Can a Water Heater Explode? Warning Signs and Fixes

Reviewed by Alejandro Morales, Co-Owner & FL Certified Plumbing Contractor (FL license CFC1431159)Updated Oct 12, 2026

Why does a water heater explode in the first place?

A tank heater holds hot water under pressure. Heat makes the water expand, and if the heater keeps heating with nowhere for pressure to go, the tank can rupture. Every tank is built with a T&P valve to prevent that. It opens and lets hot water out through a pipe near the floor.

Problems start when the valve is stuck, corroded, capped off by someone, or removed. A thermostat stuck on, or a failed gas control valve, keeps the burner or element running past the safe point. Heavy sediment can also overheat the bottom of the tank. In Tampa, City of Tampa water averages 10.8 grains per gallon of hardness (very hard), so scale and sediment build up quickly in tanks that are never flushed.

Safety note: If you smell gas (rotten eggs) near a gas heater, leave the house right away and call the gas utility or 911 from outside.

What are the warning signs a water heater is in trouble?

What should I do right now?

If you smell gas, do not touch switches or lights. Walk out, then call the gas utility or 911. For anything else, turn the heater off. On an electric unit, switch off its breaker. On a gas unit, turn the gas control to off. Close the cold water supply valve on top of the tank if the leak is active. Then call us.

Do not cap or plug the relief valve pipe, and do not stand close to a tank that is hissing or shaking.

How do I keep a water heater from becoming dangerous?

• Test the T&P valve. Lift the lever briefly with a bucket or the discharge pipe in place. Water should flow and stop when you let go. If it drips afterward or does nothing, it needs replacing.
• Keep the temperature near 120 F. See our guide on the water heater temperature setting.
• Flush the tank every year. Our water heater flush is $89 (tank or tankless) and includes a whole-house plumbing inspection. It is a standing price, not a first-visit offer.
• Add an expansion tank where code requires one. It gives thermal expansion somewhere to go.

An old tank that leaks or rusts is better replaced than repaired. If yours is near the end of its life, look at water heater installation. For a failed valve, thermostat or element, see water heater repair.

What does Home Therapist do?

Home Therapist Cooling, Heating and Plumbing is open 24/7 across Hillsborough, Pinellas and Pasco counties. We give FREE estimates and a FREE diagnosis on every visit, at any hour, with no service call or after-hours fee. You approve a written quote before any repair begins. Call or text (813) 343-2212. More on our plumbing services.

Related: What a Water Heater Expansion Tank Does | Why Is My Water Heater Leaking?

Frequently Asked Questions

Can a water heater explode if it is turned off?

It is very unlikely. A heater that is off is not adding heat, so pressure does not build. The danger comes from a unit that keeps heating with a failed thermostat, a bad gas control or a blocked relief valve. Turning it off is the right first step.

Is it normal for the relief valve to drip?

Not usually. A steady drip or steam means high pressure, high temperature or a worn valve. Do not cap it. Turn the heater off and have it checked, because the valve is the safety device that prevents a rupture.

Do tankless water heaters explode?

Tankless units do not store a tank of hot water, so the risk is much lower. They can still have gas, venting or scale problems. A yearly descale and flush keeps them running safely, and it is also $89.

Why does my water heater make popping noises?

Popping or rumbling is usually sediment on the bottom of the tank. Water trapped under the layer boils and bursts through. It wastes energy and overheats the tank, so a flush is the fix. Hard Tampa water makes it common.

How old is too old for a tank water heater?

Many tanks wear out in roughly 8 to 12 years, and hard water can shorten that. Rust, leaks at the base and rusty hot water point to a failing tank. We inspect it for free and tell you whether repair or replacement makes sense.

Should I replace the T&P valve myself?

We recommend a plumber do it. The tank must be depressurized, the discharge pipe set up correctly and the fittings sealed. A mistake can leave you with no protection or a leak. Our diagnosis is FREE at any hour.