Troubleshooting

Why won't my spa heat up?

6 min read

A cold hot tub in January will get your attention fast. But before you brace for a big repair bill, take a breath — the large majority of "my spa won't heat" calls we run turn out to be something simple, and often something you can check yourself in a few minutes. A truly dead heater is actually one of the less common causes.

The key thing to understand is this: your spa can only heat water that's moving through it. The heater is a tube the water flows past, and if that flow is restricted for any reason, the spa senses it and shuts the heater off to protect itself. So "won't heat" is very often really a "won't flow" problem in disguise.

Things you can safely check yourself

1. Your water level

This is the first thing we check, because it's the most common. If the water has dropped below the skimmer, the pump starts pulling in air instead of water, and the heater cuts out. Top it off to the middle of the skimmer and see if it kicks back on.

2. The filter

A clogged filter is the single most common flow-killer we find. All the debris the filter has been catching eventually chokes it, flow drops, and the heater quits. Pull the filter, rinse it thoroughly, and run the tub for a bit without it as a test — if it starts heating with the filter out, you've found your culprit. Clean it well or replace it.

3. The settings

It happens more than you'd think: the temperature got bumped down, or the tub is in an economy or sleep mode that only heats during set hours. Check that the set temperature is actually above the current temperature and that you're in standard/ready mode.

4. The breaker

If the display is dim or dead, flip the breaker off and back on. A power blip — not unusual up here during a storm — can leave the system confused, and a reset clears it. If it trips again immediately, stop and call us; that's a signal, not a fluke.

5. An air lock after a refill

Just did a drain and refill? Air can get trapped in the pump, and trapped air means no flow. There's usually a simple bleed procedure for your model to release it. If the jets feel weak and it won't heat right after a refill, this is a likely reason.

Read the display Most spas tell you what's wrong. Codes like FLO (flow), OH (overheat), or a sensor warning point straight at the problem. If yours is showing a code, jot it down — it saves everyone time. We keep a plain-English guide to the common ones in our error codes article.

Things that need a technician

If the basics check out and it still won't warm up, the cause is usually one of these — and these are the ones to hand off:

A failed heater element. They don't last forever, and our hard water and constant winter run-time are hard on them.
A tripped high-limit or bad sensor. The safety that shuts the heater down can itself fail or read wrong.
A weak or failing circulation pump. If the pump can't move water properly, the heater can't do its job.
A flow or pressure switch. This little part tells the heater "flow is good, go ahead" — when it fails, the heater never gets the green light.

Why this one matters more in winter

Down at lower elevations, a spa that stops heating is an inconvenience. Up here, it's a clock. When it's well below freezing and the water isn't circulating and warming, you're now also risking frozen plumbing — which turns a modest repair into a much bigger one. That's why we treat no-heat calls in a Summit County cold snap as urgent, and why we'd always rather hear from you sooner than later.