Hot tub not heating
Usually, a hot tub not heating stems from a low set point, a tripped GFCI, or a dirty filter that blocks flow. Go through these checks in order, starting with quick fixes before examining the heater.
- Cut power to reset the high limit
- 30 seconds
- Top reason flow stops
- Dirty filter
- Flow-related codes that prevent heating
- E02 / FLO
- Heating an inflatable from cold
- 24 to 48 hours
Hot tub not heating: the checks in order
- Verify the power source. Inspect the GFCI on the power cord or subpanel, then check the house breaker. Reset a tripped unit one time. Hot Spring notes a GFCI that fails to reset may signal a ground fault.
- Verify the target temperature. The American Whirlpool manual states a power outage can revert the set point to default. Increase the setting and turn off economy or away mode.
- Look at the filter and water level. A clogged cartridge or low water will cut heater flow. Without flow, heating stops. Add water, then rinse the filter.
- Remove any airlock. Air trapped after refilling prevents the pump from circulating water. Find the procedure in the airlock section.
- Check the display screen. An error code identifies why heating stopped. Consult the code chart to resolve the issue.
- Perform a reset on the high limit. Shut off power for 30 seconds. Hot Spring notes this action resets a tripped high-limit thermostat, a device that usually trips due to low flow.
- Use a thermometer to test the thermostat. Per Hot Spring, temperature controls can be off by up to 5°F (2°C). If the gap is larger or the Ready light blinks, the sensor is likely the issue.
- Check the weather and close the cover. Cold, windy nights or an open lid can overwhelm a small heater. Hydropool states that over 90 percent of heat escapes from the surface of an uncovered tub.
- Look at the heater last. Intex puts a failed heating element among the causes, and that needs a service call.
Before opening any panel, turn off power at the disconnect or breaker. Do not open the control box on your own.
Error codes stopping the heat
When a tub is cold, most codes signal the heater detected no water flow. The heater stops itself so it can't get too hot.
| Code | Brand | What it means | What to do |
|---|---|---|---|
| E02 | Lay-Z-Spa | Water flow problem | Top up between the lines, then rinse the filter, take out stopper caps, and clear debris screens. |
| FLO | American Whirlpool | No flow at the heater | Reset the power, verify the heater pump runs, clean filters, and prime the pump |
| HL | American Whirlpool | High limit tripped | Stay out of the water. Top up with cold water, let the heater cool, then reset the power |
| OH | American Whirlpool | Water above 108°F (42°C) | Stay out. Remove the cover and top up with cold water |
| E90 | Intex | No water flow | Unplug the unit, clear the outlet grid, then clean or replace the cartridge |
| E94 | Intex | Water too cold | Unplug, add warm water until above 41°F (5°C), then restart |
| E99 | Intex | Temperature sensor broken | Call Intex service |
| Blinking power light | Hot Spring | High-limit thermostat tripped | Cut power for 30 seconds, inspect filters, and call if tripping continues |
| Blinking Ready light | Hot Spring | Temperature sensor problem | Turn power off for 30 seconds; call if blinking persists |
On its pump error codes page, Lay-Z-Spa provides one guide for each code from E01 to E18. It also looks for kinked liner pipes, worn washers, and cracked filter housings when dealing with E02.
Signs, probable causes, and solutions
| Symptom | Likely cause | Fix |
|---|---|---|
| Blank display, nothing runs | Power cut, tripped GFCI or breaker | Try one reset; phone an electrician if it trips once more |
| Display on, water cool | Set point low, or economy mode on | Raise the set point; switch to standard mode |
| Weak or surging jets, no heat | Low water or a clogged filter | Top up; rinse or replace the filter |
| No heat after a refill | Airlock in the pump or heater | Prime the pump |
| Heats, then the whole tub cuts out | High limit tripping on low flow | Clean the filter; call if it keeps tripping |
| Cools while the jets run | On 115 to 120 V tubs the heater pauses while the jets run | Normal; heat with the jets off |
| Heats very slowly | Open cover, cold wind, small heater | Close the cover and give it time |
| Every check passes, still cold | Failed element or sensor | Book a technician |
These rows match troubleshooting charts found in the Hot Spring manual, along with manuals from American Whirlpool and Intex. The heater shuts off while the jet pump runs on Hot Spring's 115 V models.
Clearing an airlock
Air can remain trapped in the pump after draining and refilling. The heater detects no flow while the jets surge or stay weak.
- To push air out, run the jet pump at high speed for sixty seconds, which Hot Spring does on a fresh fill. The tub is primed if jets are steady and strong.
- Does surging continue? Remove the filter cover. The American Whirlpool manual instructs you to turn on the water after pushing a garden hose into the filter hole. Then switch the pump from low speed to high and back.
- When Pr appears after power up, give it time. American Whirlpool says this is not an error but a 4 minute priming mode, requiring you to cycle the pumps on and off.
- The manual lists loosening a pump union with the pump running as a last resort. You'd have to take the side panel off for this, so a technician should do it.
Broken, or only slow?
Slow warming doesn't always mean something's wrong. Per Lay-Z-Spa, the heater raises water roughly 1 to 1.5°C, which is 2 to 3°F, every hour. Heating from cold can require 24 to 48 hours. While heating, its heater button glows red, turning green at the set temperature.
Certain heaters also pause by design. Heating stops on Hot Spring's 115 V models while the jets run. American Whirlpool tubs disable the heater if too many pumps run on high. Use the heat-up calculator to time your own tub.
The cover and cold weather
Heat escapes first through the open surface of the water. While the tub heats, keep the lid strapped and closed. Hydropool estimates 3 to 5 hours for refilling in mild weather if you use a good cover. Expect 6 to 8 hours or longer when the weather is cold.
Lay-Z-Spa starts its checklist with two questions. What is the outdoor temperature, and is the cover on or off? When air is below 39°F (4°C), Intex advises against using its spas; also, never run one with frozen water.
When you need a technician
You can reset a high limit or GFCI on your own. Hot Spring cautions that the same trip over and over could point to a deeper fault. Book a service visit when:
- The GFCI refuses to reset or trips again right away.
- The tub's breaker in the house panel trips. Hot Spring calls this a wiring fault or overload needing an electrician.
- Cleaning the filter and clearing the air does not stop the high limit from tripping repeatedly.
- Sensor codes like Intex E99 or a blinking Ready light remain active.
- You have good pump flow and the right set point, but the water stays cold.
Safety: cut power before opening panels
Your hot tub uses a high-power circuit located beside water. For any service, the American Whirlpool manual says to shut all power off first at the main breaker or the disconnect.
Hot Spring says no parts inside the control box are fixable by an owner, and opening it voids the warranty. Wiring needs a licensed electrician familiar with electrical requirements. Stay out of water until HL or OH codes disappear.
Common questions
Why is the hot tub not heating, even though the jets run?
A blocked filter or trapped air can halt heating while jets work, since the heater requires steady flow. On 115 to 120 V tubs, the heater also turns off when the jets run.
How can I reset my hot tub heater?
Leave the power off for a minimum of 30 seconds before switching it back on. This action resets a tripped high-limit thermostat, Hot Spring notes. If it trips a second time, clean the filter and check whether an airlock is present.
Can heating fail in a hot tub due to a dirty filter?
Yes. Flow through the heater drops when a cartridge clogs, triggering a flow sensor or high limit. Give the filter a rinse, or replace it when it's torn or still dirty after washing.
What does E02 indicate on a Lay-Z-Spa?
E02 indicates a fault in water flow. Lay-Z-Spa advises topping up water, rinsing the filter in lukewarm water, removing stopper caps, and clearing debris screens.
How long does a hot tub need to warm up?
A hard tub warms about 5 to 10°F an hour, Hydropool says. That's 3 to 6°C, so a fresh fill needs 3 to 8 hours. From a cold start, an inflatable Lay-Z-Spa may require 24 to 48 hours.