Hot Tub FLO Error: What It Means and How to Fix It

Last updated: September 2026

Have you just turned on your hot tub and seen “FLO” on the topside? If you’re here, that’s probably the case. Don’t panic. It’s one of the most common hot tub errors, and most of the time the fix is free and takes a few minutes.

In this guide I’ll explain what a FLO error actually means, why your tub stops heating, and how to track down the cause, starting with the easy checks and working up to the switch itself.

What is a FLO error?

A FLO (flow) error is your spa pack telling you it can’t sense water moving through the heater. Heating an element with no water flowing over it, or with air around it, would overheat it in seconds. So as a precaution, the pack shuts the heater off. Depending on the pack, the pump may keep running or it may be stopped too. Either way, the tub won’t heat until the flow problem is fixed.

Packs sense flow in different ways:

• A pressure switch on the heater, which closes when the pump pushes enough water through.
• A flow switch, which closes when water physically moves past it.
• Temperature sensors. Many newer packs compare two sensors on the heater instead of using a switch. Balboa’s current BP packs, for example, use sensors A and B, and modern Gecko packs use a flow sensor on the heater.

What FLO means on different packs

Not every brand uses the same code. Here’s what you’re likely to see, according to SpaDepot’s error code list and Gecko’s troubleshooting guide:

Pack	Code	What it means
Gecko (in.ye, in.yt, in.xe)	FLO	No water flow detected while the main pump runs. Gecko gives a minimum of 68 litres (18 US gallons) a minute
Gecko (pressure switch packs)	FLO / FLC	FLO: pressure switch open. FLC: pressure switch closed when it shouldn’t be
Balboa (pressure switch packs)	FLO	Improper flow or a pressure switch fault
Balboa (sensor-based packs)	HFL, LF, dr, dry	HFL: the heater sensors differ, which suggests low flow. LF: repeated low flow, heater shut down. dr/dry: not enough water in the heater
ACC	PSOL / PSOH	Pressure switch problems. See PSOL and PSOH errors
Hydro-Quip / Jacuzzi	FLO	Pressure switch alarm (Hydro-Quip) or flow switch, heater deactivated (Jacuzzi)

The causes, and the fixes, are almost always the same whatever the code. Check your own manual for the exact meaning on your pack.

Safety first

The first four checks below are safe for anyone. Once you’re opening the equipment bay or the spa pack, turn the power off at the isolator and breaker first, and make sure it can’t be switched back on. Anything inside the pack is for people who are competent with electrics. If that’s not you, stop and get a spa technician or qualified electrician in.

How to fix a FLO error, step by step

1. Check the water level

It sounds obvious, but make sure the tub is filled to the right level, usually around the middle of the skimmer opening. If the level is too low, the pump sucks air instead of water, the flow drops and the pack throws a FLO error.

2. Check the filter

This is one of the most common causes. A clogged filter restricts the water reaching the pump and heater. It’s very easy to test:

1. Turn the tub off.
2. Take the filter cartridge out.
3. Turn the tub back on and see whether the FLO error comes back.

If the tub now runs without an error, the filter is the problem. Clean it or replace it. How to clean a hot tub filter cartridge shows how. Don’t run the tub without a filter for longer than the test.

3. Check the valves

Make sure every gate valve and slice valve in the equipment bay is fully open. A valve left closed after a filter change or a drain looks exactly like a flow fault. On DIY builds, check any bypass valves too, including one around an air source heat pump.

4. Check for an air lock

If you’ve just refilled the tub or changed some plumbing and now have a FLO error, it’s very likely an air lock. Air trapped in the pump stops it moving water.

• Priming mode: most packs start in priming mode when you power up. On Balboa packs it lasts about 4 minutes with the heater disabled. Run each pump in turn and watch for a steady flow.
• Burp it: run the jets for short bursts, then longer ones, until the air comes out.
• Bleed it: with the power off, crack open the pump’s bleed screw or the union on the pump outlet until air hisses out and water appears, then retighten it by hand.

Don’t let a pump run dry for more than about two minutes. The full method is in Hot tub air lock: how to clear it, and How to fill a hot tub the correct way shows how to stop it happening next time.

5. Check the pump that feeds the heater

On many tubs this is the circulation pump. On others it’s jet pump 1 on low speed. If it isn’t running, there’s no flow, so there’s a FLO error. Check two things:

• Is it humming but not spinning? That’s usually a failed start capacitor or a seized motor. Replacing the capacitor often fixes it. See Hot tub pump capacitors.
• Is the pack set up correctly? If you’ve recently changed the spa pack, or added or moved a pump, the pack may be set for a pump that isn’t there, or the pump may be in the wrong socket. See How to configure a Balboa spa pack.

If the pump runs but the flow is weak, look for a blockage on the suction side or a pump that’s too small. Should I repair or replace my hot tub pump? can help.

6. Check the pressure or flow switch

This is less common, but switches do fail. If the pump is running and you can see water moving in the tub (in circulation mode, or on low speed), yet the FLO error stays, the switch or sensor is the likely cause.

• Scale and debris. Pressure switches have a small opening that can block with calcium. Good water balance helps prevent it.
• Adjustment. Some pressure switches have a small thumbwheel to adjust their sensitivity. Hot Tub Outpost explains how technicians set them with a meter. Others, such as the ones Arctic Spas uses, aren’t adjustable and are simply replaced.

The jumper test (pressure and flow switch packs only)

The quick way to test a two-wire pressure or flow switch is to bridge its two connections, which bypasses the switch. If the error clears, the switch is faulty. Arctic Spas describes the same test. But be careful, because you’re bypassing a safety device:

• Only do it if you can physically see the pump running and water flowing into the tub.
• Turn the power off before you fit or remove the jumper.
• It’s a diagnostic test for a minute or two while you watch it. Never leave a jumper in place, and never leave the tub heating with the switch bypassed.
• It doesn’t apply to packs that use temperature sensors or a flow sensor (such as current Balboa BP packs and Gecko in.ye, in.yt and in.xe). Their sensors aren’t a simple switch.

If the error clears with the jumper, replace the switch. If you’re not comfortable doing any of this inside a live control box, get a spa technician to do it.

7. Still getting FLO?

If the flow is good, the switch is fine and the error persists, the problem may be the heater sensor, its cable or the board. Gecko’s guide, for example, says to check the flow sensor cable on the heater, then replace the heater and finally the control. At this point it’s worth getting a technician in. If the tub is shop-bought and still under warranty, contact the retailer first, as opening the electrics yourself can void it.

FLO error quick reference

What you see	Most likely cause	What to do
FLO after a refill, jets dead or spluttering	Air lock	Priming mode, burp, bleed at the pump
FLO clears with the filter out	Clogged filter	Clean or replace the cartridge
Pump hums but doesn’t spin	Capacitor or seized motor	Test the capacitor; repair or replace the pump
FLO after a new pack or pump	Wrong setup or socket	Check the setup number and wiring
Good flow, FLO stays	Faulty or scaled switch	Jumper test (switch packs only); replace the switch
FLC (Gecko) with the pump off	Switch stuck closed	Replace the pressure switch

Preventing FLO errors

• Clean the filter regularly and replace it when it’s worn.
• Keep the water level up, especially in hot weather.
• Fill through the filter housing after a drain to avoid air locks.
• Keep the water balanced to reduce scale in the heater and switch.
• On a DIY build, make sure the pump that feeds the heater is big enough, and don’t leave a heat pump bypass too far open.

If the tub still won’t heat once the FLO error has gone, work through Hot tub not heating? For heater sizing and flow switches in more depth, see Hot tub heaters explained.

Parts

Filters, pressure switches, capacitors, heaters and pumps are available from parts4tubs.co.uk in the UK and parts4tubs.com in the USA.

FAQs

What does FLO mean on a hot tub?

It’s a flow error. The spa pack can’t detect enough water flowing through the heater, so it switches the heater off to protect it.

Can a dirty filter cause a FLO error?

Yes. It’s one of the most common causes. Take the filter out, restart the tub, and if the error clears, clean or replace the cartridge.

Why do I get a FLO error after refilling my hot tub?

Usually because of an air lock in the pump. Use priming mode, burp the jets or bleed the air at the pump. Filling through the filter housing next time helps prevent it.

Can I bypass the pressure switch on my hot tub?

Only briefly, as a diagnostic test, with the power off to fit the jumper and while you can see water flowing. Never leave it bypassed, because the switch is there to stop the heater burning out.

Will a hot tub heat with a FLO error?

No. The pack disables the heater until it detects enough flow again.

Still stuck with a FLO error? Drop your pack make and what you’ve tried in the comments below. I read them all.

Cheers,
Andi

You can also find me on my socials;

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi

 

Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi