Hot Tub Leak? How to Find and Fix It (Pumps, Unions, Heaters and Pipes)

Last updated: September 2026

Finding a leak in your hot tub is one of the scariest feelings a hot tub owner can have. Your mind goes straight to costly repairs, technicians, call-out fees and more costs. Stop. Take a deep breath. Most hot tub leaks are easy to find and cheap to fix, and nine times out of ten they’re in the plumbing and equipment, not the shell.

I’ve had my share. When I first had my tub, I thought topping it up once a week was normal and it was just evaporation. It isn’t. You shouldn’t need to top up that often at all. If your water level keeps dropping, you’ve got a leak. I had a couple, and I’ll tell you about them below.

In this guide I’ll show you how to confirm it’s a leak, how to track it down, and how to fix the common ones: pumps, unions, heaters, filters, valves, jets, lights and pipework. There’s also a section for DIY in-ground tubs, where the rules are a little different.

Is it a leak or just evaporation?

Every hot tub loses some water. Warm water evaporates, especially with the cover off, and people splash out and carry water out with them. A year after fixing my leaks, I top up my tub every couple of months, and that’s down to evaporation and people getting in and out. It takes about 10 minutes with the hose to bring it back to the right level, which is the middle of the skimmer opening.

If you’re topping up every week, something’s wrong. To be sure, do a bucket test. It’s a trick borrowed from pool leak detection, and American Leak Detection explains the bucket test well:

1. Fill a bucket with tub water to near the top and stand it on a seat or step so it sits in the tub water.
2. Mark the water level inside the bucket and the level of the tub water outside it.
3. Leave it for 24 hours with the cover in its normal position and no one using the tub.
4. If the tub level has dropped more than the bucket level, you have a leak. If they’ve dropped about the same, it’s evaporation.

Run it once with the pumps off and once with them running normally. If you only lose water when the pumps are on, the leak is probably on the pressure (return) side of the plumbing.

How to find a hot tub leak

1. Start in the equipment bay

Turn the power off at the isolator first. Water and electrics in the same small space is not something to be casual about. Then open the equipment bay or control room and look for water, damp, white crusty deposits or rust. A torch is your best friend here. Check the pump, the heater, the filter, every union and every valve.

Remember that water travels. It runs along pipes and drips off the lowest point, so the drip you can see might be coming from a joint higher up. This catches people out more often than you’d think. Dry everything with a towel, then put some dry kitchen roll under each suspect joint and see which one gets wet first.

On a shop-bought spa with foam-filled cabinets, you may need to dig away soggy foam to find the source. Soggy foam is a good clue that you’re in the right area.

2. Let the water level drop

If you can’t see it, fill the tub to its normal level, turn the power off and leave it. The water level will drop until it reaches the leak, then stop. Look closely at everything just above the new waterline: jets, the skimmer, lights, pillows and fittings. If the water drops right to the bottom, the leak is low down, in the floor suction, main drain, a light or the pipework and equipment below the tub.

3. Use dye to pinpoint it

Once you’ve narrowed it down, turn the pumps off so the water is completely still, and squirt a little leak detection dye (or food colouring) right next to the suspect fitting. If there’s a leak, the dye gets drawn towards it. Swim University’s hot tub leak guide covers this method too.

Where hot tubs usually leak

Where	Signs	Usual fix
Pump or heater unions	Drips at the big threaded nuts	Hand-tighten; replace the O-ring or gasket
Pump shaft seal	Water between the wet end and motor; rust or water spots on the motor	Replace the seal, the wet end or the whole pump
Pump wet end	Leak around the pump body joint	Tighten the screws; replace the wet end seal
Heater	Drips at the unions, sensor or pressure switch; rust on the heater tube	Union gaskets or switch; replace a corroded heater
Filter housing	Drips at the lid, bleed screw or unions	Replace the lid O-ring or bleed screw seal
Valves	Weeping at the stem or body	Grease or replace O-rings; cut out and replace
Jets and lights	Water level stops at a jet or light	New gasket; epoxy putty on a cracked housing
Glued pipe joints	Steady drip at a fitting, often after frost	Cut out and remake; a patch or putty as a stopgap
Shell or structure	Rare; level stops at a crack line	Specialist repair (acrylic) or membrane repair (concrete)

How to fix a leaking hot tub pump

If you own a hot tub, chances are you’ll have a pump leak at some point. It’s one of those jobs that gets overlooked until you notice water pooling where it shouldn’t. The good news is that it’s usually straightforward. The leak nearly always comes from one of three places: the unions, the wet end, or the shaft seal. Power off at the isolator before you touch anything.

Step 1: Check the unions

The unions are the big hand-tightened nuts that connect the pump to the pipework. First make sure they’re tight. Sometimes a slight turn is all it takes. Hand-tight only, though. They’re plastic and they crack if you go at them with big grips. If they’re as tight as they’ll go and still drip, close the valves either side of the pump (if you have them), undo the union and check the black rubber O-ring inside. If it’s missing, flattened or damaged, that’s your culprit. Replace it, reassemble, and tighten by hand. Get the right size, as there are a few. See hot tub pump union sizes explained.

Step 2: Inspect the wet end

If the unions are dry, look at the wet end, the plastic housing where the water goes through the pump. First check that the screws or clamp holding it together are tight. Still leaking? Take it apart and check the seal between the two halves. If it’s worn or cracked, replace it, put everything back together and tighten evenly. There’s more in my ultimate guide to hot tub pump wet ends.

Step 3: Look for a failed shaft seal

Water dripping from the gap between the wet end and the motor, or rust and water spots on the motor casing, point to a failed shaft seal (sometimes called the mechanical seal). Don’t leave this one. The water runs along the shaft into the motor bearings, and once they go, the motor is done. Noisy, grinding bearings are often the first thing people notice. See noisy hot tub pump?

You can replace the seal, the whole wet end, or the complete pump. On an older pump, I’d usually replace the whole thing. A new pump comes with new seals, new bearings and a warranty, and you don’t end up paying for each part as the next one fails. My guide should I repair or replace my hot tub pump? helps you decide.

Heater leaks

Heaters leak from their unions, the temperature sensor, or the pressure or flow switch. Rust or white crusty deposits on the heater tube are a warning sign. Replacing union gaskets or a switch is a simple job. If the heater tube itself is corroded or pitted, replace the heater assembly, because those spots will leak later. Corrosion on heaters is very often down to low pH, so check your water balance too. There’s more in hot tub heaters explained.

A leak onto the spa pack or heater can also trip your RCD or GFCI. If that’s happening, don’t keep resetting it. Read my hot tub breaker tripping guide.

Filter leaks

This is probably the easiest place to find a leak. There are three places a filter housing leaks:

• The unions that connect it to the pipe. As with the pump, check they’re tight and that the rubber gasket is there and in good condition.
• The bleed screw (air release) on top. Check it’s tight and not weeping. It has its own small O-ring, which may need replacing.
• The housing lid. On a cartridge filter, the lid or body screws onto the base with a large O-ring. That O-ring gets worn and pinched as you take the lid off to clean the filter. Replace it, give it a light smear of silicone lubricant (not petroleum jelly), and you should be all set.

Valve leaks

Hot tubs use three main types of valve: shut-off valves (gate or slice valves), diverter valves and air control valves. The ones that carry water, the shut-off and diverter valves, are the ones that leak. Diverter valves usually leak because their O-rings have dried out or worn, so strip them down, replace the O-rings and grease them with silicone lubricant once a year. A leaking shut-off valve normally has to be cut out and a new one glued in.

Jet leaks

Think you’ve got a shell leak? A jet leak is much more likely. On acrylic spas, jet bodies seal against the shell with a gasket, and hot water breaks those gaskets down over time. The fix is to remove the jet body, clean the shell and the fitting, and fit a new gasket, usually with a bead of sealant as the manufacturer recommends. Jet manifolds can also crack if water freezes in them, which is a good reason to take winterising seriously.

Leaking lights

It sounds odd for a light to leak, but it’s usually the housing or recess it sits in, not the light itself. On older tubs with hot halogen bulbs, the lens can work loose or crack. A cracked lamp housing can often be fixed with plumbing epoxy putty from a hardware store. Get one rated to set underwater and you may not even need to drain the tub. Modern LED lights run far cooler, so if you’re replacing one, it’s worth upgrading. See the ultimate guide to hot tub lights.

Plumbing leaks: pipes and joints

Your hot tub plumbing is under pressure and handles hot water every time you use it. Over time, that stress can take a toll on joints and seals.

• If you can drain and dry it, the proper fix for a leaking glued joint is to cut it out and remake it with new fittings, primer and solvent cement.
• If you need a quick patch without draining, plumber’s epoxy putty that sets on wet pipes is your friend. Clip-on PVC repair clamps and two-part PVC repair kits are other stopgaps.
• If you can’t find it at all, a pour-in leak sealer can seal small, slow leaks in the plumbing. It won’t fix a pump shaft seal or a joint that’s failed properly. I’ve reviewed one in I’ve sprung a leak: “Fix a Leak” review.

Leaks in a DIY in-ground tub

On a DIY build, the equipment is usually in a separate control room and most of the pipework is buried, so leaks matter even more. Here’s what I learned the hard way.

My first leak: a T-joint

My first leak was a constant small drip from the bottom of a T-joint that linked the inlets and the skimmer before they went into the pump feed. I tried drying it and adding more pipe cement, but that wasn’t enough. What I ended up using was plumber’s wet putty, which is designed to stop leaks on wet or dry pipes and sets by chemical reaction even when it’s wet. I went through a couple of tubes to get it right, but it worked.

My second leak: the ozonator

The second was around the ozonator. It wasn’t working and I’d taken it out of service, but the pipework was still there, with too many weak joints. Anything held together with a jubilee clip in a pressurised system like a hot tub is going to leak, and that’s exactly what happened. With the jets on full, those joints were leaking at a rate of knots. I isolated the system, drained that section, cut it out and replaced it with regular pipe and two 90° elbows. Job done, no leaks. If you’re wondering whether you need ozone at all, read why you don’t need ozone in a hot tub.

My costly mistake: bent pipes

When I built my tub, I thought I’d reduce the risk of leaks by reducing the number of joints, bending pipes into place instead of using fittings. Fewer joints, fewer chances for water to escape, right? Wrong. By forcing pipes into awkward angles instead of making clean, square connections, I put stress on the joints I did have. Every one of those forced joints leaked at some point.

The dry joint that cost me a pump

Here’s my final confession. I once assembled part of my control room plumbing and forgot to cement a single 90° elbow. Everything seemed fine until one Sunday afternoon, watching the F1, I heard the blower speed up, and then everything went silent. The power had cut out. I rushed out to find the control room underwater and the tub drained by a third. That one dry joint had dumped water straight into my pump and fried it. An expensive mistake that a bit of cement would have avoided.

How to build it leak-free

If you want a leak-free tub, it comes down to one rule: a well-made joint doesn’t leak.

• Make clean, square joints. Cut square, deburr, dry fit, then use primer and solvent cement on every joint. The fittings designed for concrete hot tubs are incredibly reliable, as long as you glue them. See how to make the perfect PVC solvent weld joint.
• Use unions and valves around the pump, heater and filter so you can service them without cutting pipe.
• Don’t use hose and jubilee clips on anything under pump pressure.
• Pressure test before you bury or concrete over anything. Cap the lines, pressurise them, and leave them long enough to be sure nothing drops. Finding a leak now costs a fitting; finding it later costs a patio.
• Keep water away from electrics. Mount the spa pack above the plumbing, not below it, and give the control room a drain. See hot tub control room design considerations.

What about the structure? Out of all the tubs I’ve helped with, very few leak from the shell itself. When they do, it’s usually because the waterproofing membrane wasn’t applied properly or the shell wasn’t flood tested before tiling. If you suspect the structure, do the drop test with all the plumbing isolated or plugged. If the level still falls, it’s the shell. My waterproofing, grout and tile adhesive guide and in-ground hot tub build guide cover how to get it right first time.

Shell cracks on acrylic spas

It’s rare for an acrylic spa shell to leak. Most blisters and surface cracks are cosmetic. If you do find a crack that leaks, the usual approach is to drill a tiny stop hole at each end of the crack to stop it spreading, clean and dry the area thoroughly, and apply an acrylic and PVC repair kit. For anything bigger, get a specialist to look at it. There’s more on older tubs in restoring or repairing a hot tub or spa.

How to prevent leaks

• Every time you change the water, open the equipment bay and check for damp. Are the unions tight and dry?
• Look at the pump motor for rust or water spots. That’s the early warning of a shaft seal going.
• Keep your water balanced. Low pH and very high sanitiser levels eat seals, gaskets and heater tubes over time. The target ranges are in my hot tub chemical levels guide.
• Grease O-rings with silicone lubricant when you have things apart.
• Protect the plumbing from frost.

Planning your own build?

Most of the leaks I see on DIY builds start at the design stage: too many joints, no unions, pipes forced into place and no room to work in the control room. My DIY hot tub plans include the full plumbing layout and parts list, so you know exactly what goes where before you glue a single joint. If you’d like a second pair of eyes on your own design, I also offer a hot tub plumbing consultancy.

If you need replacement O-rings, unions, wet ends, pumps or heaters, you’ll find them at parts4tubs.co.uk in the UK and parts4tubs.com in the USA.

FAQs

How much water should a hot tub lose a week?

It depends on the weather, how often the cover is off and how much you use it, so there’s no single figure. As a guide, if you’re topping up every week, do a bucket test. If the tub loses more than the bucket, it’s a leak.

Why is my hot tub leaking from underneath?

Usually a pump union, the pump shaft seal, the heater or a valve. Water runs along pipes and drips from the lowest point, so dry everything and trace it back upwards. Power off first.

Why is my hot tub pump leaking?

Almost always a loose union or missing O-ring, the wet end seal, or a failed shaft seal. Rust on the motor means it’s the shaft seal, and that needs fixing quickly before water gets into the motor.

Do hot tub leak sealers work?

They can seal small, slow leaks in the plumbing that are hard to reach. They won’t fix a pump shaft seal, a loose union or a failed joint, so find the leak first if you can.

Can I fix a hot tub leak without draining it?

Often, yes. Unions and O-rings can be done with the valves closed, and plumbing epoxy putty that sets underwater can patch a small leak. Cutting out a glued joint or replacing a jet gasket usually means draining.

Should I keep using my hot tub if it’s leaking?

Not if it’s leaking near the electrics or the water level is falling below the skimmer. The pump can suck air and run dry, and water on the spa pack is dangerous. Turn it off at the isolator until it’s fixed.

Found a leak you can’t track down? Tell me about it 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