Hot tub not heating? Start with the simple things: the set temperature, the heat mode, a tripped GFCI or breaker, and the cover. If those check out, the usual cause is low water flow through the heater, which the control shuts off to protect itself. A failed element, sensor or high limit comes last, and that is technician work. This guide goes symptom by symptom and explains heater error codes from a Balboa control manual we opened.
Safety first: turn the power off at the breaker before you touch filters, panels or fittings. Only a licensed electrician should open the control box, test the heater element or work on wiring, and local code has the final word.
Hot tub not heating: symptom table
| Symptom | Likely cause | What you can check | Call a pro if |
|---|---|---|---|
| Water slowly cooling, no message | Low set point, Rest mode, filter times | Set temperature, heat mode, clock | Settings are right and it still will not heat |
| Panel dark | Tripped GFCI or breaker | Reset once | It trips again |
| Warm but never hot | Cover off or poorly seated, cold wind | Cover fit and condition | Rarely needed |
| HFL, LF or dr code | Low flow or air in the heater | Filter, water level, valves, jets, priming | Flow checks pass and the code returns |
| OHH or OHS code | Heater or water too hot | Flow checks, long pump runs | It repeats after flow is fixed |
| Sensor messages | Failed or mismatched sensor | Nothing beyond a power reset | Always |
The format mirrors our cold plunge chiller not cooling guide.
Quick checks before anything else
Set point and heat mode
Raise the set temperature a few degrees and watch for the heat icon. Then check the mode. The Balboa TP500 and TP500S user guide explains that Ready mode circulates water periodically to check temperature and heat as needed, while Rest mode only heats during programmed filter cycles. A tub left in Rest can feel cold most of the day with nothing broken. The Canadian Spa Company manual for the Toronto SE recommends Ready mode for winter.
Balboa also notes that a power loss can reset the clock, which moves your filter cycles (and Rest mode heating) to the wrong times. Reset the clock after any outage.
GFCI or breaker tripped
If the panel is dark, reset the GFCI or breaker once. If it trips again, stop. The Canadian Spa manual says most 240V GFCI tripping comes from incorrect wiring, which is a job for a licensed electrician.
Cover, cold weather and heat loss
The American Spas owner’s manual lists a poorly positioned cover as a cause of a spa that gets warm but not hot, and notes that covered spas use less electricity holding temperature. A cracked, waterlogged or loose cover lets heat escape faster than a small heater can replace it, especially on cold, windy nights.
Fresh fill and 120V tubs
After a cold refill, be patient: the Canadian Spa manual says a TOO COLD message may appear and the heater waits until the water reaches 45°F. On 120V tubs, the heater often pauses while jets run; our American Spas dual voltage listing states the heater and pump will not operate at the same time on a 110V installation. See 110V vs 240V hot tub.
Hot tub heater not working because of low flow
The heater needs water moving across it. Balboa’s flow related checks are low water level, suction restrictions, closed valves, trapped air, too many closed jets and pump prime.
- Dirty filter. The American Spas manual lists a dirty cartridge as a cause of weak jets. Our hot tub maintenance guide has the filter schedule.
- Low water. Below the skimmer, the pump draws air. Top up to the fill line.
- Closed valves and jets. The American Spas manual lists a closed gate valve as a cause of no heat and warns never to run the spa with gate valves closed. Open the jets and clear the suction fittings too.
- Air lock after a refill. Balboa systems enter Priming Mode at power up, with the heater disabled. If water is not flowing from the jets after 2 minutes, stop and repeat; if a pump will not prime, shut off power and call for service.
Some control systems confirm flow with a pressure or flow switch instead. If yours does and the checks above pass, testing that switch is technician work.
Hot tub error codes on Balboa panels
Many tubs use Balboa controls; the Canadian Spa Toronto SE listing names them. These meanings come from the Balboa TP500 and TP500S user guide for BP series systems. Other panels use different codes, so check your own manual.
| Code | What Balboa says | What to do |
|---|---|---|
| HFL | Heater flow may be reduced; retries in about 1 minute | Flow checks |
| LF | Not enough flow; heater disabled | Fix flow, press any button to reset |
| dr | Heater may be dry; spa shut down 15 minutes | Check water level and prime |
| OHH | Heater sensor read 118°F; spa shut down | Reset below 108°F, then flow checks |
| OHS | Water reached 110°F | Auto resets below 108°F; check long pump runs |
| Sensor A or B, sensor balance | Sensor failed or sensors disagree | Call for service |
Heater element and high limit: when to call a technician
If settings, power and flow are all fine and the tub still will not heat, the likely culprit is inside the equipment: the element, a sensor, the high limit or the board. The American Spas troubleshooting table says to contact your dealer for a defective heater. Call a technician when an overheat code returns after flow is fixed, any sensor message appears, the GFCI trips after a reset, or you smell burning near the equipment bay. Do not open the control box or meter the element yourself.
What we carry, and what we do not
We do not sell hot tub chemicals, filters, heaters or spare parts; get those from your tub’s manufacturer or dealer. What we carry helps with heat loss:
- Rolling Spa Cover for 84 inch spas: heat insulating XPE with a dome that sheds snow, per the listing.
- Top Mount Cover Lifter: makes replacing the cover easy; fits spas up to 96 inches.
- 8 ft Hot Tub Cover Weather Guard: protects your cover from ice and UV, though its listing says it is not insulating.
If you are replacing a tub, heater size and voltage matter most in cold climates:
| Tub | Power | Heater |
|---|---|---|
| American Spas Dual Voltage 18-Jet | 110V or 240V | 1.5 kW at 120V, 5.5 kW at 240V |
| American Spas 6-Person 40-Jet Lounger | 240V | 5.5 kW |
| Canadian Spa Richmond Plug and Play | 120V, 15A | 1.5 kW |
| Canadian Spa Toronto SE | 240V, 50A | 5.5 kW |
All four listings describe insulation layers. Browse our American Spas brand page, and see how much a hot tub costs.
Frequently asked questions
Why is my hot tub not heating but the jets work?
Check the heat mode; Balboa Rest mode only heats during filter cycles. On 120V tubs the heater may wait while jets run. Otherwise, look for a flow code.
Why is my hot tub heater not working after a refill?
Usually an air lock or very cold water. Balboa disables the heater during Priming Mode, and the Canadian Spa manual says heating waits until the water reaches 45°F.
What do hot tub error codes like LF and OHH mean?
On Balboa BP series panels, LF means not enough flow through the heater and OHH means the heater got too hot. Both point to flow checks first.
How hot should a hot tub get?
The Canadian Spa Company manual says spa water should never exceed 104°F, in line with CPSC guidance. If you have a health condition or are pregnant, ask your doctor first.
Need help with your hot tub?
Call us at 866-777-2590, Monday to Friday, 9AM to 6PM PST, for help matching a cover or choosing a tub. Orders of $999 or more ship free by freight; below that, shipping is a $200 flat rate. See our return and refund policy before you buy.
