Step 1: Identify Your Water Heater Type
The troubleshooting steps differ significantly between tank water heaters (the traditional large cylinder) and tankless water heaters (the wall-mounted box). Both can be gas or electric. Knowing which you have narrows down the possible causes quickly.
No Hot Water — Gas Tank Heater
If you have a gas tank water heater with no hot water, the most common causes are: (1) The pilot light is out — check the pilot window and follow the relight instructions on the heater label. (2) The thermocouple has failed — this is the sensor that keeps the gas valve open when the pilot is lit. A failed thermocouple is a $20–$50 repair. (3) The gas valve itself has failed — this requires a professional repair. (4) The gas is off — check other gas appliances to confirm your gas supply is working.
No Hot Water — Electric Tank Heater
For an electric tank heater with no hot water: (1) Check your circuit breaker — a tripped breaker is the most common cause. Reset it and wait an hour. (2) If the breaker is fine, the upper heating element or thermostat has likely failed. These are serviceable parts. (3) If the unit is 10+ years old and the element has failed, replacement is often more cost-effective than repair.
Lukewarm Water — Not Enough Hot Water
Lukewarm or insufficient hot water from a tank heater usually means: (1) The thermostat is set too low — check the dial on the side of the tank and set it to 120°F. (2) The lower heating element has failed (electric heaters). (3) Sediment buildup has reduced efficiency — a tank flush or descale service is needed. (4) Your tank is simply too small for your household's demand — consider a larger unit or a tankless upgrade.
Tankless Water Heater Problems
Tankless water heaters display error codes when something is wrong. The most common issues include: (1) Ignition failure — often caused by a gas pressure issue or a dirty burner. (2) Minimum flow not met — some tankless heaters require a minimum flow rate to activate. (3) Scale buildup on the heat exchanger — LA's hard water causes rapid mineral buildup in tankless heaters. Annual descaling service is essential. (4) Venting issues — blocked or incorrectly sized venting causes shutdown.
Water Heater Leaking
A water heater that is leaking from the tank itself (not from a fitting) is at end-of-life and must be replaced immediately. Leaks from fittings (pressure relief valve, cold water inlet, hot water outlet) can often be repaired. Do not ignore any water heater leak — even a small one can cause significant water damage.
When to Call a Professional
Call Plumbing 405 immediately if: the tank is leaking; you smell gas; error codes won't clear after basic reset; the breaker keeps tripping; water has rust or unusual smell; the unit is 10+ years old and having problems. We offer same-day water heater service throughout Greater Los Angeles.