Hot tub not heating
Quick answer
A tub that runs but will not heat is almost always a flow problem first: a dirty filter, low water, or an air lock starves the heater, so its safety cuts the heat. After that come a tripped high-limit, a bad temperature sensor, or a burned-out heating element. Check flow and the filter first, then the panel for an error code.
The heater needs a steady flow of water to fire, so most no-heat calls are really no-flow calls. Work down the list in order and you will catch the common, free fixes before paying for a part.
Check these in order
- Filter and water level. A clogged cartridge or low water cuts the flow the heater needs, so it shuts off to protect itself. Clean the filter and top up the water first. See cleaning the filter.
- Set temperature and mode. Make sure the set point is above the current water temperature and the tub is not in an economy, sleep, or summer mode that limits heating. It sounds obvious, and it is a common one.
- Clear an air lock. After a refill, trapped air stops the pump priming, which reads as no flow and no heat. The fixes are in jets not working.
- Look for a code, then reset. A flow or overheat code on the panel points to the cause; the error codes guide decodes the families. A flow trip or tripped high-limit often clears with a power cycle at the breaker once flow is restored.
- Sensor or element. If flow is good and it still will not heat, a failed temperature sensor or a burned-out heating element is likely, and both are a technician job.
A hot tub runs on mains power right next to water. Switch off at the breaker before opening the equipment bay, and leave heater element, sensor, or wiring repairs to a qualified spa technician or electrician.
If it will not turn on at all
A dark panel and dead tub is a power problem, not a heater fault. Check whether the GFCI breaker has tripped or a fuse has blown, and reset it once. If it trips again immediately, stop and treat it as an electrical fault to diagnose, not something to keep resetting. A tub that powers up but shows nothing on the topside can also be a panel or communication fault, which the error codes guide covers.
What helps
The cheapest and most common fix is a clean filter so the heater gets the flow it needs. A spare cartridge keeps the tub running while you soak the dirty one.
Get replacement spa filter cartridge Get filter cleaner
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Common questions
Why is my hot tub running but not heating?
Most often a flow problem: a dirty filter, low water, or an air lock starves the heater, which then shuts off the heat to protect itself. Clean the filter, top up the water, clear any air lock, and check for a flow code on the panel before suspecting the heater itself.
How do I reset the heater?
Once you have restored flow (clean filter, water topped up, air lock cleared), power the tub off at the breaker for a minute and back on. That clears a tripped flow or high-limit state. If it trips straight back out, the underlying flow or component fault is still there.
How long should a hot tub take to heat up?
Plug-in 110V tubs heat slowly, often around 1 to 2 degrees per hour, while wired 240V tubs heat faster. If yours is heating but just slow, that may be normal; the heat-up time calculator estimates it from your volume and heater size.