Water Heater Control Box Leaking Gas: What to Do
On this page (6 sections)
The Short Answer: If you smell gas at your water heater’s control box (the gas control valve on a tank, or the gas valve inside a tankless unit), treat it as a gas leak. Leave the building without operating switches or the heater, and call the gas utility or 911 from outside. Don’t look for or tighten the leak yourself; a licensed gas technician will.
Right now
- Get everyone, including pets, out of the building.
- Leave doors open behind you if you can do it without delay.
- From outside, or from a neighbor’s home, call your gas utility’s emergency number or 911.
- Stay out until the utility or fire department says it is safe.
Gas utilities treat leak reports as emergencies and can shut off the supply at the meter. Pacific Gas & Electric’s gas leak guidance (opens in a new tab) is a good example of what utilities ask customers to do.
What not to do
- Don’t tighten, loosen, or tap any fittings, the control valve, or the flexible gas connector.
- Don’t spray soapy water on fittings to look for bubbles while the room smells of gas.
- Don’t try to relight the pilot or reset the heater.
- Don’t turn the gas control knob back and forth, and don’t operate electrical switches near the heater.
Is it really gas?
Natural gas and propane have an added odorant that smells like rotten eggs or sulfur, and you should treat that smell in the air as a leak. A few other smells get confused with it:
| Smell | Where | What it usually is |
|---|---|---|
| Rotten eggs in the air around the heater | Room air | Gas leak: leave and call |
| Rotten eggs only from the hot tap water | Faucets | Bacteria reacting with the tank’s anode, not a gas leak; see the water heater smells hub |
| Brief whiff right when the burner lights, then gone | At ignition | Possibly delayed ignition or a small amount of unburned gas; still needs checking; see smell gas when water heater turns on |
| Odor after a new heater was installed | Around new connections | A connection may not be tight; see gas smell after water heater replacement |
If you can’t tell, treat it as gas.
What the gas technician will check
Once the area is safe, the utility or a licensed gas technician will pressure-test and leak-check the supply line, the connector, the fittings at the control, and the control itself with an approved method or an electronic detector. They check the control’s regulator and vent. A gas control that leaks through its body or regulator has to be replaced as a unit with one that matches the heater model and gas type. Gas controls are not repaired internally. After any repair, they confirm the connections are tight, relight the heater, and check that it is burning and venting correctly.
Repair or replace
A leaking connector or fitting is a small repair. A leaking gas control is a part replacement, though on older tanks it can be worth comparing the cost against a new heater, especially if replacement controls for that model are hard to get. The technician can tell you which applies. Knowing your heater’s age helps with that decision.
Frequently Asked Questions
Q: Can I just turn off the gas valve to the water heater and wait? A: If the smell is strong, leave instead of going near the heater. Closing a valve might not stop a leak that is upstream of it, and the risk comes from gas already in the room.
Q: My carbon monoxide alarm went off as well. Is that the same problem? A: Not necessarily. CO comes from incomplete combustion or blocked venting, not from unburned gas. Either way, get outside and call 911 or the utility. See hot water heater carbon monoxide leaks.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
- CPSC: carbon monoxide fact sheet (opens in a new tab)Carbon monoxide hazards and emergency response.
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