If your water heater stopped making hot water, the most likely culprits are a tripped breaker, a burned-out heating element, a failed thermostat, or (on gas units) a problem with the gas valve or pilot. None of these require you to take the heater apart to diagnose. Here’s what’s probably going on.
The Most Common Causes, in Order
Tripped breaker (electric heaters)
Start here before anything else. Electric water heaters pull a lot of amps, and the breaker trips more often than people expect. Go to your electrical panel, find the breaker labeled for the water heater (usually a 30A double-pole), and see if it’s in the off or middle position. Reset it once. If it trips again immediately or within a day, stop there. That’s a sign of a short or a failing element drawing too much current. A licensed plumber or electrician needs to look at it.
Burned-out heating element (electric heaters)
Most electric tank heaters have two elements, upper and lower, each controlled by its own thermostat. When the lower element fails, you’ll often get some hot water but it runs out fast. When the upper element fails, you get nothing at all. A plumber tests each element with a multimeter to check whether it’s still functional. Replacing an element means draining part of the tank, working around 240V wiring, and dealing with sediment that may have built up over years. It’s a job for a licensed plumber.
Failed thermostat
Each element on an electric heater has a thermostat behind an access panel on the side of the tank. Thermostats can fail in two ways: they stop calling for heat (so the element never turns on), or they stick in the “on” position, which drives water temperature up until the high-limit cutout trips and shuts everything down. The high-limit cutout is part of the upper thermostat assembly, accessed through the upper panel. There’s a red reset button on it. If it’s popped, you can press it once. If it trips again, the thermostat or element is probably bad and needs replacement.
Pilot light or ignition failure (gas heaters)
On older gas heaters with a standing pilot, check the small window near the bottom. If the pilot is out, there are relighting instructions on the label of the unit itself. Follow them. If you relight it and it won’t stay lit, the thermocouple is likely worn out. That’s the small metal probe that sits in the pilot flame and signals the gas valve it’s safe to stay open. Thermocouples are inexpensive parts, but getting to them and replacing them correctly is a job for someone with gas work experience.
Newer gas heaters use electronic ignition. If you hear clicking but no ignition, or no clicking at all, the igniter or the control board may have failed.
Gas valve failure
The gas valve controls the flow of gas to both the pilot and the main burner. When it fails, you often get a pilot that lights but a burner that won’t fire. Newer units have a status light (a small LED on the gas control valve) that blinks error codes. The code meanings are manufacturer-specific and printed on a sticker on the unit itself, usually near the burner door or on the valve. Gas valve problems are not a homeowner repair. If you suspect the valve, turn the gas supply off at the shutoff behind the heater and call a plumber.
Sediment buildup
Hard water areas like much of the Bay Area accumulate mineral deposits at the bottom of the tank over time. Heavy sediment insulates the water from the burner or element, which can make the heater work so hard it trips the thermal cutout. You might hear popping or rumbling sounds during a heating cycle. This isn’t an emergency, but it does shorten heater life, and a technician may recommend flushing or replacement depending on how bad it is.
What a Technician Actually Does
A plumber diagnosing a dead water heater goes through this pretty fast. On an electric unit: check power at the panel, check the reset button, pull the access panels and test element resistance and thermostat continuity. On a gas unit: verify gas supply is on, check the pilot or ignition system, read the status light blink code if present, test thermocouple millivolt output. Most of the time the diagnosis takes 15 to 30 minutes and points clearly to one part.
What’s Safe to Do Yourself
You can reset a tripped breaker once. You can relight a standing pilot following the printed instructions on the unit. You can check that the gas shutoff valve is open and that other gas appliances in the house are working (which rules out a supply interruption). That’s about it.
Don’t attempt to replace elements, thermostats, thermocouples, or gas valves yourself unless you have specific training. The risks are real: 240V wiring, scalding water under pressure, and gas. The money you save rarely covers the cost of the follow-up call to fix what went wrong.
When to Call a Licensed Plumber
If the breaker trips again after one reset, if you smell gas anywhere near the unit, if the pressure relief valve is dripping, or if you still don’t have hot water after the basic checks above, call a licensed plumber. California requires plumbers to hold a C-36 license from the Contractors State License Board. You can verify any contractor’s license at cslb.ca.gov before work begins.
This site is an information resource, not a plumbing company. We don’t offer plumbing services or pricing. The purpose is to help you understand what you’re dealing with before you pick up the phone, so you can have a more useful conversation with the person doing the work.