How to Reset a Hayward Pool Heater

Resetting Your Heater from the Keypad and Electrical Breaker

Most modern Hayward heaters, such as the Universal H-Series, run on a digital control board that tracks water flow, temperature, and combustion. When something interrupts normal operation, the system triggers an automatic safety shutoff (often called a lockout) to prevent damage. You can usually clear this state directly from the front display.

The quickest way to clear a temporary glitch is through the buttons on your control pad. Follow these steps to restart the system from the front panel:

1. Find the MODE button on the front control pad faceplate (often called the bezel).
2. Press the MODE button until the display screen switches to STANDBY or OFF.
3. Wait at least 30 seconds to let the internal fan complete its post-purge cycle and allow the controls to rest.
4. Press the MODE button again to switch the unit back into POOL or SPA mode.
5. Use the UP arrow button to raise the set temperature at least two degrees above your current pool water temperature so the heater actively calls for heat.

If the display continues to flash an error code or freezes completely, the control board may need a hard reboot. Just like a home internet router, the digital circuit board inside the heater holds residual power in its small capacitors. A quick tap of the power button will not clear deep software hiccups or stubborn fault codes.

To perform a full electrical reboot, turn off the heater at the breaker (the main electrical switch in your fuse box):

1. Press the MODE button on the heater keypad until the screen shows STANDBY.
2. Walk over to your pool equipment electrical subpanel or your home electrical service panel.
3. Find the dedicated circuit breaker switch labeled for your pool heater.
4. Flip that breaker switch firmly to the full OFF position.
5. Leave the power switched off for a full 60 seconds so the internal electronics drain completely.
6. Flip the breaker switch back to ON, return to the heater, and select POOL mode on the keypad.

Once you restore power, the heater will run a brief system self-check. You will usually hear the exhaust blower fan spin up for 10 to 15 seconds before the gas valve clicks open and the spark igniter fires. If the display lights up and stays in normal operating mode, your reset worked.

Locating and Pressing the Internal Manual Reset Button

Not every shutdown comes from a digital glitch. If your heater got too hot during its last run, an overheating safety switch (often called a high-limit switch) will trip physically. This small sensor sits right against the water pipes inside the cabinet to stop the burners before scalding water damages your pool plumbing.

When this safety switch trips, the keypad cannot restart the heater until the physical switch clicks back into place. Some Hayward models use automatic switches that reset on their own once the metal cools down, but many units feature a manual button that requires a physical push.

Before you open the heater cabinet, put safety first. Always flip the breaker switch to OFF at your electrical panel, and turn the external gas supply shutoff valve to the closed position. Working inside an energized heater cabinet exposes you to high electrical voltage and hot metal surfaces.

After cutting all power, use a standard screwdriver to remove the screws securing the front service access door. Set the door panel aside on a flat patch of grass. Look toward the upper right side of the heater interior, right around the header where the cold pool water enters and hot water exits.

Look for a round safety disc mounted directly to the pipe or brass header, typically connected to two thin wires. In the center of this disc, you will find a small, raised button, which is usually red or black. If the heater overheated, that center pin will have popped outward slightly.

Gently press the pin inward with your fingertip. If the switch had tripped, you will feel a distinct mechanical click as it re-engages. If the button feels mushy or refuses to move, the switch has either cooled down and reset itself, or the high-heat sensor was never the reason your heater turned off. Replace the front door panel, tighten the screws, restore power at the breaker, and try starting the heater again.

What to Check Before You Try Restarting the Heater

Pool heaters require a steady, strong river of water running through them to pull heat away from the firebox. If the water slows down to a trickle, the water flow sensor (known as a pressure switch) immediately cuts off the gas supply. Resetting your heater over and over without checking your water flow will only cause the unit to shut down seconds later.

Before you cycle the power switches again, run through this basic maintenance checklist to make sure your pool system can actually support the heater:

• Pump strainer basket: Turn off your pool pump, open the clear pump lid, and dump out any leaves, pine needles, or debris that could choke the intake.
• Skimmer baskets: Empty out all pool skimmer baskets so surface water flows into your suction pipes without restriction.
• Filter pressure gauge: Look at the pressure dial on top of your pool filter tank. If the reading sits 8 to 10 pounds above your clean baseline pressure, backwash the sand or clean the filter cartridges before heating.
• Plumbing bypass valves: Inspect every valve handle on your equipment pad to ensure water is routed fully through the heater rather than diverted down a waste line or bypass loop.
• Pool water level: Confirm the water level in the pool reaches at least halfway up the skimmer mouth so your pump does not suck air bubbles into the lines.

Suction problems frequently trace back to how water circulates through your system. If you plumbed your own pool pad or decided to install an inground pool kit yourself, you already know that straight pipe runs and clear suction lines keep water pressure steady. If an automatic suction pool cleaner gets packed with leaves or pinches off an intake line, that sudden drop in water volume will trigger the heater safety shutoff right away.

Always turn on your pool pump first and let it run on high speed for at least two full minutes before turning on the heater. Look through the pump lid to ensure the pump pot is completely full of water with no swirling air pockets. Once your circulation runs clear and strong, your heater has the water flow it needs to run safely.

Why Resets Fail and When to Call a Professional

If you cycle the keypad and flip the breaker, but the heater shuts down again within a minute, the unit is doing its job by protecting itself. Understanding the letters on the screen tells you which part of the system is failing.

A frequent message is the "LO" fault code. This code indicates low water flow. When you see this code, the internal water flow sensor cannot detect enough water pressure to close its electrical contacts. If your filter is clean and your pump runs strong, the thin copper tube leading to the water pressure switch might be clogged with mineral scale or debris.

Another common message is the "IF" code, which stands for ignition failure. Hayward heaters attempt to light the gas burner three consecutive times before locking themselves out. If your gas tank is low, if the manual gas valve on the pipe remains shut, or if small spiders have built nests inside the burner orifices, the heater cannot maintain a flame. Resetting the keypad will only restart the three-try cycle without solving the fuel supply issue.

You might also see an "AO" or "AC" code, which points to a blower vacuum switch or air passage problem. Gas heaters use an internal fan to blow exhaust gases outdoors safely. If wind pushes down the exhaust chimney, if leaves blow into the top vent, or if the vacuum switch fails to sense air movement, the control board stops the ignition cycle instantly.

While resetting a digital code is simple and safe, some warning signs mean you should stop troubleshooting immediately:

• Smell of gas: If you smell rotten eggs or raw gas near the equipment pad, do not touch the electrical switches or keypad. Shut off the main gas valve on the pipe, walk away, and call your gas supplier or fire department.
• Loud banging or whistling: Banging sounds (often called kettling) mean trapped water is boiling into steam inside the heat exchanger. Turn off the heater right away to prevent ruptured plumbing.
• Soot or black smoke: Heavy black smoke or soot marks on the top exhaust panel point to improper gas combustion or a clogged burner tray, which requires professional cleaning.
• Repeated trips within five minutes: If you perform two complete resets and the heater trips a third time, leave the breaker off. Forcing the unit to restart can burn out internal control boards or melt electrical harnesses.

When basic cleaning, water flow checks, and a breaker power cycle do not resolve the issue, contact a licensed gas technician or an authorized pool equipment repair service. Certified technicians have the diagnostic tools needed to test electrical millivolts, inspect gas line pressure, and replace failed safety switches without putting your equipment or home at risk.

FAQs

Why does my Hayward heater say "LO" right after I reset it?

The "LO" code indicates low water flow through the heater cabinet. The water flow sensor inside the unit cannot detect enough water pressure to safely light the gas burners. Clean your pool filter, empty the pump and skimmer baskets, and verify your pool pump is running at full speed to resolve the code.

Can I reset my pool heater while the pool pump is turned off?

You should never try to start or reset your pool heater while the pump is turned off. Hayward heaters need steady water movement to cool internal metal coils and close the water pressure switch. Always turn your pool pump on first, confirm strong water circulation, and then turn on the heater.

How long should I wait between reset attempts?

Wait at least two to three minutes between keypad resets to allow the exhaust fan to clear out unburnt gas and let internal sensors settle. If you turn off power at the main breaker, leave the switch off for at least 60 seconds before flipping it back on. If the heater fails after three consecutive reset attempts, stop resetting it and inspect your water flow or call a technician.