Pool Heater Will Not Ignite? Work the Start Sequence
Most no-ignition calls we run in Arlington are not actually the heater. A gas heater refuses to light when any one of its safety checks fails, and the one that fails most often is water flow — which means the real fault is usually at the pump or the filter.
Work the start sequence in order and you will normally find it without guessing.
If you smell gas, stop here
Leave it alone, keep ignition sources away, and call the gas utility from somewhere else. Do not keep pressing the button to see if it catches. And whatever a forum tells you, never jumper out a pressure switch or a high limit to force a heater to fire — those safeties are what stand between a flow problem and a cracked heat exchanger or worse.
How a gas heater actually starts
Knowing the order is most of the diagnosis. The heater gets a call for heat from the thermostat, then confirms adequate water flow through the pressure switch. Only then does it energize the igniter, open the gas valve, and look for a flame on the sensor. If the sensor does not confirm flame within a few seconds, it shuts the gas off and locks out.
Every failure mode below is one of those steps not completing.
Cause 1: not enough water flow
The most common by a long way. The pressure switch is doing its job — it is refusing to let gas burn against a heat exchanger that does not have enough water moving through it. Fix the flow and the heater is usually fine.
What to check, in order
Water level at mid-skimmer. Skimmer and pump baskets empty. Filter pressure at or near its clean baseline rather than 10 psi over. Every valve fully open, including anything a spa diverter touches. A heater that fires and then cuts out after a minute or two is almost always this.
If the filter is the restriction, see pool filter pressure too high. If the pump is struggling to move water at all, start with a pump that will not prime.
Cause 2: no gas reaching it
Obvious once you check it, easy to assume. Confirm the gas shutoff at the heater is open, and that other gas appliances in the house are working — if the water heater and the range are fine, supply is probably fine. On propane, check the tank before anything else.
A heater that has been sitting unused all summer can also have air in the line and may need a few cycles to purge it before it catches.
Cause 3: the igniter has failed
Igniters are a wear part. If you can hear the unit go through its sequence and the gas valve click, but nothing lights, a dead igniter is the likely answer. On a hot-surface igniter you can sometimes see it is cracked. They are a routine replacement and among the cheaper heater repairs.
Cause 4: a fouled flame sensor
This one has a signature: the heater lights, runs for a few seconds, then shuts down and locks out, every time. The burner is lighting fine but the sensor cannot confirm it through a coating of soot or oxide, so the control assumes failure and closes the gas.
Cleaning a flame sensor is straightforward for a technician and does not need parts, which makes it one of the better outcomes on this list.
Cause 5: something has moved in
Worth saying because it is genuinely common here and almost never mentioned online. Pool heaters in North Texas sit unused from roughly May to October, and that is long enough for wasps, ants and the occasional rodent to nest in a burner tray or block a flue.
A heater that worked fine in spring and will not light on the first cold night in November is a strong candidate. It is also why the first fire of the season is worth doing before you actually need the heat.
What the error code is telling you
Codes differ between Pentair, Raypak, Jandy and Hayward, but they cluster into the same few families. A flow or pressure-switch code points at the pump and filter, not the heater. An ignition-lockout code means it tried and failed to prove flame — igniter, gas or flame sensor. A high-limit code means it got too hot, which is usually low flow again.
Note the exact code and the brand before you call. It genuinely shortens the visit.
What it costs to fix in Arlington
If the fault turns out to be flow, the fix is often a filter clean or a pump repair rather than heater work at all. Flame sensor cleaning needs no parts. Igniters, pressure switches and gas valves are individual components and are normally worth replacing. A cracked heat exchanger on a heater past about ten years is the point where replacement usually makes more sense, and we will tell you that plainly rather than selling you a repair that does not pay off.
Our service call is $149, it covers the full diagnosis, and it comes off the repair price if you go ahead. Every repair carries a one-year warranty. See pool heater repair for gas heaters and heat pumps, or equipment repair if the problem is upstream at the filter or the valves.
Before next season
Fire the heater once in early autumn, before the first cold snap, while a failure is an inconvenience rather than a problem. Keep the area around the unit clear so it can draw air, and look inside the cabinet for nests after the idle months. Keep the filter clean, because most heater lockouts here start as a flow problem somewhere else entirely.
Pool Pros — Family-owned pool service in Arlington, TX since 2005. Call 682-399-2593 for a free estimate.