Most pool heaters that won’t turn on have a simple cause: no power, the heater off or set too low, automation in the wrong mode, or not enough water flow. Work through those checks in order before you call for repair. If you smell gas, stop, shut off the gas and call your gas utility.
Call or text Steven: (832) 447-4236
Safety first
A gas heater burns fuel right next to your pool equipment. If you smell gas near the equipment pad, do not try to light anything or flip switches at the pad. Turn the gas off at the shutoff valve if you can do it safely. Move away from the area and call your gas utility. Wait until they clear it before anyone touches the heater.
Do not open heater panels. Behind them are high-voltage wiring, the gas valve and the ignition system. Everything in this guide can be done from the outside of the equipment, at the breaker, or at the control panel.
Checks you can safely do, in order
Go top to bottom. The simple causes come first.
1. Power, breaker and GFCI
Check the breaker for the heater and the pool equipment. A tripped breaker sits in the middle position. Flip it fully off, then back on. Many pads also have a GFCI outlet or breaker with a test and reset button. Press reset. If a breaker or GFCI trips again right away, leave it off. That points to an electrical fault, and it needs a technician.
2. Heater switched on and set above the water temperature
It sounds obvious, but it is a common cause. Make sure the heater is in pool or spa heat mode, not off or standby. Then check the set point. The heater will only fire if the set point is higher than the current water temperature. Raise it above the water temperature and give the heater time to start.
3. Automation and spa mode
If you have an automation system, it usually controls the heater. The heater’s own buttons may do nothing. Open the app or the indoor panel. Confirm heat is enabled for the body of water you want and that a schedule or remote setting isn’t overriding it. On pool and spa combos, check that the valves have actually switched to spa mode. If the system seems confused, our pool automation page covers what we can sort out.
4. Pump running and filter clean
Heaters need steady water flow. Low flow trips a safety switch, and the heater will not fire. Make sure the pump is running and the pump basket is empty. Check the filter pressure gauge. If pressure is higher than normal, the filter is likely dirty. In fall, oak leaves and pine needles load up baskets and filters. Our guide to pool filter cleaning walks through it.
Pump speed matters too. Federal pool pump efficiency standards took effect in 2021, and for most in-ground pools they effectively require variable-speed motors, according to the Appliance Standards Awareness Project. Those pumps save energy, but a speed set too low may not move enough water for the heater. Try a higher speed while heating.
5. Valves
Look at the valves around the pad. A valve turned the wrong way can starve the heater of flow or send water around it. If someone recently worked on the pad or switched to spa, check that the handles are where they normally sit.
6. Gas supply on
For gas heaters, confirm the gas valve to the heater is open. On a typical quarter-turn valve, the handle runs in line with the pipe when it is open. If other gas appliances in the house aren’t working either, the issue is upstream. Call your gas utility.
7. Heat pumps and cold air
Heat pumps pull heat from the air, so they need good airflow and enough warmth outside. Keep leaves and debris clear of the coil and fan. Hayward’s knowledge base says its heat pumps work in about 45-50°F air and cut off when the air drops below 50°F. On a cold morning, a Hayward heat pump that won’t run may be doing what it was designed to do.
Notes for Pentair, Hayward and Jandy heaters
All three brands work on the same basic idea. They need power, a call for heat, good water flow, and either gas and ignition or, for heat pumps, airflow. Their safety systems shut the heater down when something is off.
- Pentair: often paired with Pentair automation, so check the automation before the heater itself.
- Hayward: makes both gas heaters and heat pumps. Keep the cold-air cutoff in mind for heat pumps.
- Jandy: often run through AquaLink automation. Confirm heat is enabled there.
On any brand, the display may show a code. Don’t guess at it. Write it down for the technician. It helps with the diagnosis. More brand detail is on our Pentair, Hayward and Jandy heater repair page.
Jandy heater install
A close-up of an installed Jandy pool heater.
Heater and equipment repair
Pool heater and equipment repair work in The Woodlands, TX.
Dirty filter grids
Dirty DE filter grids before cleaning.
What needs a pro
If the simple checks don’t fix it, the fault is usually inside the heater. These jobs are for a technician:
- Ignition problems, when the heater clicks or tries to start but never lights
- Gas valve faults
- Temperature sensors giving bad readings
- Safety switches, including pressure and high-limit switches that keep tripping
- Heat exchanger problems, including scale buildup or damage
- Water or gas leaks at or inside the heater
- Breakers or GFCIs that trip again after reset
We repair gas heaters and heat pumps in-house as part of our pool heater repair service. We also watch the equipment on weekly visits to spot problems early. At Woodson’s Reserve in Spring we handle weekly saltwater service on a pool with an AquaCal heat pump and Pentair automation.
Repair or replace
Many heater problems are worth fixing. A failed sensor, switch or ignition part on a heater in good shape is a normal repair. Replacement makes more sense when several of these are true:
- The heat exchanger is leaking or badly damaged
- The cabinet and internals are heavily corroded
- The heater keeps failing, one part after another
- Parts are hard to find for that unit
Steven will tell you plainly which way he would go and why. If replacement is the better call, we install new equipment and match it to your pump, filter and automation. We handle heater calls along with our pool service in Spring, TX, plus pool service in The Woodlands and pool service in Conroe.
Common Questions
Why is my pool heater not turning on but the pump is running?
A running pump doesn’t always mean enough flow. A dirty filter, full baskets, a valve turned the wrong way, or a variable-speed pump set too low can trip the heater’s flow safety switch. Also check that the heater is on, the set point is above the water temperature, and your automation has heat enabled for the pool or spa.
Why won’t my pool heat pump work when it’s cold outside?
Heat pumps pull heat from the air, so cold air limits them. Hayward’s knowledge base says its heat pumps work in about 45-50°F air and cut off when the air drops below 50°F. For a Hayward heat pump on a cold morning, that shutdown is normal. Keep the coil and fan clear of leaves so airflow stays good.
What should I do if I smell gas near my pool heater?
Stop and don’t flip any switches or try to light the heater. If you can do it safely, turn off the gas at the shutoff valve. Move away from the equipment and call your gas utility. Don’t open heater panels. Once the utility clears it, have a technician inspect the heater before using it again.
Is it worth repairing an old pool heater or should I replace it?
Many repairs are worth it if the heater is otherwise in good shape. Sensors, switches and ignition parts are normal fixes. Replacement makes more sense when the heat exchanger leaks, the unit is heavily corroded, it keeps failing one part after another, or parts are hard to find. We’ll explain which option fits your equipment.
Can a dirty pool filter stop my heater from turning on?
Yes. Heaters need steady water flow, and a clogged filter cuts it. When flow drops, a safety switch keeps the heater from firing. Check your filter pressure gauge. If it’s higher than normal, the filter needs cleaning. Empty the skimmer and pump baskets too, especially in fall when leaves and pine needles pile up.
Owner-operated from E Benders Landing Blvd in Spring, 4.9 stars across 135+ Google reviews, no contracts. Serving Spring (77386, 77385), The Woodlands (77381) and Conroe. Request a free quote.
Call or text Steven: (832) 447-4236