First, narrow it down
Is the water ice cold, or lukewarm? Cold means the heater isn’t heating at all, think power, gas, or pilot. Lukewarm points at a failed element (electric), sediment buildup, a bad dip tube, or a mixing problem. And if the hot water just runs out fast, that’s a capacity symptom, not a failure, a different diagnosis entirely.
Also check: is it the whole house? One lukewarm faucet is usually that fixture’s cartridge mixing in cold, not the heater.
The checklist
Work through these in order, and stop at the first “call a pro” condition you hit.
Electric: check the breaker, reset once
A tripped water heater breaker is common and sometimes innocent. Reset it one time. If it trips again, stop, a shorted element or wiring fault is tripping it for a reason.
Electric: suspect an element
If you have some hot water but it runs out in minutes, one of the two heating elements has likely failed. That’s a repairable part on a heater worth repairing.
Gas: check the pilot and error codes
Follow the lighting instructions on the heater’s label exactly. If the pilot won’t stay lit, the thermocouple or gas control is likely failing, stop relighting and call.
Gas: if you smell gas, leave
Do not relight anything. Leave the area and call the gas utility from outside. This is the one non-negotiable step on the list.
Any leak at the tank: plan replacement
Fittings and valves are repairable; a tank leaking from its seam or base is not. Shut off the cold inlet and the power or gas, and get a replacement quote.
“Reset the breaker once. If it trips twice, it’s not a glitch, it’s a message.”
The bottom line
If the heater is 10+ years old and failing, put the repair money toward replacement, especially if it lives in an attic or above finished space, where its eventual leak is a renovation. A same-day replacement beats a slow-motion emergency every time.