"No hot water" is the single most common water heater complaint. The diagnostic path differs between gas and electric tanks.
Electric water heater — diagnostic sequence
- Verify breaker is on. 240V double-pole. Reset once if tripped. If trips again immediately, electrical fault — proceed to step 6
- Reset ECO — red Emergency Cutoff button on upper thermostat (under upper access cover). See reset guide
- Verify 240V at unit terminals with voltage tester
- Test upper thermostat continuity with multimeter
- Test upper element resistance — 4500W should read 10-16 Ω
- Element-to-ground short test — any continuity = element shorted, replace immediately
Gas water heater — diagnostic sequence
- Check pilot light (atmospheric units). If out, attempt relight per manual. See pilot light guide
- If pilot won\'t stay lit: thermocouple failure (most common). $15-25 part, 45-min DIY. See thermocouple guide
- If pilot stays lit but no main burner: gas valve or temperature sensor
- Verify gas supply — other gas appliances working confirms supply
- Modern DSI units: read LED flash codes or display fault
Common root causes
- Electric: tripped ECO (#1 cause), failed element, failed thermostat, tripped breaker
- Gas: failed thermocouple (#1 on atmospheric), out of gas, draft/venting issue, gas valve fault
- Both: sediment insulating sensor causing odd readings
When to call a pro
- Electrical fault that trips breaker repeatedly
- Gas leak suspected (smell of gas — leave the house, call utility)
- Element shorted to ground
- Gas valve replacement
- Unit is over 12 years old — consider replacement instead of repair
Bottom line
Electric: breaker → ECO → thermostat → element. Gas: pilot → thermocouple → gas valve. Most "no hot water" calls resolve with one of: breaker reset, ECO reset, or thermocouple replacement ($15-25 DIY). For aged units (12+ years), evaluate replacement vs repair.