Start with what your hot tub is telling you, because a spa narrows the problem down faster than a pool ever will. Is the topside flashing a FLO error? Did this start right after you drained and refilled? Is the pump humming but no water’s moving, dead silent, or just loud and gurgling? Each of those points somewhere specific, so find your symptom below and jump to it — this is the order I actually work a spa pad.
Most hot tub pump problems are flow problems, not dead pumps. A FLO error means the system sensed no water moving and shut down to protect the heater — usually a low water level, a dirty filter, a closed valve, or an airlock after a refill. Clear those first. A pump that hums without moving water points to a capacitor or a jam; a dead, silent pump points to power or the GFCI.
- A FLO (or FLC) error is the spa protecting its heater because it sensed no flow — fix the flow, don’t bypass the sensor.
- Right after a drain-and-refill, the cause is almost always an airlock — trapped air the circ pump can’t push past.
- Clear an airlock by loosening the top pump union until air hisses out and water flows, then retighten.
- Low water level, a dirty filter, or a closed gate valve will all throw a FLO error before the pump is ever at fault.
- A spa pump that hums but won’t spin usually needs a start capacitor; one that’s silent points to power or the GFCI.
FLO Error on the Topside Display
This is the big one, so let’s start here. A FLO (some brands show FLC) error means the spa’s flow sensor didn’t detect water moving while the pump was supposed to be running, so the computer shut the heater down to keep it from burning dry. It’s a safety feature, and I’ll tell you it’s almost never the pump itself. I work it in this order: check the water level first (it needs to cover all the jets and inlets — a low level lets the pump gulp air), then I pull and clean the filter, then open the cabinet and confirm every gate or slice valve is open. A spa filter is only good for about a year, so if cleaning doesn’t fix it, I replace the filter outright.
Don’t bypass the flow switch to make a FLO error go away. I know the trick — you can jumper the sensor — but that sensor is the only thing stopping the heater from cooking with no water across it. Jumpering it as a permanent “fix” is how people melt heaters and worse. Diagnose the flow problem; leave the safety alone.
It Started Right After a Drain and Refill
OK, so if the FLO error showed up the same day you drained and refilled, you’ve almost certainly got an airlock, and this is the single most common spa pump call I get. The pump can only move water — it can’t push a pocket of trapped air, so the air sits there blocking flow and the pump spins against nothing. The good news is it’s an easy fix once you know it.
I turn the heater off or all the way down first — if it kicks on while you’re purging, you’re gonna overheat it. Then I kill the breaker, open the cabinet, and find the pump. You’ll see two large union nuts where the plumbing meets the motor. I slowly loosen the higher one until air hisses out; in a few seconds water sputters, then runs steady. You gotta go slow or you’ll get a face full. Snug the union back down, restore power, and the flow comes back. Some newer spas have a dedicated bleeder valve that makes this even easier. If you’d rather not crack a union, the other method is to pulse the jets on high for ten or fifteen seconds at a time to burp the air through. It’s the same trapped-air principle I deal with on a pool that loses prime, just in a tighter package.
The Pump Hums but No Water Moves
So it’s getting power and you hear it humming, but nothing’s circulating. Two suspects. If it hums and the motor won’t actually spin, that’s a failing start capacitor nine times out of ten — the same cheap part and quick swap I cover in the capacitor guide. If the motor is clearly spinning but still no water moves, something’s blocking the impeller or it’s a worse airlock. I kill the power and check that the impeller turns freely. One honest warning: on a lot of spas the most stubborn blockage hides in the stainless heater manifold — leaves, biofilm, or a kid’s toy lodged in there — and those flow sensors are fragile enough that I usually hand a heater-manifold blockage to a tech rather than risk wrecking a sensor.
Is the Pump Completely Dead?
No hum, no lights, nothing? Then I stop chasing flow and go to power. I check the breaker and the GFCI test/reset button at the spa’s subpanel, since a tripped GFCI leaves the whole pump dead. I confirm voltage is actually reaching the pump before I condemn it — it’s the same dead-pump path I follow for any pump that won’t turn on. Circulation pumps in particular don’t fade out gradually; in my experience they either run or they don’t, so a truly dead circ pump that’s getting good power is usually a replacement.
It’s Running but Loud — Gurgling or Grinding
A healthy circ pump is nearly silent, so noise is a clue. Gurgling usually tells me there’s air still in the system — back to the airlock or a low water level. A dry screech or grinding growl is a different animal, and I treat it that way: that’s bearings, and on a spa pump it heads the same direction as any pump in my grinding noise guide. I had a customer swear their tub was “boiling” — it was just an airlock gurgling after a refill, cleared in two minutes at the union. I match the sound to the cause before spending anything.
The flow fixes — water level, filter, valves, airlock — are all free or a $15 filter. A start capacitor is $12 to $25. A replacement circulation pump runs $120 to $300 for the part, and a jet pump can run more. The places I’d call a pro: a blockage buried in the heater manifold (those sensors are easy to damage) and any persistent FLO error you can’t trace, since chasing it wrong risks the heater. Leslie’s has a solid hot tub circulation pump walkthrough that matches how I diagnose one.
How Do You Keep a Spa Pump Trouble-Free?
A spa pump lives an easier life than a pool pump if you stay ahead of a few things. I keep the water level up over the jets so it never gulps air, and I clean the filter monthly while replacing it about once a year — a clogged filter is behind a huge share of FLO errors. Every time you drain and refill, fill through the filter standpipe to push air out as you go, and be ready to burp a quick airlock at the union afterward. I keep the water chemistry balanced so scale and biofilm don’t build up in the plumbing and heater. And since the equipment lives in a damp sealed cabinet, glance at it now and then for leaks and tight unions. Do those and the pump quietly does its job, which on a good circ pump is most of its life.
Frequently Asked Questions
What does a FLO error on my hot tub mean?
It means the spa’s flow sensor didn’t detect enough water moving while the pump was running, so it shut the heater down to protect it. It’s almost always a flow problem — low water, a dirty filter, a closed valve, or an airlock — not a failed pump. Fix the flow and the error clears.
How do I get the air out of my hot tub pump?
Turn the heater off, kill the power, and slowly loosen the upper union nut at the pump until air hisses out and water starts to flow, then retighten it. Some spas have a bleeder valve instead, and you can also pulse the jets on high to burp the air through. I clear most airlocks at the union in under five minutes — it’s kinda satisfying once you’ve done a few.
Why did my hot tub pump stop after I refilled it?
That’s the classic airlock — draining and refilling traps air in the lines, and the pump can’t push past it. Bleed the air at the pump union or pulse the jets, and to avoid it next time, fill through the filter standpipe so the air gets pushed out as the tub fills.
My hot tub pump is humming but no water comes out — what’s wrong?
If it’s humming but the motor isn’t spinning, it’s usually a bad start capacitor, which is a cheap fix. If the motor is spinning but still no water moves, you’ve got a blockage or a stubborn airlock — kill the power, check that the impeller turns freely, and bleed the lines.
Do hot tub circulation pumps wear out slowly?
Not really — in my experience a circ pump either works or it doesn’t, rather than gradually pumping less. So if yours is getting good power and still won’t move water (and it’s not an airlock or a clog), it’s usually time to replace it rather than try to nurse it along.
Related Pool Pump Guides
- How Long to Run a Pool Pump — The Right Answer for Your Pool Size
- Pool Pump Cavitation — What It Is, Why It Happens, and How to Stop It
- Pool Pump Impeller Clogged — How to Diagnose and Clear It Yourself
- Pool Pump Strainer Basket Problems — Not Sealing, Cracked, and Clogged
- Pool Pump Weak Flow — What’s Blocking Your Suction and How to Fix It