Hot Tub Not Heating: The Checks, in Order

Last updated: October 2026

The most expensive mistake in spa troubleshooting is assuming "no heat" means "dead heater." Sometimes it does. But the heater element sits at the end of a chain of cheaper, commoner causes — and professional heater replacement runs $300–700, so it's worth the twenty minutes it takes to eliminate everything upstream of it. Work this list in order.

1. The mode — the $0 fault

Balboa's Economy mode heats only during filter cycles; Sleep mode barely heats at all. Gecko's economy modes behave the same way. A power outage, a curious guest, or a button pressed while cleaning can drop a spa into a mode that will never heat on demand — and the owner discovers it as a cold tub and a "broken heater."

Set Standard mode. Raise the set temperature above the current water temperature. Put the cover on. Then calibrate your expectations: a 240V spa gains roughly 1–2°F per hour (a 120V plug-and-play model less), so a genuinely cold spa is a tomorrow verdict, not a one-hour one. An uncovered spa in cold wind can lose heat as fast as the heater adds it.

2. Any code at all? Work the code, not the heater

A control that is protecting itself does not heat. Flow codes (FLO, HFL, Gecko's HL), sensor codes (SnA/SnB on Balboa, Prr on Gecko), and hardware codes (Gecko's Hr) all lock the heater out. If the display is saying anything besides a temperature, that message is the heating diagnosis — decode it first.

3. Flow — the heater's bodyguard

Heaters are flow-protected by design: weak circulation disables them outright, or lets them run in short bursts before the high limit cuts them off — which feels exactly like a dying heater. Run the filter-out test (breaker off, filter out, run the pump): if flow and heating return with the filter out, the filter was choking both. Check the water level, and if you refilled recently, bleed the air — our airlock guide covers it. Never authorize heater work on a spa whose flow you haven't verified.

4. The cold restart

Cut power at the breaker for a full 30–60 minutes. Latched high-limit faults and confused control states clear here on many packs. When you restore power, watch the display like a hawk and write down exactly what it shows and does — if this ends in a tech visit, that note is worth money.

5. Now the heater earns suspicion

Mode verified. No codes. Flow proven. Restart done. Still no heat? On a heat call — set temperature above the water, Standard mode — feel the outside of the heater tube, hands dry: it should warm noticeably. Stone cold on a heat call narrows the fault to three residents of the control pack: the heater element (failed open), a hi-limit sensor that has failed or latched, or the board's heater relay.

Inflatable spas: the same list, translated

On a Bestway/SaluSpa pump, "runs but won't heat" is usually one of four: a thermal cut-out that tripped and stayed tripped (watch for E06, or E08 — which needs the manual thermal reset most owners never find), a filter too dirty for the heater's flow protection, the cover left off in cold weather against a heater that only adds about 2–3°F per hour, or — last again — a failed element inside the pump unit, which is not user-serviceable. The E02 guide and the kit's inflatable playbook cover the reset procedure step by step.

The pattern across all of it: settings, protection, flow, restart — then hardware. Owners who work in that order mostly spend $0. Owners who start at the heater mostly spend $500 learning the order. Our free troubleshooter walks the same sequence with branching questions for your exact control system.