each water heater you install. Fix the ventilation)
Issue: Flue is damaged
Burn marks can also mean the flue pipes are blocked or damaged. This is also a potentially unsafe situation, so that water heater will need to be replaced – and soon.
You’re going to need a water heater replacement. Get a plumber onsite as soon as possible.
Other Possible Causes:
- Poor draft/draft problems
- Flue pipe height or location at roof
- Rust/scale covering burners
- Hole in heat exchanger