Avoid These 7 DIY Hot Tub Mistakes (I Made Them So You Don’t Have To)

Last updated: September 2026

When I built my own DIY hot tub, I made just about every mistake going. I’ve said more than once that this makes me more than qualified to help you with yours. Since then I’ve helped more than 1,500 people build their tubs with plans, parts and build consultancy, and I’ve seen the same mistakes come up again and again.

That’s why I started buildahottub.com and my YouTube channel: to help you build your own hot tub without repeating them. Here are the seven that cost me (and my customers) the most time, money and frustration, and how to avoid every one of them.

Mistake 1: Building it too big (and forgetting about heating)

The best DIY hot tubs aren’t the ones the size of a swimming pool. My first mistake was trying to build a tub that was far too big.

You can’t just make a hot tub as large as you like, because you have to heat it. More water takes more energy and more money to heat, and it takes longer to get up to temperature. That changes how you use it: you end up planning your soaks rather than jumping in when you feel like it.

I was always planning to heat mine electrically, and my first designs held around 3,000–3,200 litres (790–850 US gallons). The pool supplier suggested a 12kW heater for that volume, which is enormous. Luckily, “Pool Man John” reined me in. I scaled the design back to suit the 3kW heater I planned to use, which is the common size for electric heating in the UK and Europe. In the USA, 5.5kW is more typical.

Heating is also the decision that’s changed most since then. A few years ago, almost every tub I designed was heated by the spa pack’s electric heater. Today, almost every European build I design uses an air source heat pump, and in the USA, gas or propane is the most popular choice with my customers. Choose the method that suits how you’ll use the tub and your budget, and choose it before you finalise the size. See What is the best method to heat my DIY hot tub? and the ultimate guide to air source heat pumps for hot tubs.

How to avoid it: work out how many people you want in the tub and how much space each needs. That gives you the size you need, not the size you want. Then check you can heat that volume. There’s more in Key considerations for building a DIY hot tub.

Mistake 2: A control room that’s too small

If you’ve read my blog or watched my videos, you’ll know I go on about this a lot. For years, changing the filter on my tub was a pain, because the control room was too cramped to get at the pump, heater and filter. I’ve since rebuilt it. See My hot tub control room remodel.

Making joints in a confined space is hard. Servicing kit in a confined space is even harder. Plan the control room, lay the equipment out on the ground to check it fits, and leave room for your hands, your tools and a replacement pump. You’ll thank me the first time you change a filter. See Hot tub control room design considerations and where to put the control room.

The other space mistake is the cover. When you’re in the tub, where does the cover go? You don’t want to toss it on the lawn or the patio every time. Plan somewhere for it, or a lifter, before you lay the decking. See the ultimate guide to hot tub covers.

Mistake 3: Starting without a proper plan

“Fail to plan, plan to fail,” as the saying goes. The number of halfway-through rescue projects I’m asked to pick up each year is phenomenal.

I’ve picked up projects with pipes through the walls where the owner stopped because they had no idea what came next. I’ve picked up others where the wrong size pipe was used, and the owner couldn’t understand why there was next to no flow at the jets. Once the pipes are buried and the concrete is poured, fixing either is hard work.

How to avoid it: have a complete plan before you dig: dimensions, the plumbing layout with pipe sizes, the control room, the heating and the electrics. The more you plan, the more likely you are to build the tub you actually want. That’s exactly what my DIY hot tub plans give you. See also DIY hot tub plumbing: how to plan jets, pipe sizes, drains and the skimmer.

Mistake 4: Rushing the plumbing

Rome wasn’t built in a day, and neither is a DIY hot tub. It takes longer than you think. On average, I’d say 10–12 weeks is normal, depending on how much time and help you have (see How long does a DIY hot tub build take?). Where rushing really hurts is the plumbing.

If you make the joints properly, they won’t leak. It’s that simple. If you rush them, they will. Unfortunately, that’s exactly what happened on my build. It’s no secret that I’ve flooded my control room twice. The second time, I found a 90° elbow with no PVC cement on it at all. It was dry. I was clearly rushing that day, and it cost me a new pump.

A good solvent weld joint follows the same steps every time. Oatey’s solvent welding guide sets them out: cut the pipe square, deburr and chamfer it, dry fit, clean, prime, cement, then push the pipe fully into the fitting with a quarter turn and hold it for 30 seconds. The pipe must go all the way to the bottom of the socket. Then let it cure fully before you put any pressure on it. My step-by-step is in How to make the perfect PVC solvent weld joint.

Don’t avoid joints by bending the pipe

This one sounds odd, but I did it. I thought fewer joints meant fewer chances of a leak, so I tried to bend pipe around corners instead of using 90° elbows. In reality, the bent pipe didn’t sit properly in the fittings at each end, and those joints leaked. I had to cut them out and redo them. Use the elbows.

Don’t force pipe at the wrong angle

This is closely related. Fittings come in set angles, usually 90° and 45°. Stick to them and don’t force a pipe into a fitting at an angle it wasn’t made for. I brought the lower drains in with semi-flexible pipe (which isn’t as flexible as it sounds) and let it find its own way. Where the pipes met in the control room, they weren’t at the right angles, and I ended up with pipework all over the place. Keep runs parallel and square, and use proper 90° and 45° fittings.

How to avoid it: take your time on every joint, and pressure test the whole system before anything gets buried or concreted in. It’s much harder to fix a leak than to make a good joint in the first place. If you do end up with one, see How to detect and fix a hot tub leak.

Mistake 5: Plugging a pool light straight into the spa pack

This is still my favourite, only because it personally cost me about $1,000 in circuit boards. Those boards were around $300 each, and I was going through them fast. I did get some back under warranty (thanks again, Pool Man John).

Here’s what happened. The kids were already in, I’d just switched on the jets, the blower and the light. It worked for about five seconds, and then everything went dark. The fuse had blown and the spa pack was dead. I had no idea why, and I could have cried. It took a couple of engineer friends looking over the circuit diagrams to work it out.

The light output on a spa pack is a small, low-voltage AC supply meant for the pack’s own light, and it can only supply a limited current. For example, Balboa’s current BP packs rate it at 10V AC and 2A maximum, and older packs can be far lower. A typical 35W, 12V pool LED light draws around 3A. Plug one straight in and you overload that output. That’s what blew my boards.

How to avoid it: check the current draw of any light against the spa pack’s rating before you connect it. If you want a proper pool light, power it from its own supply. To solve this, I designed a spa pack connection kit, and it now comes with my Super Slim DIY hot tub and pool light, so you can switch it from the spa pack’s light button. There’s more in Can I control a swimming pool light with a hot tub spa pack?.

Mistake 6: Not reading the manual (electrics and set-up)

As someone not known for reading manuals, it pains me to say this, but you need to read the spa pack manual. Most “my hot tub won’t work” problems on new builds come down to one of these:

• The wrong supply. Especially in the USA, you need a 240V supply, not 120V, for the packs, heaters and pumps I use.
• The pack isn’t set for that voltage. Many packs can run on either, and you set it with a jumper on the board. Balboa’s BP system tech sheet, for example, shows one jumper position for 240V and another for 120V heater operation.
• Equipment in the wrong socket. I see this all the time: a pump plugged into the blower socket, for example. It’s one of the most common reasons something won’t turn on.
• The pack isn’t configured. It doesn’t know what you’ve connected. It’s very unlikely to leave the factory knowing you’re fitting, say, a circulation pump, a single-speed jet pump and a blower. If you don’t configure it, strange things happen: pumps and blowers don’t behave as they should.

The supply itself is a job for a qualified electrician: Part P in the UK, and NEC Article 680 with GFCI protection in the USA. See A guide to hot tub electrics and Configuring a Balboa spa pack.

Mistake 7: Jet bodies that aren’t square to the wall

The last mistake I made was not taking the time to set the gunite jet bodies flush and perpendicular to the wall. When I fitted the wall niche and eventually the jets, they sat at slight angles and didn’t fit flush.

It doesn’t actually stop the jets working. When the blower runs, a little air escapes from behind the jets, but once they’re full of water you won’t notice. It’s not the end of the world. But square, flush jets look far more professional and give you fewer problems later.

How to avoid it: keep each pipe perpendicular to the wall where it comes through, and fix the jet bodies so the face will finish flush with the tiles. See How to install gunite jet bodies in a DIY hot tub.

The mistakes at a glance

Mistake	What it costs you	The fix
Too big	Slow heating and high running costs	Size for people and heating together
Small control room	Awkward joints and miserable servicing	Lay the kit out first and go bigger
No plan	Wrong pipe sizes, weak jets, stalled builds	Full plans before you dig
Rushed plumbing	Leaks, floods and damaged pumps	Prime, cement, fully seat, use fittings and pressure test
Pool light on the spa pack	Blown circuit boards	Check the current and use a connection kit
Not reading the manual	Kit that won’t run or behaves strangely	Right voltage, right sockets, configure the pack
Crooked jet bodies	Jets that don’t sit flush	Set pipes square to the wall

For more of what I’d do differently, read What I’d change if I built my DIY hot tub again.

Want to skip the mistakes?

You might wonder why you’d take advice from someone who made all these mistakes. The truth is, we all learn from our mistakes, and I made plenty so you don’t have to. My DIY hot tub plans include CAD drawings with every dimension, the plumbing layout with pipe sizes, a full parts list and the video course, so you’re not working it out as you go like I was.

If you want something custom, I can turn your design into architectural CAD and a 3D plumbing design. If you’d like me checking the plumbing as you go, there’s plumbing consultancy for your build. And for parts that have been checked to work together, try parts4tubs.co.uk in the UK or parts4tubs.com in the USA.

FAQs

What’s the most common DIY hot tub mistake?

Starting without a complete plan. It leads to most of the others: wrong pipe sizes, a cramped control room, weak jets and tubs that are too big to heat affordably.

Why does my new hot tub plumbing leak?

Nearly always it’s a joint that wasn’t primed, cemented or pushed fully into the fitting, or pipe forced into a fitting at the wrong angle. Pressure test before you bury anything.

Can I plug an LED pool light into my spa pack?

Not directly. The spa pack’s light output is low-voltage AC with a small current limit, and most pool lights draw far more. Power the light from its own supply, or use a connection kit that lets the spa pack switch it.

Does a hot tub in the USA need 240V?

A built hot tub with a proper heater and jet pump needs a dedicated 240V GFCI-protected circuit, and the spa pack has to be set for 240V. Plug-in 120V tubs exist, but their heaters are much smaller.

How long does it take to build a DIY hot tub?

On average 10–12 weeks, depending on your time, help and the design. Don’t rush it, especially the plumbing.

Made a mistake I haven’t covered? Share it in the comments below and help the next person avoid it. 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