Extend Your Swimming Season! Troubleshooting a Gas Pool Heater

With summer coming to a close, pool owners are faced with the choice of closing up for the season or firing up their pool heaters to keep on swimming. But what happens when they try to turn on the heater and it does not work correctly? If you are a CPO® experienced and certified pool service technician, there are several ways to troubleshoot a malfunctioning gas pool heater. If you are not a certified service technician, you should hire a professional immediately.

Gas Pool Heater Safety

When handling any pool equipment, your top priority should always be safety. This is especially true when dealing with heaters. An essential safety tip is to make sure to never operate a heater if any part of it has been under water. In this situation, immediately call a certified service technician to inspect and repair the heater. If overheating starts to occur or the gas supply won’t shut off, immediately turn off the manual gas control valve.


Never keep any objects on top of a heater. This could block airflow and cause damage or it could create a fire hazard. Finally, do not touch any surface of the heater while it is in operation, as it can be extremely hot. The addition of a vent cap can help reduce the surface temperature of a heater, but it should still never be touched.

Heater Won’t Ignite

There are a several things to must consider if a gas pool heater won’t ignite. First, is the system switch on? Is the thermostat up to the correct temperature? Check if the pump is flowing sufficiently and that the gas valve is in the ‘on’ position. Is the gas supply valve open? Ensure that the pilot is lit and that all plumbing and filter valves are open. If you have addressed these steps and the heater still won’t ignite, call a service technician.

Pilot Light

When the pilot light on a heater is not working, it could be due to improper venting, a low gas pressure or insufficient air supply. If the pilot light works but needs to be constantly relit, look out for water runoff that could be extinguishing the flame. For further troubleshooting, contact a certified service technician.

Low Water Temperature

If a gas pool heater isn’t correctly regulating temperature, there are a few things to look out for. Check if the thermostat is set at the correct temperature and adjust it properly. There is also a possibility that low outside temperatures are causing heat loss. In this case, a solar cover can help slow down the head loss. If the heater completes its cycle before reaching the correct temperature, you could be dealing with a closed valve, dirty filter, inadequate water flow, reverse water connections or the pressure switch needs to be adjusted. It could also be possible that the thermostat is not calibrated correctly and needs replacement.

Leaking Water

If your heater is leaking water, it could be that a low pH has corroded the plumbing lines of the heat exchanger. It could also be caused by freezing damage to the plumbing. If the heater only leaks when the burner is lit, the cause could be condensation, a damaged bypass or excessive water flow from an oversized pump.

Black Exhaust and Heat Damage

Sometimes a heater may become black and discolored on top or the heater exhaust could be a darkened color. This is often due to low gas pressure or an inadequate air supply and venting. Either way, the heater must be inspected by a qualified service technician.

If the heater has heat damage resulting in a warped or buckled finish, there could be low gas pressure, a down-draft, improper air supply or a venting issue. If the heater is in a windy area or near a vertical wall, it may need a wind stack installed.


Learn From the Experts

Remember, this is just an outline of gas pool heater troubleshooting. Unless you are a certified pool technician, you should not try to service your heater. Your first step to becoming a certified pool technician should include a course in CPO® certification. Pool Operation Management offers award-winning, two-day courses in CPO® certification. We offer the perfect start to becoming a pool expert. We also offer residential and commercial pool maintenance services, so we can maintain your pool for you. Contact us today to get started.

*This information is obtained from the Certified Pool and Spa Operator Handbook. This information may not be applicable to your pool based on your pool type and location. One should reference all applicable regulations and standards for your facility.

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