Quick Answer: Before assuming a dead heater, reset the GFCI outlet or breaker — it trips silently and mimics total heater failure, and it costs nothing to check. The second most common cause is a clogged filter cartridge restricting flow, which trips the internal flow switch and shuts the heater off as a safety measure even when the element is fine. If both of those check out and the water still won’t climb in temperature after a full cycle, the heating element or PTC assembly itself has likely failed and needs replacing.
Last updated: August 5, 2026.
A hot tub that won’t heat is rarely a mystery once you work through it in order — but troubleshooting it backwards (assuming the worst and buying a new heater first) wastes money more often than it fixes anything. Here’s what actually stops a tub from heating, in the order to check it, on both inflatable and hard-shell spas.
Hot tub heating failures by the numbers
- 1-3°F per hour is the realistic heating rate for most inflatable and plug-and-play spas, according to manufacturer specs from Intex and Bestway — a tub that “isn’t heating” after 2 hours from a cold fill is often just on schedule, not broken.
- 42.8°F (6°C) is the exact ambient temperature at which Bestway’s FreezeShield feature triggers an automatic reheat cycle to protect the pump and lines, per Bestway’s owner’s manual — below that without freeze protection, a tub can stop heating because it’s fighting to avoid freezing, not because anything failed.
- A clogged filter cartridge restricting water flow is one of the most common reasons a functioning heater shuts itself off mid-cycle, since the internal flow switch is designed to cut heat rather than risk running an element dry.
Work through these in order
- Reset the GFCI. Every hot tub — 120V plug-and-play or 240V hardwired — runs through a GFCI outlet or breaker, and a trip looks exactly like a dead heater: no error, just no heat. Reset it once. See our hot tub wiring guide for where that GFCI actually lives on each tub type.
- Check the water level. Low water can sit below the intake and stop heating (and sometimes the pump) entirely, independent of any electrical fault. Top it off before troubleshooting further.
- Rinse or replace the filter. A dirty cartridge restricts flow enough to trip the internal flow switch, which shuts the heater off as a designed safety measure — this is genuinely one of the most common “dead heater” calls that isn’t actually a dead heater. Our hot tub filters guide covers how often to rinse versus replace.
- Confirm the setpoint and mode. It’s easy to bump the thermostat down or leave a tub in economy/sleep mode, which limits heating to scheduled windows on some hard-shell models. Check the display before assuming a hardware failure.
- Give it a full cycle before judging. At 1-3°F per hour, a tub genuinely needs many hours to climb from a cold fill or after a drain-and-refill — not being “hot yet” after an hour isn’t a fault.
- Rule out a leak. A tub that heats, then goes cold again, often has a slow leak dropping the water below the intake over hours — see our hot tub leak repair guide for the bucket test that confirms it.
- Suspect the element last. If the GFCI holds, the filter is clean, the setpoint is right, water level is full, and a full cycle still produces zero temperature climb, the heating element (hard-shell) or PTC pump-heater assembly (inflatable) has likely failed. See our hot tub heater replacement guide for the exact part your tub type needs.
Inflatable vs. hard-shell: what’s actually different
Intex and Coleman/SaluSpa inflatable tubs bundle the pump and heater into one sealed 120V assembly built around a self-limiting PTC (positive temperature coefficient) ceramic element — there’s no separate “just the heating element” part to replace, and no error-code display beyond a temperature readout that simply stops rising. Hard-shell 240V spas (AquaRest, Lifesmart, most dealer-installed cabinets) use a standardized titanium or Incoloy flo-thru element inside the equipment pack, often paired with a Balboa- or Gecko-style control board that’s more likely to surface an actual fault code for a flow or sensor problem. That structural difference is why the fix on an inflatable is almost always “replace the whole pump-heater unit,” while a hard-shell spa can often have just the element, the flow switch, or a hi-limit switch replaced individually.
Klein Tools GFCI Outlet Tester
- Plugs directly into the spa's GFCI outlet (or a standard outlet upstream of a hardwired disconnect) and lights up to confirm the circuit is live and properly grounded.
- Worth keeping on hand specifically because a GFCI can trip again within minutes of a reset if there's an underlying moisture or wiring issue — this catches that before you waste time chasing the wrong part.
- A five-minute check that rules out the single most common cause of "no heat" before you touch anything on the tub itself.
Ordering the wrong part after a misdiagnosis means a return shipping label and another week of cold water — start a free 30-day Amazon Prime trial so a same-day-confirmed GFCI tester or replacement element actually gets there before the weekend soak.
| Symptom | Likely cause | Fix | DIY or pro |
|---|---|---|---|
| No heat, no display, nothing running | Tripped GFCI | Reset the outlet/breaker | DIY |
| Pump runs, jets work, but water stays cold | Clogged filter tripping flow switch | Rinse or replace filter, restart cycle | DIY |
| Heats, then goes cold again over hours | Slow leak below the intake | Run the bucket test, seal or patch the leak | DIY (patch) / pro (major leak) |
| Only heats at certain times of day | Economy/sleep mode enabled | Check control panel settings | DIY |
| GFCI trips repeatedly, won't hold a reset | Electrical fault (element, wiring, moisture) | Diagnose the short before replacing anything | Pro |
| Everything checks out, still zero temperature climb after a full cycle | Failed heating element or PTC assembly | Replace the element (hard-shell) or pump-heater unit (inflatable) | DIY (inflatable) / pro (hard-shell element) |
When it’s actually a pro job
A GFCI that won’t hold a reset, or trips again within minutes, points to a real electrical fault — a shorting element, damaged wiring, or moisture inside a connection — and is worth a technician’s time rather than repeat resets. On a 240V hard-shell spa, anything past swapping the flo-thru element itself (control-board faults, wiring inside the equipment pack) is also best left to someone comfortable working at that voltage; see our hot tub wiring guide for what that circuit is supposed to look like in the first place. Inflatable tubs are more forgiving here since the whole pump-heater unit is a plug-and-play swap, not a wiring job.
The bottom line
Most “hot tub not heating” calls trace back to one of two boring, free-to-check causes — a tripped GFCI or a clogged filter choking the flow switch — not a failed heating element. Work the list in order: GFCI, water level, filter, setpoint/mode, a full heating cycle, then a leak check, before you assume the element is dead and spend money on a replacement part. Keep the routine tight going forward with our hot tub maintenance guide, and if you’re heating through genuinely cold weather, our best inflatable hot tub for winter guide covers which freeze-protection features actually matter.