How to Replace a Hot Tub Heating Element or Heater Tube (Balboa Spa Pack)

Last updated: September 2026

Hot tub gone cold? Before you order a whole new spa pack, it’s often just the heater. On a Balboa pack, the heater is a stainless tube bolted along the bottom of the pack with an element inside it. You can replace the element on its own if the tube is in good shape, or swap the whole heater tube if it isn’t. Both are jobs a careful DIYer can do in under an hour.

In this guide I’ll cover how to tell if the heater really is the problem, how to test the element, and then both jobs step by step, using a Balboa pack with an M7 heater along the bottom.

Is it really the heating element?

A tub that won’t heat isn’t always a dead element. Work through the easy things first:

• Flow. Is the filter clean, are the valves open, and is there an air lock? Balboa packs won’t heat without enough flow through the heater. See How to clean a hot tub filter and How to deal with a hot tub air lock.
• Settings. Is it in Rest or Economy mode, outside a heating window? See Balboa heat modes explained.
• Load limits. On a smaller supply, the pack turns the heater off while the jets run. That’s normal.
• Error codes. These point you in the right direction.

Balboa code	What it means	Usually
HL, HFL, LF	Big difference between the two heater sensors	A flow problem, not the element
dr, dry	Not enough water in the heater	Low water, an air lock or a blocked filter
OH, OHH, OHS	Overheat	Poor flow, or a hot day with long filter cycles
SnA, SnB, SnS	A sensor isn’t working, or the sensors disagree	A faulty sensor or a loose plug
No code, water stays cold, pump runs fine	Pack is calling for heat but nothing happens	A good time to test the element

Code meanings from SpaDepot’s Balboa error code guide. My full checklist is in Help! My hot tub is not heating. If your RCD or GFCI trips as soon as the heater comes on, a failed element is a prime suspect. See why your hot tub trips the breaker.

How to test a heating element

You need a multimeter. Isolate the power first at the local isolator and the breaker, and make sure it can’t be switched back on while you work.

1. Disconnect the two power connections from the element terminals.
2. Resistance test. Measure across the two terminals. A healthy element reads close to the figure in the table below. An open circuit (no reading) means the element has burnt out.
3. Earth test. Measure from each terminal to the metal heater body. You should get no reading at all. Any reading means the element has broken down to earth, which is exactly what trips an RCD or GFCI.

The expected resistance comes from the element’s rating: resistance = volts² ÷ watts.

Element	Where you’ll find it	Approximate resistance
2kW at 230V	Smaller UK/EU packs	~26 ohms
3kW at 230V	Most UK/EU Balboa BP packs	~18 ohms
4kW at 240V	Some US packs	~14 ohms
5.5kW at 240V	Most US DIY packs	~10.5 ohms

Readings within a few ohms of these are fine. SpaDepot’s element testing guide gives roughly 9–16 ohms for typical US elements, which matches. If the element tests fine, look at the sensors, the flow or pressure switch, and the board. Replace the spa pack or just the circuit board? helps with the next step.

Element only, or the whole heater tube?

Replace just the element if…	Replace the whole heater tube if…
The tube is clean, dry and not corroded	The tube is corroded, pitted or weeping
The sensors test fine and no sensor codes are showing	The sensors are faulty as well (some assemblies come with new ones)
You want the cheapest fix	You want everything new in one go, or the unions and seals are tired

Check exactly what’s included before you order. For example, the Balboa M7 heater assembly listed for US packs (5.5kW at 240V) comes as the 15in tube with its two sensors, split nuts and gaskets, with the element sold separately. Match the kW and voltage to your pack’s label.

Before you start: power and water

• Isolate the power at the isolator and the breaker. The heater terminals carry mains voltage.
• Stop the water. The heater tube sits in the plumbing and is full of water. Close the valves either side of the pack if you have them. If you don’t, drain the tub to below the level of the pack. See How to drain and clean a hot tub.
• Have towels ready. There’s always some water left in the tube.
• Take a photo of the connections before you disconnect anything.
• Use new gaskets or O-rings when you refit. Old ones rarely reseal.

Option 1: replace just the heating element

Removing the old element

1. Disconnect the power cables. Unscrew the top of the power unit, then carefully disconnect the two power connectors from the element.
2. Remove the temperature sensor. Use a spanner to loosen it and take it out of its housing.
3. Pull the element out. Reach in from the side and slide it out of the tube. Look inside the tube while it’s open. Heavy scale or corrosion is a sign the tube should be replaced too.

Fitting the new element

1. Insert the new element. Line it up with the mounting holes. This can be a bit fiddly, so take your time. Prop it up slightly and secure it with the washers and bolts. Don’t overtighten.
2. Refit the temperature sensor. Drop the probe back into its housing and tighten the nut to secure it.
3. Reconnect the power cables. Put them back in their positions and bolt them down firmly. Loose terminals run hot.

Option 2: replace the whole heater tube

This works on the Balboa pack in the video. Many other packs use the same idea with different fixings.

Removing the heater tube

1. Unplug the two temperature probes. There’s a small release button on the right of the panel. Reach in and press it to free each probe.
2. Unplug the power unit. It’s a simple plug-in (Molex-type) connection.
3. Undo the plumbing connections if your heater is joined to the pipework with unions or split nuts.
4. Remove the two bolts holding the tube, one at the bottom and one at the top right of centre, with a small spanner.
5. Slide the heater tube out of the pack, catching the water that’s left inside.

Fitting the new tube

1. Put the new heater tube in place and line it up with the bolt holes.
2. Refit both bolts.
3. Reconnect the power plug to the heater.
4. Plug both temperature probes back in.
5. Remake any unions or split nuts with new gaskets, hand tight plus a little. Don’t use sealant on union gaskets.

Refill, purge and power up

This is where new elements die, so don’t rush it.

1. Open the valves or refill the tub, and check both unions for drips before the power goes back on.
2. Get the air out. Crack open a pump union or bleed valve until water runs, then tighten it. An element with an air bubble around it can burn out almost instantly. See How to fill a hot tub the correct way.
3. Power up, run the pump, and check the pack calls for heat and the temperature starts rising.
4. Check again after an hour for leaks and for any RCD or GFCI trips.

Why elements fail (and how to make the new one last)

• Dry firing. Low water, an air lock or a clogged filter leaves the element without water around it. Keep the filter clean and the water level up.
• Scale. Hard water coats the element, which then overheats. Keep calcium hardness in range. My hot tub chemical levels guide covers it.
• Corrosion. Low pH and very soft water eat away at elements and heater tubes. Keep pH at 7.2–7.6.
• Age. Elements are a consumable, and after a few years they simply wear out.

There’s more on heater types and sizing in Hot tub heaters explained. If you’re fed up with electric heating costs, air source heat pumps for hot tubs are worth a look.

Parts

Replacement elements, heater tubes and sensors for Balboa and other packs are available from parts4tubs.co.uk in the UK and parts4tubs.com in the USA. Have your pack model and the heater’s kW and voltage to hand when you order. If the pack itself is past saving, see How to select a replacement spa pack.

FAQs

How do I know if my hot tub heating element is bad?

If the pump runs, the flow is good and the pack calls for heat but the water stays cold, test the element. With the power isolated, an open circuit across the terminals, or any reading from a terminal to the heater body, means it has failed.

What resistance should a hot tub heater element have?

Resistance = volts² ÷ watts. That’s about 18 ohms for a 3kW element at 230V, and about 10.5 ohms for a 5.5kW element at 240V.

Can I replace just the element instead of the whole heater?

Yes, if the tube, sensors and seals are in good condition. If the tube is corroded or leaking, replace the whole heater assembly.

Do I need to drain the hot tub to replace the heater?

Not if you have valves either side of the pack. Close them and you’ll only lose the water in the tube. Without valves, drain the tub below the level of the pack.

Why does my new element keep failing?

Usually dry firing from an air lock, low flow or low water, or scale from hard water. Fix the cause, or the next one will go too.

Stuck with a heater that won’t play ball? Drop your pack model and the symptoms 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.

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