Water Heater Fan Keeps Running: Normal or a Fault?
On this page (7 sections)
The Short Answer: It depends on the heater. A heat-pump (hybrid) water heater’s fan can legitimately run for an hour or more while it reheats the tank. A power-vent gas tank’s blower should stop within a short post-purge after the burner shuts off. A tankless fan should follow hot-water use. A fan that runs for hours with no demand, gets hot, or smells of burning needs service.
First, identify which fan you are hearing
| Heater type | What the fan does normally | When it is a problem |
|---|---|---|
| Heat-pump / hybrid electric (compressor and fan on top) | Runs with the compressor for long stretches while the tank recovers | Runs nonstop for days with the tank already hot, rattles, or the unit shows an alert |
| Power-vent gas tank (blower on top, plastic vent pipe) | Starts before the burner, runs with it, purges briefly after | Keeps running long after the burner is off, or runs with no burner at all |
| Gas tankless | Runs during hot-water use and briefly after | Runs for long periods with every tap closed and no recirculation schedule |
| Standard atmospheric gas tank (metal draft hood, no blower) | Has no fan | The noise is coming from another appliance |
Check the rating plate if you are unsure; identifying your water heater shows where to look.
Heat-pump water heaters: long run times are expected
A heat pump moves heat slowly compared with a burner or elements, so a recovery after showers can keep the compressor and fan running for a long time. Run time also grows in a cool room, in an “efficiency” or “heat pump only” mode, or when the air filter is dirty. If the filter is owner-serviceable per your manual, cleaning it is a reasonable first step. Persistent rattling or the fan running while the display shows the tank satisfied is a service issue; see hybrid water heater noise.
Power-vent gas tanks: the blower should stop
On a power-vent tank, the control turns the blower on, confirms airflow through a pressure switch, lights the burner, and then lets the blower purge the vent for a short time after the burner goes out. A blower that never stops usually points to the control not ending the cycle: a pressure switch or its sensing tube giving a false signal, a control board fault, or a thermostat call that never ends. These are diagnosed by a technician; do not disconnect the tubing or bypass the switch. The opposite problem, a blower that will not start, is covered in water heater blower not working.
Tankless units: look for something still calling for heat
A tankless fan that keeps running with no taps open may be responding to a recirculation pump or schedule, a dripping fixture, or a fault in the flow sensing. Some models also run components for freeze protection in cold weather, so check the owner’s manual before assuming a defect, and do not unplug an outdoor or garage unit in freezing weather. If the display shows a code, look it up in the manual for your exact model.
What you can check safely
- Note whether the burner or compressor is running with the fan, and for how long after hot water was last used.
- Close all fixtures and check for a dripping tap or a running toilet fed with hot water.
- Look at the status light or display and write down any code or flash pattern.
- Check whether a recirculation pump or timer is installed and when it runs.
- From outside, look at the vent termination for obvious blockage such as a nest or snow drift. Do not run a gas heater with a blocked vent.
What the technician will check
On a power-vent tank, the technician checks the pressure switch and its tubing, condensate in the vent or switch line, the vent run for blockage, and whether the control is releasing the blower relay at the end of a cycle. On tankless units they look at flow-sensor readings, recirculation settings, and the fault history. On heat-pump models they check airflow, the filter and evaporator coil, refrigerant performance, and fan motor condition. A worn motor bearing or failed capacitor is usually a part replacement, not a new heater.
Frequently Asked Questions
Q: How long should a power-vent blower run after the burner shuts off? A: Typically a short purge measured in seconds to about a minute, depending on the model. Your installation manual lists the sequence. Several minutes of blower with no burner and no call for heat is not normal.
Q: My heat-pump water heater fan runs most of the day. Is that wrong? A: Not necessarily. Heavy hot-water use, a cool installation room, or an efficiency-only mode can keep it running for long periods. Check and clean the air filter if your manual allows it, and switch to a hybrid mode if you need faster recovery.
Q: Can I unplug a power-vent heater to stop the noise? A: Unplugging it turns the whole heater off, which is safe, but you will lose hot water. Do not try to keep the burner running without the blower, and do not tamper with the pressure switch.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
- CPSC: carbon monoxide fact sheet (opens in a new tab)Carbon monoxide hazards and emergency response.
Editorial standards and corrections · Prepare a useful service request