Direct answer
If the panel is on and jets and lights work, but the water isn’t warming up, Hot Spring documents this exact scenario as caused by an open pressure switch, a tripped circulation-pump thermal cut-off, or an air lock from a recent refill (Hot Spring). All three are protective responses to a flow problem, not necessarily a sign that the heating element itself is broken.
Safety note
Do not open the control box or touch wiring. Do not bypass a pressure switch, flow switch, or thermal cut-off. If a breaker or GFCI is involved, reset it once only if your manual permits it — if it will not reset, or trips again, stop and contact qualified service. These are homeowner observation and cleaning checks only, not electrical diagnosis.
Why this looks different from “no power at all”
Hot Spring’s troubleshooting chart lists a completely inoperative spa (dark panel, nothing responding) as a separate case, pointing to a power failure, a tripped GFCI, or a tripped heater high-limit thermostat (Hot Spring). Power-but-no-heat is different: the electronics are clearly getting power, so Hot Spring’s guidance points instead to a safety device that reacts to water flow rather than to electricity. The chart lists this scenario separately, with the blinking “Ready” and “Power” logo lights called out as a visible sign (Hot Spring).
Confirming which case you’re in first can save time: rechecking the breaker panel won’t help if the real issue is a clogged filter, and cleaning the filter won’t help if the spa genuinely has no power. Look at the panel and jets together before starting any check, so you know which set of causes actually applies to your situation.
The three causes Hot Spring lists for this exact scenario
An open pressure switch
A pressure switch is designed to confirm water is flowing before allowing the heater to run. Hot Spring’s guidance is to check for clogged filters, noting the switch should reset on its own once flow through the heater is restored (Hot Spring). See Can a Dirty Filter Stop a Hot Tub From Heating? for the filter-check steps.
A tripped circulation-pump thermal cut-off
This protects the circulation pump from overheating. Hot Spring recommends checking for clogged filters and air locks in the plumbing, then disconnecting power so the pump can cool — the cut-off should reset on its own once the pump has cooled and power is reconnected (Hot Spring).
An air lock from a recent refill
If the spa was filled or topped off recently, trapped air can block proper flow to the heater. Hot Spring’s fix is to run water down the main filter in the filter compartment to push the air lock out (Hot Spring). See How to Tell if a Hot Tub Has an Air Lock if you’re not sure this applies to you.
Safe checks the homeowner can do
- Confirm the panel, jets, and lights are genuinely all working. This is what separates this scenario from a full power failure.
- Check the filter for visible clogging and clean it following your manual’s method.
- Check the water level against your manual’s fill line — Jacuzzi notes low water can also starve flow and trigger a protective shutdown.
- If you refilled the spa recently, follow your manual’s air-lock or fill-through-filter procedure.
- If flow looks restored, turn the spa off at the breaker or disconnect, wait, then restore power so a tripped thermal cut-off has a chance to reset, following your manual’s guidance on how long to wait.
- Watch for the same indicator light or blinking pattern to clear once these steps are complete.
When to stop and call a technician
- Filter cleaning, water-level correction, and an air-lock check don’t restore heat
- The same pressure-switch or thermal-cut-off indicator keeps returning
- The GFCI or breaker won’t reset, or trips again after one attempt
- You suspect the heating element or another internal component has failed
- You would need to open the control box, test wiring, or bypass a safety device to keep going
If you’ve worked through the flow-related causes above and heat still hasn’t returned, that’s the point to stop rather than continue guessing.
For the full first-checks routine covering both “no power” and “power but no heat,” see Hot Tub Not Heating: What to Check First.