A pool heater is the most sensitive piece of equipment on the pad: it will not light without enough water flowing through it, it shuts itself down the moment a sensor dislikes something, and it tells you why in a language most owners have never been taught. Before you book a repair, work through this list from the top. Most of it takes a screwdriver and a flashlight, and the order matters, because the heater checks these things in the same order you should.
First, the things that are not the heater
Filter pressure. A dirty filter is the number one reason a heater refuses to light. The heater has a pressure or flow switch that must see enough water moving before the burner is allowed to fire; a clogged filter, a full pump basket or a full skimmer basket starves it. Check the gauge against the clean pressure you wrote down (or the mark on the gauge), backwash or clean the cartridge, empty the baskets.
Water level and valves. Water below mid-skimmer lets the pump pull air, flow drops, the heater drops out. Then look at every valve on the pad: a heater bypass left open after a repair, a return valve half closed, a three-way valve turned the wrong way after a spa-mode swap. The heater cannot light if the water is going around it.
Is anything asking for heat? The thermostat has to be set above the current water temperature, the mode has to be on (pool, spa, or both), and if an automation system or timer runs the pad, it has to be calling for heat right now. A heater that is "off" because the schedule says so looks exactly like a dead heater.
Fuel and power. Gas valve on the supply line open (handle in line with the pipe), propane tank not empty, the heater's own power switch on, the breaker not tripped, the service switch inside the door in the right position. Heat pumps: the breaker and the disconnect, and air temperature above the unit's minimum.
Then, what the heater is doing
| What you see | What it usually means | Your move |
|---|---|---|
| Clicks, tries to light, quits | Ignition failure: the igniter is not lighting the gas, or the flame sensor is not seeing the flame. Dirty burner tray, failed igniter, gas pressure. | Rule out gas supply and flow; if it still clicks and quits, call. Igniters and sensors are a one-visit repair. |
| Fires, runs a few minutes, shuts off, repeats | Short cycling: low flow tripping the pressure switch, or the high-limit switch tripping because water in the exchanger is getting too hot for lack of flow. | Filter, baskets, water level, valves. If flow is good and it still cycles, a sensor, the switch or the board. |
| Runs and runs, pool never warms | The heater is fine; the setup is not. Undersized for the pool, bypass set wrong, heat pump in cold air, no cover at night losing the heat as fast as it is made. | Cover the pool. If it still cannot keep up, the sizing needs a look. |
| Water under the heater | Condensation on a cool morning (a small puddle that dries) is normal. A steady drip is the heat exchanger or header: bad water chemistry or freeze damage. | Dry puddle by noon: ignore. Wet pad every day: shut it down and call; this one gets worse. |
| Soot, black marks, yellow lazy flame, smell | Combustion or venting problem. | Turn the heater off and call. Do not keep running it. |
| Fan runs, no heat (heat pump) | Air too cold for the unit, a defrost cycle, or a refrigerant or compressor fault. | Check the air temperature against the unit's minimum; otherwise it is a technician's job. |
| Trips the breaker | Heat pumps: compressor or fan motor. Gas heaters: the blower, the transformer or wet wiring. | Leave it off and call. |
What the error messages mean
Every brand uses its own abbreviations, but they fall into four families. A flow or pressure message (often something like PS, LO FLO, or a pressure-switch light) means the heater is not seeing enough water: go back to the filter, baskets, level and valves. A high-limit or overheat message means the water inside got too hot, again almost always a flow problem. An ignition message means it tried to light and could not. A sensor message (thermistor, open or shorted sensor) is a failed part. Take a photo of the display or the blinking-light pattern and the label inside the door before you clear it; that photo saves a diagnostic visit.
When to stop and call
Any gas smell, any soot or discoloration, water leaking from the body of the heater, or a heater that keeps locking out after you have fixed the flow. Those are not owner jobs. The pool heater repair page lists what to have ready when you call (brand and model from the plate, a photo of the display, when it last worked and what changed); the service department works on Pentair, Hayward and the other major brands on inground pools across Omaha, Papillion, La Vista, Bellevue, Elkhorn, Gretna, Bennington and Council Bluffs, on the pools we built and the ones we did not.
Repair or replace?
A failed igniter, pressure switch, sensor or board on an otherwise sound heater is a repair, and most of those parts are on the truck or a day away. A leaking heat exchanger or a header cracked by a freeze is a replacement, and a replacement should be sized to the pool and to how you swim, not swapped like for like out of habit. Gas heater versus heat pump, sizing and what a new one needs from the gas line are on the heater page; the FAQ there covers running costs honestly.
How to not read this page again next year
- Keep the water balanced. Low pH and high chlorine eat heat exchangers from the inside. Free water testing at the counter, balancers on the shelf.
- Keep the flow up. Clean filter, empty baskets, water at mid-skimmer. Pump and filter parts are at the store if a lid o-ring or a gauge has given up.
- Drain it every fall. Water left inside a heater over a Nebraska winter cracks the header; the closing crew pulls the plugs and blows the lines as part of winterizing.
- Look at it every spring. A glance at the burner tray, the exchanger and the pressure switch at the opening catches most problems while they are small.
Hot tub heater instead? The same logic applies (flow first, then the element and the sensors), and it is its own page: hot tub repair in Omaha.
Frequently asked questions
Why does my pool heater click but not light?
The igniter is sparking (or glowing) but the gas is not lighting, or it lights and the flame sensor cannot see it. Check that the gas valve on the supply line is open and the propane tank is not empty; if those are fine, the burner tray, the igniter or the flame sensor needs a technician.
Can I run a pool heater with a dirty filter?
It will not let you for long. Low flow trips the pressure switch, and if the switch is fooled, the high-limit shuts the heater down to protect the exchanger. Clean the filter first; it fixes more heater complaints than any part does.
How long should a pool heater take to heat the pool?
A properly sized gas heater warms a typical backyard pool in hours, not days; a heat pump is slower and is built to hold a temperature rather than sprint to one. If the heater runs all day and the water barely moves, cover the pool at night and have the sizing checked.
Should I replace a pool heater that is over ten years old?
Not automatically. If the heat exchanger is sound and the fault is an igniter, switch, sensor or board, repair it. If the exchanger leaks or the header is freeze-cracked, replace it, and size the new one to the pool rather than copying the old label.
Is it the heater, or is the pool losing the heat?
An uncovered pool gives most of its heat back to the night air. If the heater reaches temperature by evening and the pool is cold again by morning, the heater is doing its job and a cover is the fix.
Do you repair pool heaters you didn't install?
Yes. Pentair, Hayward and the other major brands on inground pools across the Omaha metro, whether we built the pool or not. Details and what to have ready are on the pool heater repair page.