Water Heater Not Heating
Work through these in order. And know where the list stops and a licensed professional starts.
No hot water at all has a short list of causes. On electric: a tripped breaker, a tripped high-limit reset button, or failed elements or thermostats. On gas: the pilot or igniter, the thermocouple, or the gas supply. Check the breaker and the reset button first — between them they are a large share of all cases.
First, three questions
- Is it no hot water at all, or lukewarm water? No hot water means the heat source is not working — this page. Lukewarm or insufficient means a different diagnosis: running out of hot water.
- Is it one tap or every tap? One tap is a fixture problem — a cartridge, an anti-scald stop, or a blocked aerator — not a water heater problem.
- Has anything else changed? A power cut, a storm, work in the house, or a new appliance. Context is diagnostic.
Electric: the checks, in order
Check the breaker
Look for a tripped double-pole breaker in the panel. Reset it once. If it trips again immediately, stop — a repeatedly tripping breaker means a fault, and chasing it is electrician's work.
Press the high-limit reset
Behind the upper access panel there is a red reset button, the ECO or high-limit switch. If it has tripped, press it. This is a large share of all no-hot-water calls on electric tanks.
Note whether it trips again
A reset that holds means it was a one-off, often after a power event. A reset that trips again points at a failed thermostat or a shorted element, which is a parts replacement rather than a reset.
Have the elements and thermostats tested
A continuity test on both elements and both thermostats takes a technician minutes. Both are inexpensive parts. This step involves working inside a live appliance — have someone qualified do it unless you genuinely know how to isolate and test safely.
Check the tank is actually full
Rare, but an air-locked or partly empty tank after plumbing work will not heat properly and can damage an element. Purge air at a hot tap until water runs steadily.
Procedure: Diagnose an electric water heater with no hot water
Gas: the checks, in order
Confirm gas is reaching the house
Is your gas range or furnace working? If nothing gas-fired is working, this is a supply problem rather than a water heater problem.
Check the gas control setting
Make sure it has not been set to Pilot or Off — after a vacation, a service visit, or someone tidying a utility room, this happens more often than you would think.
Look at the pilot or igniter
On an older unit with a standing pilot, look through the sight glass: is it lit? On a modern unit there will be an igniter and usually a status light or error code. Read the code in the manual rather than guessing.
Try relighting the pilot, once, by the label
Follow the instructions printed on the unit exactly. If it will not light, or will not stay lit, stop. A pilot that will not hold usually means a failed thermocouple or a gas control fault, and both are licensed work.
Check the flue is clear
A blocked flue or a backdrafting appliance can shut a unit down on safety, and it is a carbon monoxide hazard. If you suspect it, stop and call a professional the same day.
Stop here
Beyond the pilot and the control setting, gas water heater diagnosis is licensed work. The parts are cheap and the risk is not.
Procedure: Diagnose a gas water heater with no hot water
What each symptom usually means
| Symptom | Electric | Gas |
|---|---|---|
| No hot water at all | Tripped breaker, tripped high-limit reset, or both elements or thermostats failed | Pilot out, failed thermocouple, gas supply, or control fault |
| One short burst then cold | Failed lower element — the commonest electric fault | Not typical; check the dip tube |
| Lukewarm but plentiful | Thermostat setting or a failed thermostat | Thermostat setting, or a partly blocked burner |
| Breaker trips repeatedly | Shorted element or wiring fault — stop, call an electrician | Not applicable |
| Reset button keeps tripping | Failed thermostat or shorted element | Not applicable |
| Pilot will not stay lit | Not applicable | Failed thermocouple, or a flue or combustion air problem — call a professional |
| Error code on the display | Look it up in the manual | Look it up in the manual |
Where the line is
You can safely: reset a breaker once, press the high-limit reset button, check the gas control setting, relight a standing pilot per the label, purge air from the system, and read an error code.
You should not: chase a repeatedly tripping breaker, test components inside a live appliance without knowing how to isolate it, work on a gas control or a thermocouple, or alter venting. All of those are licensed trades in most jurisdictions, and the parts involved are inexpensive relative to the risk.
Before you spend money on a repair
Check the age of the unit. A failed element on a six-year-old tank is an obvious repair. The same part on a fourteen-year-old tank is money spent on an appliance at the end of its expected 10 to 15 year life, and the tank is the thing that will fail next. Replace or repair.
What goes in with it
A water heater is a system, not a box. These are the parts that go in with it, and the ones people discover they need halfway through the job.
- Expansion tank
Required by code on a closed system, which is most homes with a pressure-reducing valve.
- Drain pan
Cheap insurance anywhere the tank sits above something you care about.
- Anode rod
The part that decides when the tank leaks. Replacing it is the highest-value hour of maintenance there is.