How to Restore or Repair an Old Hot Tub: A Step-by-Step Checklist

Last updated: September 2026

Restoring or repairing a hot tub is one of my favourite kinds of project. What I love most about what I do is the variety: custom new builds, “rescue missions” where things have gone wrong, and bringing tired old tubs back to life. Maybe you’ve bought a house with a neglected tub in the garden, picked up a “not working” spa for next to nothing, or inherited an in-ground tub with the control room ripped out. This post walks through the steps I’d follow to get it working again, in the right order.

Step 1: Check the structure

Whether you’ve got an old plastic shell tub or an abandoned in-ground tub in the backyard, start by looking at the structure.

Shell (portable) tubs

Take the cabinet panels off and have a good look inside. Older shell tubs often have a timber frame holding the shell in place. Full of water, a typical tub holds 1,000–2,000 litres (about 260–530 US gallons), which is one to two tonnes before anyone gets in. The frame has to carry that.

• Look for rot, soft timber, broken or split supports, and anything that’s been chewed. Replace anything suspect.
• Check the shell for cracks, blisters or delamination, especially around the footwell and seats. Small cracks in acrylic can often be repaired. Big structural cracks usually mean the end of the shell. Have a look at this fibreglass hot tub refurbishment case study for what’s possible.
• Check what it’s sitting on. A tub on soft ground or a crumbling slab will crack.

In-ground tubs

These are harder to check. If the tub sticks out of the ground at all, look at the walls for cracks or signs of movement. Give the inside a thorough clean and look for cracks that have opened up over time, and for loose or hollow-sounding tiles.

Epoxy resin or putty is fine for hairline cracks. For anything bigger, cut the crack out, fill it with a proper repair mortar, and put a pool-rated waterproofing membrane over the repair before re-tiling. My waterproofing, grout and tile adhesive guide covers the products. If a wall has moved, get a structural engineer to look at it.

Step 2: Check it holds water

Next, test the vessel on its own. Plug any pipes coming out of the tub, and block off the jets, drains and skimmer, so you’re only testing the shell or structure. Then fill it, mark the water level and leave it.

Leave it a full 24 hours, and stand a bucket of water next to it with its own level marked. If both drop by the same amount, that’s evaporation. If the tub drops more, you’ve got a leak. Nine times out of ten on the tubs I see, leaks are in the plumbing rather than the shell, but you want to rule the shell out first. For finding and fixing leaks, see How to detect and fix a hot tub leak.

Step 3: Check the plumbing

If a tub has been left unused, the pipework can go hard and brittle and crack, especially after a few winters with water left in it. Here’s what to look for:

• Crusty build-up (“gunk”) around joints. That usually means there is, or has been, a leak. Cut out and replace anything suspect.
• Union joints. Open every one and replace the rubber gasket or O-ring. If a union won’t open, cut it out and replace it. There’s no point keeping a union with a failed gasket, because it will just leak. Measure them before you order replacements, as pump unions come in different sizes.
• Split or perished flexible pipe, especially where it’s been rubbing or where rodents have been at it.
• Valves that are seized or weeping.

When you replace a section, use the right primer and solvent cement and do it properly. My guide to the perfect PVC solvent weld joint shows how.

Step 4: Work out which pipe does what

Quite often, as on one of the rescue projects I’ve worked on, the control kit has all been removed and the pipework just left hanging. You need to work out what goes where.

• Pipe size is a clue. The bigger pipes (typically 1.5in or 2in) are usually water. If there’s a mix of sizes, the smallest pipes are usually air lines to the blower.
• Find the suction first. Suction comes from the drains in the floor of the tub (and the skimmer, if there is one), and goes to the front of the pump. Returns go from the pump outlet to the jets.
• Use a hose. Start filling the tub with nothing plugged. The pipe that water comes out of first is the suction, because the drains are at the lowest point.
• Or push water through. Run a hose into a pipe. If it comes out of the jets, that’s a return. If it comes out of the drains, that’s suction.
• Count the pairs. Each pump that was originally fitted will have had a suction line and a return line. Look for the union nuts where the pumps used to connect, even if the pumps are long gone.

Label every pipe as you go. You’ll thank yourself later.

Step 5: Flush the pipework

With the pipes identified, give them a clean before you run anything under pressure. You don’t want to blast years of muck (and the odd dead animal) into the jets and block them all up.

1. Take out the jet inserts.
2. Put a pipe flush (line cleaner) into the pipework and move it round with a hose to shift the heavy debris.
3. Once the tub is working again, do it properly: add the pipe flush to the water, run the pumps for the time on the bottle, then drain, scrub the shell, rinse and refill. My guide on how to drain and clean a hot tub goes through it.

This matters for health, not just looks. The CDC says hot tubs have been linked to Legionnaires’ disease outbreaks, and that sediment and biofilm, temperature, water age and disinfectant residual are the key factors in Legionella growth. For commercial tubs brought back into service, it recommends scrubbing, replacing the filter and a heavy chlorine shock before refilling. A tub that has sat with stagnant water in it for years deserves the same treatment. Don’t get in until you’ve flushed it, cleaned it, fitted a new filter, shocked it and balanced the water.

Step 6: The control room

If a tub has been standing unused for a long time, or was sold as “not working”, the chances are there was a problem in the control room that never got fixed. If you’ve inherited parts, take them off and check each one on its own. You’ll want to replace all the O-rings and gaskets anyway.

A word on safety. Everything here is mains voltage near water. Only work on it with the power isolated at the breaker. I used to just put power to an old pump and blower to see if they ran, but I wouldn’t do that now. If you’re competent, you can bench test them with the correct voltage through an RCD or GFCI-protected supply. If you’re not, test them through the spa pack once it’s been wired by an electrician. An old supply needs checking too. It has to meet today’s rules: a dedicated circuit, RCD protection (UK) or GFCI (USA), and a local isolator. See Hot tub wiring explained.

The pump

• Does it spin? With the power off, turn the impeller by hand through the pump opening, and check the cooling fan on the back of the motor turns freely. If it won’t turn, it’s seized.
• Does it run? If it trips the breaker or RCD when powered, there’s water in the motor or the windings have failed. If it looks old, replace it. If it looks OK, dry it out and try again.
• Is it the wet end? Leaks from the pump itself are often the shaft seal, and the wet end can be replaced without a new motor. See Ultimate guide to hot tub pump wet ends.
• Hums but won’t start? It could be the capacitor, which is a cheap part to test and replace.

It is possible to repair seized pumps, but I’m in the “just replace it” camp for an old one. A new pump is a lot less hassle in the long run. I’ve weighed it up in Should I repair or replace my hot tub pump? Don’t run a pump dry for more than a second or two.

The blower

A blower is a simple piece of kit. Think of it as a hair dryer, usually without the heat. Heated blowers do exist, but they make no real difference to your water temperature. If it trips the power, water has probably got in. Blowers are inexpensive, so I’d replace rather than repair, and fit a new check valve at the same time so the new one stays dry. See Water in a hot tub air blower.

The spa pack

The spa pack is the brains of the operation. This video explains everything it does:

• Does the topside light up? When the pack is powered, you should see something on the control pad. If you get nothing, check the fuses. There are usually several on the board. The smaller ones typically protect the pack’s electronics, and the larger ones the pumps and heater.
• Find the wiring label. Most packs have a wiring diagram or label inside the lid. Even on old tubs they usually survive, as they’re out of the weather. It shows you where the fuses are and what rating they should be. Check them with a multimeter, as some breaks are too small to see.
• Check the heater. Heating elements are one of the most common failures. Look down the heater tube. If the element is rusted or scaled, replace it. See How to replace your spa pack heating element.
• Reset and reconfigure. Factory reset the pack and configure it from scratch for the pumps and blower you actually have. See Configuring a Balboa spa pack.
• Board or whole pack? If the board is dead, it’s often worth comparing the price of a board with a whole new pack. See Replace spa pack or just the circuit board?.

The filter

I wouldn’t bother trying to clean an old filter on a restoration. Measure it, look up the size and buy a new one. They’re cheap, and it’s not worth the hassle of an old filter breaking apart and clogging the system.

The cover

An old cover that’s been out in the weather is often waterlogged and heavy, which means it’s no longer insulating. Budget for a new one. See my guide to hot tub covers.

Step 7: Refill, balance and test

1. Refill through the filter housing to reduce air locks. If a pump won’t prime, see How to deal with a hot tub air lock.
2. Check every union and joint for drips with the pumps running.
3. Shock the water and balance it. Aim for the ranges in my hot tub chemical levels guide. The CDC recommends at least 3ppm free chlorine or 4–8ppm bromine, and a pH of 7.0–7.8 (CDC).
4. Let it heat up and watch for error codes. If it won’t heat, see Help! My hot tub is not heating. If it trips the RCD or GFCI, don’t keep resetting it. Find the cause first.

Common mistakes

• Powering up before checking the pump turns and the wiring is safe.
• Running the pumps before flushing, and blocking the jets with debris.
• Reusing old union gaskets and O-rings.
• Testing for leaks with the plumbing connected, so you can’t tell shell leaks from pipe leaks.
• Getting in before cleaning, shocking and balancing a tub that’s stood for years.
• Not reconfiguring the spa pack for the equipment actually fitted.

Need a new control room?

If the control room is missing or beyond saving, you’ll need to specify a pump, spa pack, blower and filter that suit the tub. My Ultimate Hot Tub Control Room Guide shows exactly how to put all of those parts together. For the parts themselves, head to parts4tubs.co.uk in the UK or parts4tubs.com in the USA. Before you buy, it’s worth reading control room design considerations.

FAQs

Is it worth restoring an old hot tub?

Often, yes, if the shell and frame are sound. Pumps, blowers, filters, heaters and even spa packs can all be replaced. A cracked shell or a rotten frame is usually where it stops being worth it.

How do I find a leak in an old hot tub?

Plug the pipework and fill the tub to test the shell on its own, with a bucket alongside to account for evaporation. Then check the plumbing, starting with union gaskets, pump seals and any joints with crusty build-up.

How do I tell the suction pipe from the return?

Suction comes from the floor drains (and skimmer) to the front of the pump. Fill the tub with nothing plugged, and the pipe water comes out of first is the suction.

Can I reuse the old filter?

I wouldn’t. A new filter is cheap, and an old one can break up and clog the system.

Is an old hot tub safe to use?

Only once the electrics have been checked by a qualified electrician, and the pipes flushed, the tub cleaned and the water shocked and balanced. A tub left standing can harbour bacteria, including Legionella.

Restoring a tub right now? Tell me what you’re working on 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