Repairs
Hot tub not heating? What to check first
Safe checks you can do yourself when a hot tub won't heat, in the order that usually finds the problem fastest, and the parts that need a technician.
When a hot tub stops heating, the cause is often simple: a tripped GFCI or breaker, a temperature setting or economy mode, low water, a dirty filter or an airlock after refilling. Work through the checks below in order. If the tub still won't heat, or it keeps tripping the power, it's time for a technician.
Safety first
A hot tub combines water with 240 volts (120 volts on plug-and-play models), so a few rules come before any troubleshooting:
- Turn the power off at the breaker or the GFCI disconnect before you open the cabinet or touch any equipment.
- Don't open the control box. The checks in this guide only involve the panel, the water, the filter and the valves.
- A GFCI that trips is telling you something. Reset it once; if it trips again, leave it off and call for service. Common causes are moisture in a component, a failing heater element or a pump fault.
- In freezing weather, don't wait. A tub that isn't circulating can freeze and crack its plumbing.
Read the panel first
Most tubs show a code when something stops the heater. Codes vary between control systems, so check your owner's manual or the sticker inside the equipment door for the exact meaning. These are common examples:
| What you might see | What it usually points to |
|---|---|
| FLO, FL or similar | Not enough water flowing through the heater: dirty filter, low water, an airlock, a closed valve or a pump problem |
| OH, HH, HL or similar | Overheat or high-limit: the water or the heater got too hot, often because of poor flow |
| dr, dry or similar | The heater may be dry: low water or trapped air |
| A sensor code | A temperature or high-limit sensor isn't reading properly |
| ICE or a frost symbol | Freeze protection is running in cold weather (normal) |
With an overheat code, don't get in. Many manuals say to take the cover off, let the water cool, and clean the filter before the tub will run normally again.
Checks you can do, in order
1. Power and the GFCI
Is the topside panel lit? If not, check the tub's breaker and the GFCI disconnect near the tub. Reset once. If the pumps run but the water stays cold, move on to the next checks.
2. Temperature setting and modes
Check the set temperature first; it's easy to bump. Then look for economy, sleep or rest modes, which only heat during filter cycles. After a power outage some tubs lose their clock, so filter and heat cycles can end up running at odd hours.
On many plug-and-play tubs the heater switches off while the jets run on high, because a 120-volt circuit can't power both at once. That's normal: turn the jets down and the heater comes back on.
3. Water level
The water should cover the skimmer opening. Low water lets air into the pump and heater, which triggers flow or dry-heater codes. Top it up and give the tub a few minutes.
4. A dirty filter
This is the most common cause of flow problems. Turn the power off, take the filter out and look at it. If it's dark or clogged, clean or swap it. Some manuals allow running without the filter for a short test to see whether the heater comes back; if yours does, put a clean filter in straight after. Our maintenance guide explains how to clean filters properly.
5. An airlock after refilling
If you've just refilled the tub and a pump hums but moves little water, there's probably trapped air. With the power off, slowly loosen the large union nut on the pump's outlet until water starts to seep out, then tighten it again and turn the power back on. Running the jets on high in short bursts can also push the air through. Next time, fill through the filter well to avoid it.
6. Closed valves
Many tubs have gate or slice valves on each side of the pump and heater so they can be serviced. If someone has worked on the tub, make sure every valve is fully open.
7. Frozen or blocked lines in a cold snap
If the tub lost power during a freeze and won't circulate now, the lines may have ice in them. Don't keep running a pump against a blockage. Keep the cover on, and call us; ice can crack pipes, pump housings and the heater.
8. The cover and the weather
A tub with a waterlogged, torn or missing cover loses heat fast, and in wind and cold rain it may struggle to keep up. Heating is also slower than people expect: a full-size 240-volt tub typically gains a degree or two Celsius an hour, and a plug-and-play tub much less. After a refill with cold winter tap water, reaching 38 to 40°C (100 to 104°F) can take the better part of a day or longer.
Problems that need a technician
If you've worked through the checks and the tub still won't heat, the problem is likely one of these parts:
- Heater element. Elements burn out or short to ground, and a shorted element often trips the GFCI.
- Pressure or flow switch. It tells the control board water is moving, and the heater won't switch on without it.
- High-limit sensor. A safety cut-out that shuts the heater off if it gets too hot; it can fail or keep tripping.
- Temperature sensor. If it reads wrong, the board thinks the water is already hot.
- Circulation pump, or the main pump's low speed. If water isn't moving, the heater won't run. A humming or grinding pump is a clue; see pump repair.
- Control board relay or wiring. Burned contacts or a loose connection can cut power to the heater.
These involve testing live circuits and opening the control box, so leave them to a technician. Our heater repair page explains what a visit involves.
When to call us
Book a service visit if:
- The GFCI trips again after one reset.
- You smell burning or see scorch marks or melted plastic.
- There's water in the equipment bay.
- An error code comes back after you've cleaned the filter, topped up the water and checked the valves.
- The panel shows a sensor code.
- It's freezing outside and the tub has no heat or circulation. Treat this as urgent.
When you get in touch, send the make, model and serial number (on a label in the equipment bay), the error code, what you've already tried and a photo of the panel. It helps us bring the right parts the first time. See hot tub repair and service.