Why is my hot water heater not working?
No hot water from a gas water heater is almost always a pilot light out or a failed thermocouple ($150 – $300 to repair). On an electric water heater, it's usually a tripped breaker or burned-out heating element ($200 – $500). Either way, the fix is cheap if the unit is under 10 years old — but past that, a repair is often the first sign a replacement is coming.
Check the unit's age first. The nameplate on the side lists the manufacture date — a water heater pushing 12–15 years that just lost hot water is often telling you it's time to replace it, not repair it.
Most likely causes
| Cause | How to tell | The fix | Typical cost |
|---|---|---|---|
| Gas: pilot light is out | No hot water; pilot light window on the tank shows no flame; happened after the gas was turned off or a strong draft | Relight the pilot following the label on the front of the water heater — most have a piezo igniter button and step-by-step instructions printed on the unit itself. If the pilot won't stay lit, the thermocouple is likely the issue | $0 to relight; $150 – $250 if thermocouple replacement needed |
| Gas: failed thermocouple | Pilot lights but goes out within 30–60 seconds every time you release the pilot button; no hot water as a result | The thermocouple is a safety sensor that detects pilot flame — when it fails, it shuts off the gas supply as a safety measure. Replacement is a straightforward plumber job | $150 – $300 |
| Electric: tripped breaker | No hot water on an electric tank; water heater breaker is tripped in the panel; happened after a thunderstorm or power surge | Reset the breaker once. If it trips again immediately or within an hour, the heating element has failed and is causing the short — call a plumber | $0 to reset; $200 – $500 if element replacement needed |
| Electric: burned-out heating element | Water is lukewarm but never fully hot (bottom element), or runs hot for only a few minutes then cold (top element); breaker is fine | Replace the failed heating element — most 40–50 gallon tanks have two. A plumber drains the tank partially and swaps the element | $200 – $500 |
| Thermostat set too low or failed | Water is consistently lukewarm, never scalding; happened gradually rather than suddenly | Check the thermostat setting on the tank (120°F is standard, 110–115°F causes lukewarm complaints). If adjusting the dial doesn't help within a few hours, the thermostat has failed | $150 – $350 |
| Sediment buildup — reduced capacity | Hot water runs out much faster than it used to; rumbling or popping sounds from the tank; unit is 8+ years old | Flush the tank to remove sediment (annual maintenance that most homeowners skip). Heavy buildup in an older tank may be past the point of flushing — replacement is often the better call at this stage | $0 DIY flush; $150 – $250 professional flush; $1,200 – $3,500 replacement if severely scaled |
Try this first (before you pay anyone)
- For a gas water heater: look for the pilot light window on the unit and check whether the flame is visible. If it's out, follow the relighting instructions printed on the tank label — this takes 5 minutes and costs nothing.
- For an electric water heater: check the breaker in your electrical panel. Water heaters use a dedicated double-pole breaker that trips to the middle position — flip it fully off, then back to ON.
- Check the age of the unit from the data plate or serial number. If it's 10 years or older and you're seeing the first failure, budget for replacement even if you repair it now — the next failure is usually close behind.
- On a gas water heater: if the pilot stays lit but no hot water is coming out and you smell gas at any point — leave the house immediately and call your gas utility. Gas leaks near a water heater are an emergency.
Call a pro when…
- The pilot won't stay lit after relighting — thermocouple failure needs a plumber, not a DIY fix involving the gas valve
- You smell gas near the water heater at any time — this is an emergency. Leave the building and call your gas utility before calling a plumber
- The electric water heater's breaker trips repeatedly — the heating element is shorting and repeated resets can create a fire hazard
- You see water pooling around the base of the tank — a leaking tank usually means replacement, not repair (see water-heater-leaking)
Repair or replace?
Water heaters last 8–12 years for tank models (12–20 years for tankless). If the unit is under 8 years old and facing a single part failure (thermocouple, element, thermostat), repair is an easy yes — the repair cost is $150–$500, far less than a new unit at $1,200–$3,500 installed. At 10–12 years with a first failure, get a replacement quote alongside the repair quote. Past 12 years, a repair usually just delays an inevitable replacement by 1–2 years — and a new unit often pays back in energy savings within 3–4 years.
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Related questions
How long does it take to get hot water back after a repair?
After a pilot relight or thermocouple replacement, a gas water heater takes 30–45 minutes to reheat a full tank. After an electric element replacement, expect 1–2 hours to reach full temperature. Running the hot water tap briefly after a repair speeds up the wait — cold water is purged from the pipes faster.
Why does my hot water run out so fast?
Fast hot water depletion is usually a failed lower heating element (on electric tanks) or heavy sediment buildup coating the bottom of the tank — sediment insulates the water from the burner and cuts effective capacity dramatically. On tanks under 8 years, a flush and lower element replacement typically restores full capacity.
What temperature should I set my hot water heater?
120°F is the standard — hot enough to kill legionella bacteria (which grows between 77–113°F) while still being safe at the tap. Homes with immunocompromised occupants or elderly residents can set to 130°F, but use a mixing valve at fixtures to prevent scalding.
Is a gas or electric water heater cheaper to repair?
Repairs are comparable in cost ($150–$500 for the most common failures on either type). Gas units have more parts that can fail (thermocouple, gas valve, pilot assembly) but those parts are inexpensive. Electric units have fewer failure points but a heating element replacement requires draining part of the tank. Long-term operating costs favor gas in most markets.