Equipment and field

Pool Heater Won't Fire? Checks and When to Stop

What to check when a gas pool heater will not fire, which checks are safe for a route tech, and when to stop and call a licensed gas or electrical pro.

A heater that will not fire is a common callback in cooler months and a frustrating one, because the cause can be as simple as a dirty filter or as serious as a gas problem. This page covers what a pool tech can safely check and exactly where to stop.

Stop rules first

Gas and electrical work carry real risk. Know these lines before you open a cabinet.

If you smell gas, stop everything. Do not turn switches on or off, do not light anything, and do not look for the leak. Leave the area. From a safe distance, call your gas utility's emergency line or 911. Keep people and pets away.

Call a licensed gas technician or the heater maker's authorized service for any of these:

• Anything on the gas supply side, including the valve, regulator, lines, or manifold
• The burner, igniter, flame sensor, gas valve, or control board
• Soot, scorch marks, melted wiring, or signs of flame rollout
• A blocked or damaged vent, flue, or heat exchanger
• Repeated lockouts after a single reset
• Anything you are not sure about

Call a licensed electrician if the breaker trips, wiring is damaged, or the heater cabinet has water inside. Rules on who can work on gas appliances and electrical systems vary by state and city, so check yours. This page is not a substitute for the manual or for a licensed professional.

What you can check

These checks do not require opening gas components.

1. Flow

Most heaters will not fire without enough water flow. Check:

• Pump is running and primed
• Filter pressure is not far above clean
• Skimmer and pump baskets are clear
• Valves on the heater loop are open, and any bypass valve is set the way the manual says
• Cleaner or spa valves are not stealing flow

A dirty filter is a frequent culprit. Clean it per the steps in cartridge, DE and sand filter cleaning.

2. Settings

• Heater switch is on
• Thermostat is set above the current water temperature
• Pool and spa mode are correct
• Timer or automation is not locking out the heater
• Remote controller or automation panel is not set to off

A customer or an automation schedule can turn off a heater without anyone noticing. Check this first, because it takes ten seconds.

3. Display or code

Read the display. Many heaters show a fault code or an LED sequence. Photograph the screen and the data plate, including the model and serial numbers. That photo is what a technician will ask for first.

You can usually reset a lockout once, following the manual. If the fault returns, stop.

4. Outside inspection

Look around the heater without removing any panel.

• Debris, leaves, or nests near the vent or air intake
• Spiders or insects around burner openings, which only a pro should address
• Evidence of leaks, rust, or white scale at fittings
• Anything stored against the heater, which blocks air

Keep combustible items and chemicals away from a gas heater. Never store chlorine, acid, or fuel next to it.

5. Water chemistry

Chemistry affects heaters over time. Low pH or aggressive water can corrode a heat exchanger, and hard, scaling water can coat it. Check the saturation index and keep pH in the 7.4 to 7.6 range. A copper heat exchanger turning the water blue-green points to corrosion. Talk to the customer about the cost of a repair.

Symptom table

Heat pumps

Heat pumps do not burn gas. They still have their own limits. They need air flow, a minimum outside temperature that depends on the unit, and water flow. A heat pump that ices over in cool weather may be in defrost, which is normal. Check the manual before you call it a fault. Refrigerant and electrical work belong to licensed techs.

Example

Say you arrive at a pool whose heater was working last week. The display shows a flow-related code. The filter pressure reads 22 psi when the clean reading is 14. You clean the filter, restart the pump, and press reset once. The heater fires.

Now change the scene. The display shows an ignition code, and a second reset gives the same code. You photograph the screen and data plate, turn the heater off, tell the customer it needs a licensed gas technician, and note it in the report. That is the right call, and it saves the customer from a warranty problem.

Mistakes to avoid

• Bypassing a safety switch. Never jumper or tape a pressure or flow switch.
• Resetting over and over. One reset is a test. Repeated resets hide a fault.
• Opening gas parts. Leave valves, burners, and igniters to licensed techs.
• Ignoring the filter. Check flow first, because it is the cheapest fix.
• Skipping the photo. The data plate and display photo save a second trip.

If you run a route, set a standing rule that gas work always goes to a licensed contractor, and keep a few names handy. See pool truck setup for the kit that makes these field checks quick.