Most water heater problems fall into recognizable symptom patterns. This page maps the symptom to likely causes and links to dedicated fix guides. For brand-specific error codes on tankless and combi units, see the brand error code hubs: Rinnai, Navien, Rheem.
Symptom directory
| Symptom | Most common cause | Fix guide |
|---|---|---|
| Water around the base | Tank shell crack OR drain valve drip | Leaking |
| No hot water at all | Gas: pilot/thermocouple. Electric: breaker/element/thermostat | No hot water |
| Hot water runs out in 5-10 min | Broken dip tube, sediment, failed lower element | Runs out fast |
| Lukewarm water (never gets hot) | Lower element/thermostat, dip tube | No hot water — lukewarm |
| Popping or rumbling noise | Sediment cooking on tank bottom | Popping noise |
| Rotten egg / sulfur smell | Sulfate bacteria + magnesium anode | Sulfur smell |
| Rusty / brown hot water | Anode rod consumed, tank corroding | Anode rod |
| T&P valve drips | Thermal expansion (no expansion tank) OR failed valve | T&P valve |
| Water hammer / banging pipes | Missing or failed expansion tank | Expansion tank |
| Pilot won't stay lit (gas) | Thermocouple, on Bradford White also intake filter | BW troubleshooting |
| Burner cycling (gas) | Undersized gas line, thermostat issue | Brand-specific |
| Tankless error code | Numeric code — look up specific code | Brand error code hubs |
| Breaker trips (electric) | Shorted element, water in element jacket | Element |
Emergency situations — stop here
If you're seeing any of these, take immediate action BEFORE troubleshooting:
- Water actively pooling/flooding: shut off cold-water supply at the heater inlet. Shut off gas or breaker. Drain the tank to a hose if needed
- T&P valve in continuous heavy discharge: shut off cold-water supply immediately. Tank may be overheating. Allow to cool 30 minutes before investigating
- Gas smell near the unit: shut off the gas supply valve (typically a yellow handle on the gas line, perpendicular = closed). Open windows. Call the gas utility from outside the house
- Sparks or burning smell from electric panel: shut off the main breaker. Call an electrician
Diagnose before you call
For non-emergency problems, narrow it down yourself first — saves a service call:
- What type of unit? Gas tank, electric tank, gas tankless, electric tankless, heat pump, combi boiler. Each has different failure modes
- How old? Decode the serial number — see lifespan
- When did the problem start? Sudden = part failure or environmental change. Gradual = wear/scale
- Any error code displayed? Tankless and combi units show specific codes — look up the code, don't replace parts blindly
- Any recent changes? Plumbing work, gas utility work, breaker tripped, water main repair
Brand-specific troubleshooting
- Rheem troubleshooting
- AO Smith troubleshooting
- Bradford White troubleshooting
- Rinnai troubleshooting
- Navien troubleshooting
Related guides
- Repair vs replace decision
- Parts directory
- Annual maintenance — preventing problems
Bottom line
Most water heater problems map to a specific symptom and a specific fix. Diagnose the symptom first; many problems are 30-minute DIY repairs once you know what to do. For tankless / combi units, the error code tells you exactly where to start — don't guess.