Water Heater Made a Loud Bang: What to Do
On this page (5 sections)
The Short Answer: A single loud bang or “whoomp” right as a gas water heater’s burner lights usually means delayed ignition: gas built up before it lit. Turn the control to OFF and do not relight it until a technician has checked the burner, pilot, and gas supply. Repeated popping while the burner is already running is more often sediment, and a bang when a faucet closes is water hammer.
Which kind of bang was it?
| When it happened | Likely cause | What to do |
|---|---|---|
| The moment the burner lit, sometimes with a puff of air or a rattled cover | Delayed ignition | Turn the control to OFF; do not relight |
| Bang plus a gas smell | Gas leak or a large amount of unburned gas | Leave and call from outside |
| Repeated popping or rumbling while the burner is running | Sediment on the tank bottom | Schedule service; see water heater sounds like rocks |
| Bang in the pipes when a faucet, washer, or dishwasher shuts off | Water hammer | A plumbing issue; see water heater clunking sound |
| Bang soon after a new heater or gas work | Air in the gas line or an installation issue | Turn it off and call the installer |
Why delayed ignition happens
Normally the main burner lights smoothly from the pilot or igniter within a moment of the gas valve opening. If that ignition is late, gas spreads through the combustion chamber and then lights all at once. Common reasons include a small or misdirected pilot flame, a dirty or misaligned burner, a weak or failing igniter on electronic-ignition models, incorrect gas pressure, a blocked flammable-vapor (FVIR) air intake, or a burner that is damp from condensation or a leak. A hard bang can unseat the combustion chamber cover or damage the burner, so the heater should be inspected even if it seems to run normally afterward.
What you can check safely
- Turn the gas control to OFF using the instructions on the heater’s label.
- Look through the sight glass (without removing covers) for soot, a crooked inner door, or signs of water in the burner area.
- Look at the draft hood and vent for soot or a pipe knocked loose.
- Check for lint and dust around the bottom air intake, and keep the area clear.
- Note when it happened and whether there were earlier, quieter “whoomps” you had ignored.
Do not keep relighting the heater to see if it happens again, and do not loosen any gas fittings to “bleed air.”
What the technician will check
A qualified gas technician inspects and cleans the pilot and burner, checks that the pilot flame is the right size and reaches the burner, measures gas supply and manifold pressure against the rating plate, checks the igniter or ignition sequence on electronic models, and inspects the venting and combustion chamber for damage. After a strong bang they also check the inner door seal and FVIR components, since a damaged seal affects safe operation. Most delayed-ignition causes are repaired with cleaning, adjustment, or a part such as a pilot assembly or gas control; see replace a water heater pilot assembly.
Frequently Asked Questions
Q: Can a water heater explode from a bang like this? A: A delayed-ignition bang is a small combustion event in the burner chamber, not a tank explosion. It can still damage parts and roll flame out of the chamber, which is why the heater should stay off until inspected. A tank explosion is a different scenario involving a failed relief valve and runaway temperature, which is why the relief valve must never be capped.
Q: My electric water heater banged. Is that delayed ignition? A: No, electric heaters have no burner. A bang from an electric heater is usually water hammer in the pipes or sediment. A loud crack with a burning smell or a tripped breaker suggests an electrical fault; leave the breaker off and call for service.
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.
Editorial standards and corrections · Prepare a useful service request