A water heater that will not heat almost always fails at one of a small number of points: the power or gas supply, a safety switch that has tripped, a worn ignition part, a failed heating element or thermostat, or sediment that has built up faster than it should have. Which one applies depends heavily on whether the unit is gas, electric, tankless or a heat pump model, since each type fails in its own characteristic way.
How a water heater actually makes hot water
Every storage tank water heater does the same basic job: it holds a tank of water and applies heat until the water reaches a thermostat's set point, then holds that temperature by cycling on and off. A gas unit applies heat with a burner under the tank; an electric unit applies it with one or two heating elements inside the tank. A tankless unit skips the tank entirely and heats water as it flows past a heat exchanger, on demand. A heat pump unit pulls warmth out of the surrounding air and moves it into the water, using a small backup electric element when it needs a fast recovery. Understanding which of these four systems you have is the first step in troubleshooting, because "not heating" means something different in each one.
Start with these safe checks
- Check whether it is every faucet, or just one. If only a single tap runs cold, the fixture or its mixing valve is the likely problem, not the heater itself.
- Electric heater: check the breaker panel. If the breaker for the water heater has tripped, reset it once. If it trips again immediately, stop and call, since a part has likely failed to ground.
- Gas heater with a standing pilot: look at the pilot window. If the pilot is out, the printed instructions on the heater's own label explain the exact restart sequence for that model. Follow them once.
- Tankless or heat pump unit: read the display. Most of these units show an error or fault code rather than simply going cold. Write the code down along with the model number before you call.
- Check the thermostat setting. A dial or digital setting that has been bumped, or a recent power outage, can leave a perfectly healthy heater sitting at too low a temperature.
- Think back over the last day or two. A power outage, recent plumbing work, or the house sitting empty can all explain a cold tank without any part having failed.
Gas water heaters: why they stop heating
On a standard gas storage tank, the ignition system is the part most likely to be at fault. A worn thermocouple or flame sensor is the single most common cause of a pilot that will not stay lit or a burner that will not fire, because that sensor's only job is to prove a flame is present before it allows gas to flow. When it degrades, it can shut the system down even though everything else works fine.
| What you notice | Usual cause | What a technician checks |
|---|---|---|
| Pilot won't stay lit | Worn thermocouple or flame sensor, drafts, a partly blocked vent | Ignition system, venting, draft at the flue |
| Pilot is lit but the burner won't fire | Failed gas control valve or a dirty burner orifice | Gas control valve, burner assembly, gas pressure |
| Water never gets more than lukewarm | Failed thermostat inside the gas control, low incoming gas supply | Gas control thermostat, supply pressure |
| Not enough hot water for the household | Sediment buildup or a broken dip tube | Tank condition, dip tube, sediment depth |
Full repair detail, including what a technician actually does on a gas call, is on our gas water heater repair page.
Electric water heaters: why they stop heating
Electric tanks run on 240-volt circuits with two heating elements: an upper element and a lower element, each controlled by its own thermostat, plus a shared high-limit safety switch that cuts power if the water gets dangerously hot. When there is no hot water at all, the upper element, its thermostat, or the high-limit switch is usually to blame. When hot water runs out fast but the first few minutes are fine, the lower element has typically failed instead.
| What you notice | Usual cause | What a technician checks |
|---|---|---|
| No hot water anywhere in the house | Failed upper element, bad upper thermostat, or a tripped high-limit switch | Voltage at the unit, both thermostats, the high-limit reset |
| Hot water runs out after a few minutes | Failed lower element or a broken dip tube | Lower element resistance, dip tube condition |
| Breaker trips whenever the heater runs | An element that has shorted to the tank (grounded out) | Element resistance to ground, wiring and connections |
| Water comes out scalding hot | A thermostat stuck in the closed position | Both thermostats, the high-limit switch |
The step-by-step process we follow on an electric call is covered on our electric water heater repair page.
Tankless and heat pump units: a different failure pattern
Tankless heaters rarely go from working perfectly to completely dead. More often they throw an error code tied to ignition, water flow, or a scaled-up heat exchanger, and the display tells you which. Heat pump water heaters can behave the opposite way: rather than going cold, they quietly fall back on their backup electric element and keep working, just at a higher electricity cost, until that backup element eventually fails too. Both are covered in more depth, including full code and cause tables, on our tankless water heater repair and heat pump water heater repair pages.
Hot water heater not heating or stopped heating water: what changed?
When a water heater that worked yesterday stops heating, something changed. A power outage, a tripped breaker, a pilot that went out, a thermostat that was bumped, new plumbing work or a long absence can each leave a healthy heater cold. A heater that fades gradually, taking longer to heat or running out sooner, usually points to sediment, a failing element or a worn burner part instead. If the cause is a gas pilot, see our guide to a water heater pilot light that is out or won't stay lit. If it is a tankless unit, read why a tankless water heater is not heating.
Sediment: the cause hiding behind many "no heat" calls
On any storage tank, mineral sediment settles to the bottom over months or years. A thin layer is normal. A thick layer insulates the water from the heat source, so the burner or element runs longer to do the same job, and eventually the tank cannot keep up with demand at all. This is also the most common cause of popping and rumbling sounds, which we cover in detail in our guide to water heater noises. A yearly flush, described in our maintenance checklist, is the single best way to prevent a sediment-related "no heat" call in the first place.
When to stop troubleshooting and call a professional
Beyond that immediate safety line, stop and call once a breaker has tripped a second time, once a pilot has gone out more than once in a short period, or once you notice rust-colored water, moisture at the base of the tank, or an unfamiliar smell. None of those are DIY situations, and continuing to reset a failing part can turn a simple repair into a full replacement.
Frequently asked questions
Why do I have hot water in the kitchen but not in the shower?
That pattern points to the shower valve or its cartridge rather than the water heater, since the heater is clearly still supplying hot water to at least one fixture in the house.
How long does it take to get hot water back after a repair?
A storage tank needs time to reheat a full tank of cold replacement water after any repair that involved draining it. We will give you a realistic window on site based on your specific unit.
Is a "no hot water" call an emergency?
It is disruptive but not inherently dangerous on its own. If it is paired with a leak, a gas smell, or a breaker that keeps tripping, treat it as urgent and see our emergency water heater repair page.
What if the tank itself turns out to be the problem?
If the tank has failed or is actively leaking, repair is no longer possible and we will walk you through replacement, covered in full in water heater repair vs replacement.
We take no-hot-water calls across Lake Stevens 24 hours a day, including Old Town, South Lake Stevens and every neighborhood in between. See our no hot water repair service page for what a visit involves.