Hot Tub Air Lock: How to Clear It and Stop It Coming Back

Last updated: September 2026

So you’ve drained and cleaned your hot tub. You’ve scrubbed, you’ve flushed the pipes, and you’ve waited patiently for it to fill. You can’t wait to get back in. Then you press the jets button and… nothing. You can hear the pump running, but no water comes out of the jets. No water, no bubbles, just a hum.

A hot tub without working jets is basically a fancy bath, and that’s not what you signed up for. The most likely cause is an air lock: a pocket of air trapped in the pump or pipework that stops the water flowing. It’s a problem most owners hit at some point, and the good news is that you can nearly always fix it yourself in a few minutes.

In this guide I’ll show you how to tell it’s an air lock, how to clear it, and how to stop it happening next time you fill up.

What is a hot tub air lock?

A hot tub pump is a centrifugal pump. It’s brilliant at moving water, but it can’t move air. If a large pocket of air gets trapped inside the pump housing (the wet end) or in a high point of the pipework, the impeller just spins in air. You hear the motor running, but no water gets pushed round.

It usually happens when the tub has been drained and refilled. As the water comes up from the footwell, air gets trapped in the pump and pipes instead of being pushed out through the jets.

You want to sort it straight away. The water flowing through the pump is what keeps its shaft seal cool and lubricated, so a pump running dry can overheat and damage the seal. And with no flow, the heater has no water moving over it. A modern spa pack should protect the heater with its flow or pressure switch, but you don’t want to rely on that. Replacing a pump or a heater element isn’t cheap, so let’s avoid it.

How do I know it’s an air lock?

It’s quite easy to tell. You probably have an air lock if:

• You turn on the pump and nothing comes out of the jets.
• Only a couple of jets work, or they splutter and surge.
• The jets are running but there’s no power in them.
• Your topside shows a flow or pressure error, such as FLO, PS, a pressure switch message, “dry” or “no flow”. The exact code depends on the make of spa pack. See hot tub FLO error and, for ACC packs, PSOL and PSOH errors.

Before you go further, make sure the pump is actually spinning. If it hums but doesn’t run, or cuts out after a few seconds, it’s more likely a capacitor or a seized motor than an air lock. My guide to hot tub pump capacitors covers that.

And check the easy things. Is the water level at least halfway up the skimmer opening? Are all the valves fully open? A slice valve left closed after a filter change looks exactly like an air lock. Is the filter clean? A badly clogged filter can starve the pump.

What causes an air lock?

• Filling the tub through the footwell. This is by far the most common cause.
• Low water level. If the level drops below the skimmer, the pump sucks air in.
• An air leak on the suction side. A loose union, a missing O-ring or a cracked fitting between the tub and the pump lets air in while the pump runs. If the air lock keeps coming back, suspect this.
• A clogged filter or blocked suction. The pump can’t get enough water, pulls a vacuum and cavitates.
• Equipment above the water level. On DIY builds where the pump sits higher than the water, water drains back out of the pump when it stops. More on that below.

How to fix a hot tub air lock

Work through these in order. Most air locks clear at step 1 or 2.

1. Use priming mode

Most modern spa packs have a priming mode, which usually starts automatically when you power up. On Balboa systems you’ll see “Pr” on the display. Balboa’s fill guide for its TP7 series says priming mode lasts 4 minutes, and the heater is disabled during it so it can’t fire under low or no flow.

While it’s in priming mode:

1. Turn on each pump in turn. On a two-speed pump, use high speed.
2. Watch the jets. You want a steady stream of water with no big bursts of air.
3. Balboa’s guidance is not to let a pump run without priming for more than 2 minutes. If it hasn’t primed by then, turn it off, wait, and try again.

2. “Burp” the tub

If priming mode alone doesn’t do it, try burping it. Think of it like burping a baby. You’re coaxing the trapped air out in stages.

1. Open all the jets fully, and open any air controls.
2. Turn the jets on for 10–15 seconds, then off again. Wait a few seconds. You should see at least a few bubbles.
3. Now run them for 20–30 seconds, then off again. You should see more air come out.
4. Then 30–45 seconds, and off. With luck you’ll get a big burst of air bubbles out of the jets as the air lock breaks.
5. Keep running the jets until there are no more bubbles, just a steady flow of water.

On a two-speed pump, switching between low and high speed a few times can also shift the air.

Keep an eye on the bubbles. If nothing at all is coming out of the jets after a few rounds, or you’re getting the same amount of air each time, stop. The air lock needs releasing at the pump, and running the pump dry any longer risks damaging it.

3. Bleed the air out

If burping doesn’t clear it, you need to let the air out by hand. Turn the power off at the isolator first. Then open the equipment bay or control room and try these, in this order:

The filter housing

Air loves to collect in the filter housing. If your filter has a bleed screw (air release valve) on the lid, loosen it until the air hisses out and water appears, then tighten it again. If there’s no bleed screw, top the housing up with water from a hose before you put the lid back on.

The pump bleed screw

Some pumps have a small bleed screw on the front or top of the wet end. Loosen it with a screwdriver. You’ll hear air hiss out, then water will start to dribble. When there’s water with no air, tighten it back up. That’s the pump bled.

The union on the pump outlet

If there’s no bleed screw, use the union instead. The pump has two big threaded union nuts: one on the inlet (usually on the front, facing the tub) and one on the outlet (usually on top). The outlet is the high point, so that’s where the air sits.

1. With the power still off, make sure the valves either side of the pump are open.
2. Slowly loosen the union nut on the pump outlet, by hand or with a pair of large grips, until you hear air hissing out.
3. Once the hissing stops and water starts to seep out, tighten the union again. Hand-tight is enough. Don’t overtighten it, because it can crack. Hot Tub Outpost gives the same advice in its air lock guide.
4. Turn the power back on and try the jets.

Have a towel ready, as a little water will come out. That’s a good sign.

4. Be patient, and repeat

Sometimes there’s more air in the system than you think, especially on tubs with several pumps. If the first attempt doesn’t work, go round again: bleed, prime, burp. It might take a few rounds, but you will get it out.

5. Last resort: drain and refill properly

If nothing works, drain the tub and refill it the right way, through the filter housing (see below). It’s a pain, but it almost always solves it.

Air locks on DIY hot tubs

On most DIY in-ground tubs, the control room is lower than the water level, so gravity pushes water into the pump and it primes itself. Air locks on these builds are rare, and if you do get one, cracking the pump union will usually clear it in seconds.

The problems start when the equipment sits above the water level, for example in a raised control room or a shed up a slope. A standard hot tub pump is not self-priming. Every time it stops, the water can drain back and leave the pump full of air. If that’s your layout, you have two choices:

• A priming arrangement that keeps the pump flooded. See using a priming circuit above ground on a centrifugal hot tub pump.
• A self-priming pump. See what are the self-priming hot tub pump options?

Better still, design it out at the planning stage. Where your equipment sits makes a real difference, and I’ve covered it in hot tub control room position.

If an air lock keeps coming back on a DIY build, look for an air leak on the suction side: a union without its O-ring, a joint that wasn’t glued properly, or a crack. Air can get sucked in through a joint that doesn’t drip water. My hot tub leak guide covers finding them.

When to call in a professional

If none of the above works, it’s worth getting a technician out. Check your manual or the manufacturer’s website for authorised service agents. Air locks usually aren’t covered by warranty, so expect a call-out fee unless you have a service plan. That said, a call-out fee is a lot cheaper than a new pump or heater element burnt out by running them dry.

If the pump runs but still won’t move water after all this, it may be a worn impeller or a failing motor. See should I repair or replace my hot tub pump? and the ultimate guide to hot tub pumps.

How to prevent air locks

The single best thing you can do is fill the tub properly. Just sticking the hose in the footwell is not the way to do it.

1. Fill through the filter housing. Take the cartridge out (or leave it in, depending on your filter) and put the hose into the filter standpipe or housing. That way the water fills the pipes and pump from the equipment side first and pushes the air out through the jets as the level rises.
2. Fill to the correct level, about halfway up the skimmer opening.
3. Open the bleed screws on the filter and pump while you fill, then close them once water appears.
4. Check all the valves are open before you power up.
5. Power up and use priming mode straight away, running each pump in turn.

My guide on how to fill a hot tub with water the correct way goes through it step by step, and how to drain and clean your hot tub covers the other half of the job.

Parts and planning

If you need a replacement pump, union O-rings or a filter housing lid, you’ll find them at parts4tubs.co.uk in the UK and parts4tubs.com in the USA. If you’re planning a DIY build and want the equipment positioned so the pumps prime themselves, my hot tub plans and hot tub control room guide lay it all out.

FAQs

How long does it take to clear a hot tub air lock?

Usually a few minutes with priming mode and burping. If you need to bleed the pump, allow 15–30 minutes. A stubborn one on a tub with several pumps might take a few rounds.

Can an air lock damage my hot tub pump?

Yes, if you let the pump run dry for long. The water cools and lubricates the shaft seal. Balboa says not to run a pump without priming for more than 2 minutes, so turn it off between attempts.

Why does my hot tub keep getting air locks?

If it happens after every refill, change how you fill it: go through the filter housing. If it happens during normal use, the water level may be too low, or air is getting in through a loose union or leaking joint on the suction side of the pump.

Where is the bleed valve on a hot tub?

Most filter housings have a bleed screw on the lid, and some pumps have a small bleed screw on the wet end. If yours doesn’t, loosen the union nut on the pump outlet slightly instead, with the power off.

Will the heater work with an air lock?

It shouldn’t. With no flow, the pack’s flow or pressure switch should stop the heater and show an error. Balboa packs also disable the heater during priming mode. Don’t try to bypass these switches.

Still got dead jets after all this? Tell me what your tub is doing in the comments below. I read them all.

Cheers,
Andi

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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