Water Heater Not Producing Hot Water: Diagnosis Guide
No hot water doesn't always mean a failed water heater. Work through this diagnostic before scheduling a service call — the fix is often free or under $50.
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Gas vs electric: different first steps
Gas water heater — check the pilot light first. Locate the viewing window near the bottom of the tank. If you see no flame, the pilot has gone out. Relight it following the instructions on the unit label (usually: turn the knob to Pilot, hold it down, press the igniter, hold 30 seconds, release, turn to desired temperature). If the pilot won't stay lit, the thermocouple has likely failed — a $15–30 part that a plumber replaces in 30 minutes ($100–150 total).
Electric water heater — check the circuit breaker first. Electric water heaters draw significant current and trip breakers during a power surge or if the element shorts. Reset the breaker. If it trips again immediately, you have a shorted heating element — not a breaker problem.
Systematic diagnosis by symptom
No hot water at all (electric)
1. Reset the breaker. 2. If power is restored but still no hot water, press the red reset button on the high-limit thermostat (located behind the upper access panel on the front of the tank). 3. If that doesn't work, test the upper heating element — if it's shorted, it takes out the entire heater. Element replacement: $15–30 for the part, $100–200 for a plumber to install it.
Hot water runs out in 20–30 minutes
Classic sediment symptom. Sediment that settles at the tank bottom insulates the lower heating element, reducing efficiency by 30–50%. Flush the tank: attach a hose to the drain valve, run it to a floor drain, open it for 5–10 minutes until the water runs clear. If flushing doesn't improve it, the lower element may need replacement.
Lukewarm water, not hot
Check the thermostat setting (the dial behind the access panel, or on the gas valve). Should be set to 120°F for most households. If the thermostat is set correctly but water is still lukewarm, one of two elements has failed (electric) or the dip tube has broken (allows cold inlet water to mix with hot at the top of the tank).
Hot water smells like sulfur/rotten eggs
The anode rod is reacting with sulfur bacteria in the water. Most common with well water or in areas with high-sulfur municipal water. Replace the magnesium anode rod with an aluminum/zinc anode rod — zinc inhibits the reaction. Anode rod replacement guide here.
Water heater leaking from the top
Usually a loose inlet/outlet connection or a faulty T&P relief valve (temperature-pressure relief valve). The T&P valve is a safety device — if it's leaking, it may be doing its job (pressure too high) or it may need replacement ($15–30 part). Do not cap or plug a T&P valve. If pressure is the cause, check if you need an expansion tank.
Water heater leaking from the bottom
Usually the drain valve or, worse, a crack at the tank base. A cracked tank cannot be repaired — the unit needs replacement. If you see pooling water at the base with no identifiable source at a fitting, assume tank failure. Shut the unit off and call a plumber.
Repair vs replace decision
Use this framework before paying for any repair:
- Under 8 years old: Repair is almost always worth it. Heating elements, thermostats, and thermocouples are cheap. The tank itself is fine.
- 8–12 years old: Depends on the repair cost. A $150 element replacement is worth it. A $400+ repair on a 12-year-old tank is borderline — get a quote on replacement at the same time.
- Over 12 years old: Lean toward replacement. You'll likely face another repair within 2–3 years, and modern units are significantly more efficient. The exception: a high-quality tank (Bradford White, Rheem) in good condition with minor issues.
- Leaking tank: Replace, always. There is no repair for a leaking tank.
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