Troubleshooting guide
Hot tub not heating
Most spa controls refuse to heat when they can't prove enough water is flowing through the heater. That's a safety feature, and it means the fix is often a filter, not a heater.
Start with the easy, safe checks
- Is the spa getting power? If the topside is dark, check the GFCI (on the cord of plug-in models, or in the spa's subpanel) and the house breaker. Hot Spring's manual says that if a GFCI has tripped you reset it, and if it won't reset, that may mean a ground fault and needs a service tech. See GFCI keeps tripping.
- Read the topside. A message or code tells you why it isn't heating. Write it down exactly (or take a photo). Balboa and Gecko both publish what their codes mean: see Balboa codes and Gecko codes.
- Check the set temperature. Make sure it's set above the current water temperature and that the spa isn't in an economy, sleep or low-range mode.
- Water level and filter. Water should be above the skimmer opening. Pull the filter and run the spa briefly without it (power off while you remove it). If it heats without the filter, the filter is clogged and needs cleaning or replacing.
- Just refilled? Balboa systems run a priming mode after power-up, and the heater is disabled during priming. Hot Spring's manual also warns that very cold fill water can trip the high-limit. Give it time, and see airlock after a refill.
Flow codes are the most common reason
Balboa's flow-related checks are a good list for any brand: low water level, suction restrictions, closed valves, trapped air, too many closed jets and pump prime. Its HFL / LF messages mean there may not be enough flow through the heater to carry the heat away, so the heater waits or shuts off.
Gecko's FLO message means the system detected no water flow during the main pump's operation. Gecko's guide says to make sure the circulation valves are open, the water level is high enough, nothing is blocking the filter, no air is trapped in the plumbing, and the pump linked to the heater is running.
Spa runs, display shows dashes, nothing heats
On some Hot Spring models, dashes on the display mean the heater high-limit has tripped. The manual says to let the water cool and disconnect power for at least thirty seconds to reset it; if it keeps tripping, check for a clogged filter, then call for service. Other brands use different symbols, so check your manual.
What a tech checks next
On a video call, a tech will usually ask you to show the topside message, the filter and the equipment bay with the power off, plus the spa's model and serial label. From there they can tell if it's flow (filter, valve, airlock, pump), a pressure or flow switch, a sensor, the heater element or the control pack. Then you know which part to order, or whether you need someone on site.
Common questions
Why are my hot tub jets working but it won't heat?
Most controls only heat when they detect enough flow through the heater. A dirty filter, low water, closed valves or an airlock can stop heating while the jets still run. Check the topside for a flow message, clean the filter and top up the water first.
How long does a hot tub take to heat after refilling?
It depends on the spa, heater size, fill water temperature and weather, so check your owner's manual. Note that many controls start in a priming mode after power-up, and the heater doesn't run until priming ends.
Can I replace a hot tub heater myself?
Heater and control-pack work means opening high-voltage equipment. Leave wiring to a licensed electrician or a qualified spa technician, and always switch off the GFCI or breaker before opening the equipment bay.
Related guides
Balboa error codes
HFL, LF, dr, OHH, OHS, sensor and GFCI messages, from Balboa's own guides.
Read the guideGecko error codes
FLO, HL, OH, Prr, AOH and UPL, from Gecko's troubleshooting guide.
Read the guideGFCI keeps tripping
The spa shuts off and the GFCI won't stay on. Treat it as a safety signal.
Read the guideAirlock after a refill
Just drained and refilled, and now no jets or no heat? Prime the pumps.
Read the guideSources
- Balboa Water Group, Spa Touch 3 user guide: panel messages, flow-related checks and reminders
- Balboa Water Group, TP500S / TP600 system user guide (42339 rev A1): priming mode, freeze protection, GFCI trip test and message codes
- Gecko Alliance, Y-series and in.xe troubleshooting guide (9919-101313-D, rev. July 2023): FLO, HL, OH, Prr, AOH and UPL messages
- Hot Spring Spas (Watkins Wellness), Hot Spot collection SX/TX owner's manual: GFCI and high-limit checks, priming, drain & refill, winterizing and troubleshooting tables
Brand names belong to their owners. Hot Tub Helpline isn't affiliated with or endorsed by any manufacturer. Steps and codes vary by model and year, so always check your own owner's manual.