No hot water? What to check before you call a plumber
First figure out whether your water heater runs on gas or electricity, because the checks are different. On a gas heater the likely causes are the gas supply and the pilot or igniter. On an electric heater it’s usually a tripped breaker, a tripped reset button, or a burned-out heating element. Lukewarm water points somewhere else, and we cover that below.
Gas water heater: check the gas and the pilot
Make sure the gas is actually on. If the stove or furnace works, gas is reaching the house. Then find the shutoff valve on the gas pipe going into the water heater. The handle should run parallel with the pipe. If someone turned it off for another job and forgot, there’s your answer.
Smell gas? Stop what you’re doing and don’t touch any light switches or try to light anything. Get everyone out of the house, then call the gas company or 911 from outside.
Next, check the pilot. Older tank heaters have a small, always-on flame you can see through a little window near the bottom. If it’s out, there’s a label on the heater with relighting instructions. Follow those exactly. They’re written for your model.
If the pilot lights but goes out as soon as you let go of the knob, the thermocouple or flame sensor is the likely problem. It’s a common, cheap part, but on a gas appliance we’d leave it to a plumber.
A lot of newer gas heaters use electronic ignition, so there’s no pilot to relight by hand. These usually have a status light that blinks a code, and the label or manual explains it. Some plug into an outlet, so check the GFCI outlets in the garage. When one trips, it can take the water heater down with it.
Electric water heater: breaker, reset button, elements
Find the water heater breaker in your panel. It’s usually a double breaker. If it tripped, it’ll be sitting in the middle or in the off position. Push it fully off, then back on.
If the breaker looks fine, check the high-limit reset button. It’s a safety switch that cuts power when the water gets too hot, and it lives behind the upper access panel on the side of the tank.
- Turn the water heater breaker off. Don’t skip this. There’s live 240-volt wiring behind that panel.
- Take off the upper access panel with a screwdriver and fold back the insulation.
- Look for a red button, usually above the thermostat. Press it firmly. If it clicks, it had tripped.
- Put the insulation and panel back, then turn the breaker on.
- Give the tank an hour or so to heat before you decide whether it worked.
If the button trips again, don’t keep pressing it. Something is making it trip, usually a bad thermostat or a shorted element, and resetting it over and over just hides the problem. That’s when to call.
If the breaker and the reset button are both fine, a burned-out heating element is next. Testing one takes a multimeter and some comfort around 240 volts. If you don’t have both, leave it for a plumber.
Why is my water lukewarm instead of cold?
Lukewarm usually means the heater is running, just not well. The common causes:
- One element is out on an electric tank. With a dead lower element you’ll get a few minutes of hot water, then it fades fast.
- The thermostat got turned down or bumped. On electric units it sits behind the access panels, so the breaker goes off before you touch it.
- The dip tube broke. That’s the plastic tube that carries incoming cold water down to the bottom of the tank. When it cracks, cold water pours in at the top and mixes with the hot on its way out. Little bits of white plastic in your faucet screens are a clue.
- The tank is too small for how you use it now. If the first shower is hot and the third one is cold, and nothing else has changed, you may have outgrown it. Maybe you added a bathroom or a couple of teenagers.
Tankless water heater: error codes, gas and scale
Most tankless units show an error code on a display, and the manual or the maker’s website explains each one. Write it down. It’ll save time if you end up calling.
On gas tankless heaters, gas supply is a common problem. Make sure the gas valve to the unit is open. If the gas line is undersized, the heater can cut out when the furnace and range are running too. Check that the vent outside isn’t blocked by leaves or a wasp nest.
Scale is the other big one. Minerals build up inside the heat exchanger, and the unit starts overheating, shutting down, or swinging between hot and cold. Most makers call for descaling about once a year, and more often with hard water. Some Huntsville homes get noticeably harder water than others, and our post on hard water in North Alabama explains why.
And if only one faucet runs cold, pull its aerator and clean it. Tankless heaters need a minimum amount of flow before they fire, and a clogged aerator can drop a faucet below that.
When to stop and call a plumber
Call if the reset button keeps tripping, if the pilot won’t stay lit, or if you find water around the base of the tank. A leak at the bottom is its own problem, covered in water heater leaking from the bottom. Call too if it’s an older heater and this keeps happening. How long water heaters last covers when another repair stops making sense.
If you’re standing in front of the heater and not sure what you’re looking at, stop there. One cold shower beats guessing around a gas valve or live wiring.