Home › Answers › No hot water

No Hot Water? What to Check First

Last updated October 15, 2026.

Safety first: If you smell gas, leave now and call the gas utility or 911 from outside. If a CO alarm sounds, get everyone outside and call 911. If hot water or steam is spraying from the heater or its relief pipe, stay back. For a serious burn, call 911.

Most no-hot-water calls come down to four things: the heater lost power or gas, it locked out on a code, it ran out of stored hot water, or (tankless) the flow is too low to start it. You can check all four without opening anything.

Causes, most common first

1. A safety lockout or code. Gas tanks blink a status light; tankless units show a code. Writing it down is the fastest route to a fix. See the tankless error-code page.
2. Gas supply. Is the stove working? On propane, check the tank gauge. A gas shut-off handle usually lines up with the pipe when open. Look, don’t turn it.
3. Power. Electric and heat-pump tanks need 240 V; many tankless units need a 120 V outlet. Look at the breaker. If it’s tripped, leave it and call (we never reset breakers on water heaters; a trip means a fault).
4. Ran out. A tank needs time to recover after heavy use. Check again after the recovery time your manual lists, or later the same day.
5. Tankless minimum flow. Navien needs at least 0.5 gal/min; Noritz starts at 0.5 GPM (manuals). A barely open tap may stay cold.
6. Heat pump in a cold room. A.O. Smith switches to electric below 45 °F room air (Use & Care pp. 20–21).

Checks and fixes you can try

• Read and record the code or blink count.
• Tankless: one front-panel Reset if your manual allows (Navien), the unplug-replug restart on a cord-and-plug Rheem RTGH when the cord, plug and outlet are dry and undamaged, or on a Noritz NCC199CDV code 11 the remote power off → open a hot tap → power on (Owner’s Guide, p. 42). Once only. Never flip a breaker to reset.
• Clear snow or leaves from an outside vent by hand, from the ground.
• Heat pump: check the mode is Hybrid or Heat Pump; clean the filter if your manual says to leave power on (GE, Bradford White).
• Gas tank warm but never hot: turn the temperature dial one mark, as your manual shows, and check the water at a tap before anyone uses it.

It’s not normal if

The code comes back after one reset; the breaker trips; the pilot is out (relighting is a pro job here); you see water at the base; the vent is damaged or iced.

Is this normal?

A short cold burst between runs of hot water is common on a tankless heater — the burner pauses and restarts. Between back-to-back showers, leave a short gap or keep the hot tap running steadily instead of turning it off and on. If it keeps happening every time, use the cold-water sandwich steps in this guide.

Know exactly why not

A returning code means a real fault (gas pressure, flame sensing, venting or a sensor) that needs testing inside the cover. A tripped breaker on a water heater usually means a shorted element or wiring at 240 V. A pilot that won’t stay lit points at the thermocouple or gas control: gas work.

Start the guided check and choose Water heater.

Sources

• Navien NPE-2, pp. 9, 15–16
• Noritz NCC199CDV Owner’s Guide, pp. 39, 42, checked October 15, 2026
• Rheem RTGH, pp. 74–75
• A.O. Smith 100277324, pp. 20–21
• GE GeoSpring, p. 10

Related

• Tankless water heater error code
• Water heater leaking
• Water heater maintenance checklist

Independent information, not an inspection or a confirmed diagnosis. Not attorney-reviewed and not a licensed HVAC review. support@secondwrench.co