Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards
No hot water at all usually means power, gas or ignition. Not enough hot water usually means a failed lower element, sediment, or a tank too small for demand. Lukewarm water that never gets hot points at a thermostat, an element or a broken dip tube.
Two things are never a repair: a tank leaking from the shell, and a tripping temperature and pressure relief valve. The first means replacement; the second is a safety device reporting a problem, not a nuisance to be capped.
Start by naming the symptom
| Symptom | Electric | Gas |
|---|---|---|
| No hot water at all | Breaker, high-limit reset, both elements or thermostats | Pilot or igniter, thermocouple or flame sensor, gas valve, gas supply |
| Runs out quickly | Lower element failed | Sediment, undersized tank, dip tube |
| Lukewarm, never hot | Thermostat setting or upper element | Thermostat setting, burner fouling |
| Slow recovery | Element scaling | Sediment insulating the tank bottom |
| Rumbling or popping | Rare | Sediment, common in hard water |
| Water around the base | Could be the tank, TPR discharge or a fitting | Same, plus condensation on a cold refill |
What an owner can safely check
- The breaker or the gas supply. Confirm other gas appliances work; reset a tripped breaker once.
- The thermostat setting, against the setting the manufacturer recommends for your model.
- The high-limit reset on an electric heater, the button behind the upper access panel. If it trips again, stop; something is causing it.
- Recent demand. A long guest weekend is not a fault.
- The age, from the serial number, because it frames whether a repair is worth doing.
Beyond that, an electric water heater’s elements sit on a 240 volt circuit and a gas unit involves combustion. Both are service calls, and our contractor checklist covers what to verify before booking one.
A temperature and pressure relief valve that discharges is doing its job. It usually means excessive pressure or temperature in the system, sometimes from thermal expansion in a closed plumbing system with no expansion tank. The valve must never be plugged, and its discharge pipe must run to a safe location. Treat a discharging TPR valve as a fault to be diagnosed, not a part to be replaced and forgotten.
Sediment, the quiet cause
Minerals settle to the bottom of a storage tank. On a gas heater that layer sits between the burner and the water, so recovery slows and the tank rumbles as steam bubbles form beneath it. On an electric heater it buries the lower element.
Periodic flushing is the maintenance that addresses it, and it matters more in hard water areas. Where sediment has been left for years, flushing sometimes reveals a leak it was effectively plugging, which is an argument for doing it regularly rather than once at year ten.
Tankless units fail differently
- Minimum flow rate. A tankless heater needs a minimum flow to fire, so a trickling tap may produce cold water by design.
- Scale. Heat exchangers scale in hard water, and descaling is routine maintenance rather than a repair.
- Gas supply sizing. Tankless units have high input rates; an undersized gas line shows up as failure under load, not at idle.
- Error codes. Unlike tanks, these units report faults; the code is the starting point.
When it is time to replace
A tank leaking from the shell is finished; the steel has corroded through. Repeated element or thermostat failures on an old unit, or a gas control valve failure on a heater near the end of its life, usually push the same way.
Our water heater replacement guide covers sizing on first hour rating, fuel choice, and the federal efficiency rules, including the storage standards arriving in 2029. Shipment trends are in our shipments report.
Frequently asked questions
Why is my water heater not heating?
If there is no hot water at all, suspect power or gas supply: a tripped breaker or high-limit reset on electric, or a pilot, igniter, thermocouple or gas valve fault on gas. If water runs out quickly, suspect a failed lower element on electric or sediment on gas.
Why does my hot water run out so fast?
On an electric heater, a failed lower element heats only the top of the tank, so the supply ends sooner than it used to. On a gas heater, sediment on the tank bottom slows recovery. Undersized capacity for changed household demand produces the same complaint without any fault.
Is a leaking water heater dangerous?
Water from the tank shell means corrosion has gone through and the heater needs replacing, not repairing. Water from the temperature and pressure relief valve is different: the valve is discharging for a reason, often excess pressure or temperature, and that cause needs diagnosing. Never plug a relief valve.
Can I fix a water heater myself?
You can check the breaker, the gas supply, the thermostat setting and the high-limit reset. Replacing elements, thermostats, gas valves or thermocouples involves a 240 volt circuit or a combustion appliance, and both are service work in most jurisdictions.
Methodology and limitations
This page describes failure modes of residential storage and tankless water heaters in general terms. The manufacturer’s instructions govern settings, parts and clearances for a specific model.
- No federal source measures water heater failure rates or repair prices, and we publish neither.
- Recommended temperature settings vary by model and by household circumstances.
- Nothing here is a substitute for a qualified technician.
Sources
- Code of Federal Regulations, 10 CFR 430.32(d), water heater efficiency standards.
The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.
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