Pool heaters are the divas of your equipment pad. When one little thing is off, they just refuse to perform. Here are some of the most common reasons a pool heater won’t work, starting with the easy stuff you can check right now:
Quick checks (do these first)
1. Is the heater actually getting power or gas?
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Gas heater: Ensure the gas valve is fully open and that other gas appliances are working.
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Electric/heat pump: Check the breaker and any nearby disconnect switch.
2. Is the thermostat set higher than the current water temp?
Sounds obvious, but heaters won’t turn on unless the set temp is higher than the pool water.
3. Is your circulation pump running?
Most heaters won’t fire unless water is flowing.
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Pump must be on
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Valves open
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No timers shutting it off early
Very common “silent killer” issues
4. Dirty or clogged filter
Low water flow = heater refuses to start.
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Check filter pressure
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Backwash or clean cartridges if pressure is high
5. Air or water flow problems
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Skimmer baskets full?
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Pump basket clogged?
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Valves partially closed?
If the heater tries but won’t stay on
6. Pressure switch or flow switch
If flow is borderline, the heater may:
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Start for a few seconds then shut of
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This often points to filtration or pump issues.
7. Ignition or flame failure (gas heaters)
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Clicking but no flame → ignition or gas issue
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Flame starts then shuts off → dirty burners, bad sensor, or gas pressure problem
Heat pump–specific problems
If it’s a heat pump:
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Outside air temp usually must be ~50°F+ (exact number will vary per model)
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If it is too cold outside, the unit will stop attempting to heat to protect itself from frosting over
When it’s likely a pro-level repair
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Heater shows error codes (check the owner's manual for code explanation and possible solutions)
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Strong gas smell
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Repeated ignition failures
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Unit is 10–15+ years old and never serviced
Final Thoughts
There are many factors outside your heater that can prevent it from working. A quick check of your pump, valves, and filter pressure may give you all the answers you need. If the issue seems more complex, it may be time to reach out to a pool professional. At PoolPartsToGo, we are happy to answer any questions that you may have.
Happy (warm) swimming!
