Does power vent water heater run continuously?

A power vent water heater, also known as a power vented gas water heater, is a type of tank-style water heater that utilizes a fan to push exhaust gases created from heating water out of the home through a dedicated vent pipe. Understanding how a power vent water heater operates can help homeowners determine if it is functioning properly or if repairs may be needed.

How a Power Vent Water Heater Works

Power vent water heaters have a combustion chamber where gas is burned to heat water stored in an insulated tank. Cold water enters the tank, gets heated by the burning gas, and hot water exits the tank when a hot water tap or appliance is turned on. As the gas burns, exhaust gases are created that need to be vented outside of the home. This is where the power vent comes into play.

The power vent consists of a fan and ductwork that connects to a dedicated exhaust vent pipe that terminates outside. When the water heater burner turns on, the fan also turns on to vent the exhaust gases through the ductwork and vent pipe. This creates a negative pressure in the combustion chamber that pulls in fresh air for combustion through a separate opening in the water heater. The fan and vent pipe allow the gases to be vented horizontally or vertically through the wall or roof.

On a standard natural draft water heater, the hot exhaust gases rise through the flue and create airflow to vent the gases. But the power vent fan does all the work to push the exhaust gases out. This allows a power vent water heater to have more flexible venting options because it does not rely on natural draft ventilation.

Main Components and Operation

The main components of a power vent water heater include:

• Insulated storage tank – Stores heated water.
• Gas burner – Heats water in the tank.
• Power vent assembly – Fan and ductwork that vents exhaust gases.
• Vent pipe – Typically PVC pipe that terminates outdoors.
• Air intake – Brings in fresh air for combustion.
• Gas control valve – Regulates gas flow to the burner.
• Temperature control – Allows setting desired water temp.

During normal operation:

1. Cold water enters the tank when hot water is used.
2. The gas burner turns on to heat the incoming cold water.
3. Exhaust gases from the burning gas accumulate in the combustion chamber.
4. The power vent fan turns on to vent the exhaust through the ductwork and vent pipe.
5. Fresh air is drawn in through the air intake.
6. The gas valve maintains proper gas flow to sustain combustion.
7. This cycle repeats to keep the water heated to the set temperature.

Do Power Vent Water Heaters Run Continuously?

A power vent water heater does not operate continuously like a boiler. Instead, it works in cycles, firing on and off, to maintain the temperature setpoint.

There are some instances where it may seem like the water heater is running nonstop:

• High hot water usage – During periods of heavy hot water demand, the water heater will cycle on more frequently to heat the cold water entering the tank.
• Faulty gas valve – If the gas valve fails to properly shut off gas flow when the tank reaches temperature, the burner may fire continuously.
• Thermostat issues – Problems with the temperature control or thermostat can lead to continuous heating.
• Sediment buildup – Excessive limescale accumulation on the burner or heat exchanger may allow the water to cool excessively before the burner cycles on again.

But during normal operation, as hot water is used, the burner will fire to heat the tank and then shut off once the set temperature is reached again. The length of the cycles depends on how much demand is placed on the heater.

Cycle Frequency

The amount of time a power vent water heater actually runs depends on:

• Temperature setting – A higher temperature setting results in longer run times.
• Climate – Colder incoming groundwater takes more heating.
• Usage – More use of hot water means more frequent heating cycles.
• Tank size – Larger tanks stay hot longer than small ones.
• Heating capacity – Higher BTU heaters recover temperature faster.

For example, a typical 40 gallon residential power vent heater may only run about 30-45 minutes per hour with moderate usage. If heavy use occurs back-to-back, it may run for 2-3 hours solid until the tank is heated up again. But it is not designed to run continuously without ever shutting off.

Burner On-Off Cycling

The burner on a power vent water heater will cycle on when:

• Water temperature drops below the thermostat set point.
• Incoming cold water causes tank temperature to fall.
• Hot water tap or appliance is opened allowing hot water to leave the tank.
• Thermostat calls for heat to bring water back up to temperature.

The burner will cycle back off when:

• Thermostat senses tank temperature rise to reach set point.
• Gas valve closes to stop gas flow to the burner.
• Power vent fan turns off once combustion stops.
• Heater awaits next heating cycle based on usage and standby losses.

This ignition – heating – shutdown sequence continues as thermostatically controlled cycles to maintain a constant hot water supply. Cycling too frequently may indicate a problem.

Continuous Operation Issues

If a power vent water heater is in fact running nonstop with no off cycles, there are some common causes to check:

Thermostat Malfunction

If the temperature control or thermostat is broken, it may fail to signal for the burner to turn off when set point is reached. The water in the tank will get dangerously hot with continuous heating. Replace a malfunctioning thermostat.

Gas Valve Defect

A defective gas control valve can get stuck open and allow nonstop gas flow to the burner. This will require replacement of the gas valve. Turn off water heater and call a technician immediately if suspected.

Sediment Buildup

Limescale and sediment accumulation on the burner or heat exchanger can prevent proper heat transfer to the tank water. This may allow the water to cool excessively before the burner turns on again for the next cycle. Flush the tank to clear any debris.

Insufficient Air Flow

If airflow is obstructed through the combustion chamber or flue, it can cause improper burner operation. Make sure the air intake and exhaust vents are fully open and unobstructed.

Power Vent or Thermocouple

If the power vent fan fails to turn on when the burner fires, dangerous exhaust gases can back up in the combustion chamber. The thermocouple that senses a pilot flame is needed for gas valve operation. Replace if defective.

How to Prevent Continuous Operation

Some tips to keep a power vent water heater cycling on and off normally:

• Set temperature only as high as needed. Lower temps mean shorter run times.
• Install heat traps on hot and cold lines to retain heat in the tank.
• Insulate hot water pipes to prevent heat loss in supply lines.
• Use timers to limit burner operation during peak usage.
• Drain and flush tank yearly to control sediment buildup.
• Check venting for blockages or leaks.
• Replace the anode rod to protect against corrosion.
• Have heater serviced by a professional every 1-2 years.

Signs of Abnormal Operation

Be aware of the following signs that may indicate a problem with continuous heating:

• Burner never shuts off, even overnight or with no hot water use.
• Power vent fan runs nonstop.
• High surface temperatures on the tank jacket or supply pipes.
• Rumbling or roaring noises from the burner.
• Soot building up around the exhaust vent or intake.
• Hot water scalding or too hot at faucets.
• Higher than normal gas bills for your household.

Determining if your power vent heater is experiencing abnormal continuous operation will help prevent hazards or wasted energy usage. Call a professional to inspect and service the system if needed.

Conclusion

Power vent water heaters are designed to cycle on and off to maintain hot water storage temperatures, not to run continuously. Frequent hot water draws will increase burner firing to reheat the tank, which is normal. But nonstop operation without ever shutting off can signify various problems like thermostat failure, gas valve defects, insufficient airflow, or excessive sediment accumulation. Catching improper continuous operation early and identifying the cause can help restore normal heater function and safety.