Most “my heater is broken” calls resolve in the first 15 minutes of the visit. The trick is having a repeatable diagnostic sequence. This is the one we work through on every no-heat call before we start pulling parts.
What's yours and what's ours: the five checks below are yours to do from outside the heater. The two symptom tables show what a tech does with the cabinet open, so read them for context, not as a to-do list. Gas, electrical, and refrigerant work stay with a licensed tech.
The universal first five checks
- Is the pump running and delivering flow?Almost every heater has a pressure or flow switch that refuses to fire without circulation. The most common “heater fault” is actually a dirty filter, a closed valve, or a skimmer basket full of leaves.
- Is the thermostat set above pool temp? A laughable number of calls end here. Guests dial it down; shared controls get bumped; the setting resets after a power blip on some models.
- Is the bypass open on solar or a heat-recovery loop? If flow is being diverted away from the heater you get cold water and a confused heater.
- Fault code on the display? Read it before you touch anything. Manufacturers publish code tables; most techs have them bookmarked on their phone.
- Fireman switch or remote enable?If the heater is time-clocked or controller-driven and the schedule isn't calling for heat, the heater won't fire no matter how hot the thermostat wants it.
Gas heater: specific failures by symptom
| Symptom | Likely cause | First check |
|---|---|---|
| Clicks, no ignition | No gas, pilot out, blown igniter | Confirm the gas valve outside the heater is open. A tech inspects the igniter. |
| Lights, runs briefly, faults out | Pressure switch, flame sensor, air switch | A tech checks the flame sensor and measures switch continuity. |
| Sooty flame or yellow color | Dirty burners, wasp nest, low gas pressure | A tech cleans the burner tray and tests inlet pressure. |
| Loud rumble or boom on ignition | Delayed ignition from dirty burners or weak spark | Shut down and service immediately — safety risk. |
| Runs but heats slowly | Scaled heat exchanger, undersized gas line | A tech tests inlet gas pressure; schedule a descale. |
Heat pump: specific failures by symptom
| Symptom | Likely cause | First check |
|---|---|---|
| Fan runs, no heat | Low refrigerant, bad reversing valve, compressor off | A tech listens for the compressor and amp-clamps the leads. |
| Nothing runs | Blown capacitor, tripped breaker, bad contactor | Check the breaker; a tech tests the capacitor and contactor. |
| Ice on the coil | Low ambient, low refrigerant, stuck reversing valve | If ambient <50°F this may be normal defrost cycle. |
| Water puddle under unit | Normal condensate or heat-exchanger leak | Catch water dripping from the unit itself (not the puddle) and dip a chlorine test strip in it: no chlorine means condensation; chlorine means pool water and a likely exchanger leak. See heater leaking or noisy. |
| Loud compressor rattle | Worn bearings or grounding-out | Shut down; refrigerant work is licensed-tech territory. |
When to stop troubleshooting and call a specialist
- Gas smell.Don't touch the heater or nearby switches: shut off the gas if you safely can, leave the area, and call your gas utility. Never test for a gas leak with a flame or an ignition source.
- Refrigerant and electrical work.Heat-pump refrigerant is a licensed-technician task (EPA Section 608), and capacitor and contactor work is a tech's job too.
- Cracked heat exchanger. Pool water getting into the combustion side of a gas heater eats the exchanger fast. Diagnose by pressure test; replace, not repair.
Most heater calls come down to a dirty filter, a tripped breaker, or a bumped thermostat. Work the simple list first. The hard problems are real, but they're rare.
Frequently asked questions
Five things, in this order. Is the pump running and delivering flow — almost every heater has a pressure or flow switch that refuses to fire without circulation, and a dirty filter, closed valve, or leaf-packed skimmer basket is the single most common cause of a supposed heater fault. Is the thermostat set above pool temperature. Is a solar or heat-recovery bypass diverting flow away from the heater. Is there a fault code on the display, which you should read before touching anything. And is the fireman switch or remote enable actually calling for heat.
Clicking with no ignition points at no gas, a pilot that is out, or a blown igniter. Confirm the gas valve is open, then inspect the igniter visually for cracks. If it lights, runs briefly, then faults out instead, look at the pressure switch, flame sensor, and air switch — check flame-sensor cleanliness first, then measure switch continuity.
That is delayed ignition, caused by dirty burners or a weak spark letting gas accumulate before it catches. Shut the heater down and have it serviced immediately — this one is a genuine safety issue, not a performance complaint, and it is the one symptom on the list that should not wait.
Fan running with no heat points at low refrigerant, a bad reversing valve, or a compressor that is not actually running. A tech listens for the compressor and amp-clamps its leads to confirm. If nothing runs at all, look instead at a blown capacitor, a tripped breaker, or a bad contactor — check the breaker, and leave the capacitor and contactor to a tech. Refrigerant work itself is licensed work and is not a homeowner job.
Usually a scaled heat exchanger or an undersized gas line. Both restrict the heater's ability to transfer or receive energy even though it fires normally. The diagnosis is an inlet gas-pressure test plus a look at the exchanger; the fix is a descale, a gas-line correction, or both. Slow heating is also the symptom most often misread as "the heater is just old".
Worked the checks and it still won't fire?
Nine times out of ten a heater that won't fire is starved, not broken — but if flow is good and the code is still there, we diagnose Pentair, Hayward, Raypak and AquaCal across Palm Beach and Broward. Quoted in writing before any part is ordered.