Home / Services / Pool Heater Repair
Gas Fitting · Pool HeatersPool Heater Repair
Pool heater repair on a gas heater that will not fire usually traces to water flow, not gas: a dirty filter or a closed valve drops the flow, the pressure switch stays open, and the heater refuses to light by design. After that come a failed igniter and wiring chewed by mice over the winter. A diagnostic visit is $90–$150, and you get the repair price in writing before parts are ordered.
Check the water side before you call. Every gas pool heater has a pressure or flow switch that proves water is moving through the heat exchanger before the gas valve may open, and a filter due for a backwash, a full pump basket, a low water level or a bypass left open after winterizing will hold that switch open. Clean the filter, empty the baskets, confirm the pump is primed and try again. A flow fault that persists with strong flow at the returns points to the switch or its tubing.
With flow proven, ignition is next. The igniter is a fragile element that cracks with age: the fan runs, the burner never lights and the heater locks out after several tries, whereas a flame sensor coated with oxide lets the burner light and then drops it within seconds. Spring adds causes of its own, because the cabinet is a dry, sheltered box all winter. Mice nest on the burner tray and chew the low-voltage harness, and spiders spin webs in the burner orifices, which block gas and cause delayed, rough ignition.
The expensive failures are in the heat exchanger, and both are preventable. Water chemistry causes the first: pH held below about 7.2, or chlorine tablets dissolving in the skimmer with the pump off, sends acidic water through the copper tubes and thins them until they leak, and blue-green stains on the pool finish are the dissolved copper. Combustion causes the second: low gas pressure from an undersized line or a failing regulator gives a lazy yellow flame that lays soot on the fins, the soot blocks the flue passages, and the heater overheats and makes carbon monoxide. Soot on top of the cabinet means stop using it and call.
Whether to repair depends on which part and how old. Igniters, sensors, pressure switches, limit switches, harness repairs and burner cleaning are routine on a heater of any age. A leaking heat exchanger on a heater past ten seasons is usually the end, since it is the costliest part in the cabinet and everything around it has had the same weather. When sooting comes from the gas supply, the fix is a gas line upgrade, not a heater part, and when replacement is the answer the next page is pool heater installation.
Check first, call, or shut it off
- Check first: filter backwashed, pump and skimmer baskets empty, valves open, water level at mid-skimmer
- Call: the heater clicks or its fan runs but the burner never lights, even with good water flow
- Call: the burner lights, runs a few seconds and shuts off, over and over
- Shut it off and call: black soot on the cabinet or vent, or a yellow, lifting flame
- Shut it off and call: water dripping inside the cabinet with the pump running and the heater off
How it works
Filter pressure, pump prime, valve positions and the pressure switch are checked before any gas component, because many no-fire calls end there.
Igniter resistance, flame signal, gas pressure at the inlet and the manifold with the heater firing, and a look at the burners and exchanger fins for soot, webs and nests.
Part replaced or burners and exchanger cleaned, harness repaired, then the heater is run through several cycles and the temperature rise across it measured. Book a pool heater diagnostic.
Common questions
What gets checked at spring start-up before the first fire?
The cabinet is opened and cleared of nests, chewed wires and debris on the burners. Winterizing plugs and drain fittings go back in, the bypass is set, and the pump runs at full flow before the heater is switched on. Then the gas is turned on, the union and valve are leak-tested with solution, and the first ignition and flame are watched.
Why does my pool heater shut off after a few minutes?
Usually the high-limit switch is opening because the heat exchanger is too hot: low water flow, a stuck internal bypass, scale inside the tubes or soot on the outside. A dirty flame sensor shuts it down in seconds, not minutes. Note how long it runs and any code on the display, because that timing narrows the cause before the visit.
Is soot on my pool heater dangerous?
Yes. Soot means incomplete combustion, and incomplete combustion makes carbon monoxide. Outdoors it disperses, but a heater near a window, a door or under an overhang can send it inside, and a sooted exchanger overheats. Shut the heater off at its switch and its gas valve, and have the gas pressure and burners checked before it runs again.
What water chemistry protects the heater?
Keep pH between 7.2 and 7.8 and total alkalinity in the range your pool supplier recommends, and never leave chlorine tablets in the skimmer, where they feed concentrated acid straight to the heater when the pump restarts. With hard fill water, high calcium also scales the tubes from the inside. Test weekly, and check what your heater's warranty says about chemistry damage.
I smell gas near the pool heater. What do I do?
Close the heater's gas valve if you can reach it safely, keep people and ignition sources away from the pad, and call from a distance. Outdoor leaks often come from a union or connector disturbed during winterizing. The full steps are in what to do if you smell gas, and our line is answered around the clock.