How to Safely Turn On a Hayward Pool Heater

Check Water Flow and Open Gas Valves Before Starting

Your pool heater should never run without water moving through it first. The unit transfers intense heat into metal water heating tubes (the heat exchanger) as water circulates back to your pool. If the heater fires while dry, the extreme temperature will warp the tubes and melt internal plastic parts within seconds.

Every Hayward unit relies on a water flow safety sensor (a pressure switch) to prevent dry firing. This sensor monitors the water pressure created by your circulation pump. If the pump is off, or if the pressure drops too low, the sensor cuts power to the ignition system. The heater will not even attempt to spark until water flows freely.

Complete these simple checks before touching any heater controls:

• Turn on the pool pump: Start your main circulation pump and wait for it to prime fully. Look through the clear pump lid to confirm the basket is full of water and free of large air bubbles.
• Empty the strainer baskets: Clean out both the skimmer baskets and the pump strainer basket. Packed leaves or pine needles choke water flow and drop system pressure below the safe operating limit.
• Inspect the pool filter: Check the pressure gauge on top of your filter tank. If the reading sits higher than normal, backwash your sand filter or rinse your filter cartridges before turning on the heater.
• Open all return line valves: Check the plumbing valves between the pool pad and the swimming pool. Make sure the valves directing water to the heater and return jets are open. If your plumbing includes a heater bypass line, ensure the bypass valve is closed so water routes directly through the heater.
• Open the gas supply line: Look at the gas pipe entering the side of the heater cabinet. Find the manual gas shutoff valve, which has a small lever handle. Turn the lever so it runs parallel with the pipe to open the gas line. If the lever sits perpendicular (across the pipe), the fuel is shut off.
• Check fuel levels for propane: If your system runs on liquid propane rather than utility natural gas, check your storage tank gauge. Pool heaters consume large amounts of fuel. If your propane tank drops below 20 percent, it may lack the vapor pressure needed to ignite the burners.

Turn On Digital Models Using the Mode and Temperature Buttons

Most modern Hayward heaters, including Universal H-Series models, feature an electronic control panel with a digital display. These units manage the entire ignition process automatically once you select your settings. Follow these sequential steps to start your digital heater safely.

1. Turn on electrical power: Switch on the electrical breaker dedicated to your pool heater inside your main panel or pool subpanel. Many setups also include an outdoor toggle switch mounted on the wall or on the heater cabinet. Flip that switch to the on position.
2. Check the display screen: The digital screen should illuminate immediately. If the heater is in standby mode, the screen will read "OFF" or "bO" (bypass operation). You may also see the current water temperature displayed on the screen.
3. Press the Mode button: Locate the button labeled "MODE" on the keypad. Press it once or twice until the indicator light beside "POOL" illuminates. If you are heating an attached hot tub, press the button until "SPA" is selected instead.
4. Set your desired temperature: Use the Up and Down arrow buttons to adjust the target temperature. As you press the arrows, the numbers on the screen will change to show your chosen setpoint. For everyday swimming, most pool owners set the temperature between 78 and 82 degrees Fahrenheit. Stop pressing the buttons once you reach your target number, and the screen will blink before locking in the setting.
5. Wait for the automatic ignition cycle: Once the setpoint is higher than the current water temperature, the heater begins its startup sequence. You do not need to push any other buttons. The internal control board will run through several automatic safety checks before lighting the burners.
6. Listen for proper operation: You will first hear a small exhaust fan (the draft blower) begin to hum. This fan runs for 15 to 30 seconds to purge lingering fumes from the combustion chamber. Next, you will hear a faint electrical click as the igniter activates, followed by a heavier click when the internal gas valve opens. Within seconds, a soft whoosh indicates the main burners have lit.
7. Confirm warm water at the pool: Let the heater run for three to five minutes. Walk over to your pool and place your hand directly in front of a return jet. The returning water should feel distinctly warmer than the rest of the pool water.

Light Older Manual Heaters by Lighting the Pilot Flame First

Older Hayward heaters without digital display screens use a millivolt system. These heaters do not connect to a household electrical outlet. Instead, they generate their own tiny electrical current using a small starter flame (a pilot light) and a heat-sensing probe called a thermocouple.

Starting an older millivolt heater requires lighting this starter flame manually. The process is simple, but you must follow the safety pauses strictly to avoid gas buildup inside the cabinet.

Start by removing the front door or lower access panel of the heater. Look inside the cabinet to locate the gas control valve, which is a metal box with a round plastic knob on top. The knob has three positions: OFF, PILOT, and ON. If the knob is currently set to ON, turn it clockwise to OFF.

Wait five full minutes before attempting to light the unit. This pause lets any residual gas escape into the open air. Sniff near the bottom of the cabinet. If you smell gas, stop immediately, wait longer, and check for leaks.

Once the air is clear, turn the gas control knob to PILOT. Push down firmly on the knob and hold it down with your thumb. Pushing the knob opens a small internal port that sends gas only to the pilot burner hood.

Keep holding the knob down while you reach inside with a long-stem grill lighter. Place the flame right next to the pilot burner hood beneath the combustion chamber. When the pilot flame catches, continue holding the knob down for 45 to 60 seconds.

Holding the knob down allows the small starter flame to heat up the thermocouple rod. When the metal rod gets hot, it generates an electrical current that tells the safety valve to remain open. After 60 seconds, release the knob slowly. The pilot flame should stay lit on its own.

If the flame goes out immediately after releasing the knob, turn the valve back to OFF, wait five minutes, and repeat the process. Once the pilot flame stays lit steadily, turn the knob counterclockwise to ON. Finally, turn the mechanical thermostat dial on the outside of the heater up to your desired temperature. The main burners will light automatically across the entire burner tray.

Fix Common Error Codes Like LO and IF in Minutes

Digital Hayward heaters monitor operating conditions constantly. When a sensor detects an issue, the display shows a two-letter error code instead of firing. Understanding these codes helps you fix the issue quickly without calling for service unnecessarily.

• The LO error code (low water flow warning): This is the most common code pool owners encounter. It means the water flow safety sensor does not detect enough water pressure to let the heater fire safely.
  • Check your skimmer baskets and pump basket for leaves, hair, or debris that restrict water flow.
  • Look at your pool filter pressure. A dirty filter blocks water flow drastically. Backwash your sand or DE filter, or spray down cartridge elements to restore full pressure.
  • If you have a variable speed pump, verify the running speed. Low energy-saving speeds often fail to push enough water through the heater. Increase the pump RPM until the LO code clears.
  • Make sure all return line valves are fully open.
• The IF error code (ignition failure warning): This code appears when the heater tries to light its burners three consecutive times and fails. The system locks itself out to prevent raw gas from collecting in the cabinet.
  • Verify that the external manual gas shutoff valve is completely parallel to the pipe.
  • If the heater has been off all winter, air may be trapped inside the fuel line. Turn the heater power off, wait 30 seconds, and turn it back on to let the unit attempt ignition again.
  • For propane systems, confirm your supply tank has adequate fuel. Low tank pressure frequently causes ignition failure on startup.
  • If your digital screen stays locked on this warning, read our guide on how to reset a Hayward pool heater to clear the control board memory safely.
• Heater clicks repeatedly without igniting: If you hear the igniter spark or the internal gas valve click, but no flame appears, fuel is not reaching the ignition zone. Check that your gas supply valve is open. In older or neglected units, spiders and dirt daubers often build small nests inside the burner tubes or pilot hood, blocking gas flow.
• The digital screen remains completely blank: If the control panel does not light up at all, check your electrical supply. Confirm the breaker in the main panel has not tripped. Look for an external service switch near the pool pad and ensure it is turned on. Also, verify that your pool automation panel or pump timer is actively powering the pad equipment.

Shut Off the Gas Immediately If You Smell Rotten Eggs

Pool heaters burn high volumes of fuel to generate heat rapidly. While modern heaters feature robust safety systems, gas combustion always requires caution. You must know the warning signs that indicate immediate danger so you can shut down the equipment safely.

The most serious warning sign is the distinct smell of sulfur or rotten eggs around the pool equipment pad. Utility companies add this odor to natural gas and propane so human senses can detect leaks immediately. If you smell gas near the heater, do not press any buttons on the control panel, do not flip electrical switches, and do not use a phone near the pad. Any tiny electrical spark can ignite lingering gas fumes.

Back away from the equipment pad immediately. If you can reach the manual gas shutoff valve safely from a distance, turn the lever perpendicular to the pipe to stop the fuel flow. Step well away from the area, keep children and pets clear, and call your local gas utility provider or the fire department from a safe distance.

Watch for signs of flame rollout or black soot around the heater cabinet. Flame rollout occurs when flames escape out from underneath the combustion chamber or lick through the edges of the access panel instead of rising through the exhaust vent. This happens when the metal water heating tubes become clogged with soot, leaves, or rodent nesting material. If you see flames escaping the cabinet or notice black soot stains on the outside tan panels, turn off the electrical power and gas supply immediately.

Listen for unusual sounds during operation. A smooth heater produces a steady whir from the fan and a gentle roar from the burners. If you hear loud banging or popping sounds, unburned gas may be collecting inside the chamber before lighting (delayed ignition). If you hear high-pitched whistling or screeching like a tea kettle, water is boiling inside restricted heating tubes due to severe chemical scaling or low flow.

Finally, inspect the bottom of the heater cabinet for water puddles while the pump runs. Water leaking inside the cabinet can drip onto burners, corroding the metal and disrupting clean combustion. Dripping water also damages expensive electronic circuit boards. If your heater leaks water internally, shows rollout damage, or repeatedly locks out with gas odors, stop operating the unit and contact a licensed pool service technician or certified gas professional for repairs.