Spa Parts Terminology

Glossary of Spa and Hot Tub Parts Terms! 

hot tub cutaway showing internal hot tub spa parts

We talk to customers all day long about their spas and hot tubs, we train on the language of spas and hot tubs, and the terms to describe the hundreds of individual parts used to build them.

Today's post is the terminology of spa and hot tub parts, to help you better identify and discuss, all of the various components on your spa and hot tub equipment. Want to add a term to our spa parts glossary? Leave me a comment below with your whatcha-ma-callit!

Air Buttons:

Air Buttons are used spa-side on an air-control systems or pneumatic controls, to activate equipment such as pumps, lights, blower. Pushing the Air Button will send a pulse of pressurized air through an air hose, to activate an Air Switch.

Air Injectors:

Air Injectors are found on the floor or seats of spas and hot tubs to distribute air from a air blower motor. Air Injectors have a PVC connection on the inlet side and a diffuser cap with many holes on the outlet side.

Air Manifolds:

Air Manifolds are some of the wildest looking spa parts we sell! A Manifold is used to split the flow of air from one large pipe into many smaller hose barbs. Air Manifolds are typically 2" or 1.5" inlet and 3/8" hose barb outlet.

Air Switch:

Air Switches are used with air buttons, to activate spa and hot tub equipment, when using an air-control system, aka older style pneumatic controls. Air Switches can be a simple on/off switch for a blower or light, or more complex switch that will sequentially control many functions.


bromine feeder or dispenser for constantly and consistently adding small amounts of bromine sanitizer to a spa or hot tub. There are bromine floaters, or a free-standing Brominator can be plumbed inline on the spa return line or off-line where space is an issue.


Start Capacitors are s small battery that helps spa pump motors get up to speed quickly (3450 RPM), Run Capacitors alternate current to one or more windings of a single phase AC induction motor to help create a rotating magnetic field to reduce motor workload. 

Check Valve:

Check Valve is a one-way flow valve, and is used for both air, water and ozone systems in spas and hot tubs. Spa blowers always have a check valve on the plumbing to allow air out, but not allow water in. Ozone check valves keep water out of the ozone hose and ozonator.

Chip Number:

On a PCB or printed circuit board, there is a Chip Number printed on the main chip, often referencing a Revision Number. When replacing a spa circuit board on a spa control, be sure to match chip number and revision, and superseded versions.


A Contactor is a large relay or an electric switch rated for high amperage. Contactors are used on larger electric heaters such as C-SPA or Coates heaters. Fairly sturdy items, but subject to damage under excessive loads or chattering.


Your Spa Control is the brain of the hot tub. Spa Controls are digital and fully electronically controlled. Older spa controls are pneumatic systems with Air Controls. New Spa Controls are typically sold with a new heater and new topside control panel.


Pump Diffuser is used to evenly diffuse water flow, inside of a pump, a filter or returning to the spa. Ozone diffusers are also used to provide for even ozone disbursement.


Diverter is used inside of a valve, to divert water flow into or from one or more pipes. Large spas often have spa side knobs that can be turned to activate different banks of spa jets. The knob, connected to a shaft, is turning a diverter inside of the valve.


Hot tub Heater Elements are similar to those found in electric hot water heaters, or the coiled burners found on electric cook tops. Spa heater elements can be replaced when they develop problems, but those with the Balboa style tube heater just replace the entire heater assembly.


An Escutcheon Plate is a trim ring used around spa jets, aka spa jet wall fitting or spa jet escutcheons. Spa side buttons often have a shiny retainer ring escutcheon used as trim, and Escutcheon plates are also found around spa grab rails used on inground spas.


Spa Filter can refer to both the entire filter assembly, or can be used to refer to the internal spa filter cartridge. Spa Filters are rated for 12-24 months for most residential use. Keep an extra spa filter on hand, so you can dry them completely after cleaning; kills more bacteria.

Flow Switch:

Electric spa heaters can basically melt-down if the water flow isn't proper, a Flow Switch is a electro-mechanical device that plumbs in front of, or sometimes after, the spa heater to monitor flow rate. Harwil type paddle switches are common, but there are many others.

Heat Manifold:

Spa Heater Manifold is a plastic or steel box or tube used to house an electric spa element. They have connections for incoming and outgoing water, sensors and the element terminals.

High Limit Switch:

Another spa heater part, High Limit Switches are used to sense the highest limit of temperature. Typically two high limits are used, to measure incoming and outgoing water temperature. OH and HL error codes are produced when they sense an overheating situation.


The Spa Pump Impeller is similar but opposite in design to a boat propeller. Impellers are designed to draw water in and push it out forcefully. Most spa pump impellers are closed vanes, and they can become clogged with seeds or debris of a certain size.


Water coming into a spa or hot tub, such as through a spa jet or foot jet, is known as an inlet. There are hundreds of styles of spa inlets, by Balboa, G&G, HydroAir, Jacuzzi and Waterway.


Spa Jet Parts is quite a large term encompassing many other parts. The Spa Jet Body is the main housing of a spa jet, which holds the Jet Internal and Nozzle, held in place by a Jet Retainer or Wall Fitting.

Lock Nut:

Lock Nuts are used around spas and hot tubs in many places, to secure a filter cover or wall fitting tightly to the spa shell. Also used on spa unions, and behind each jet, Lock Nuts, aka Lock Rings are ubiquitous parts on spa and hot tub equipment. See also: Split-Nut Union.


Hot Tub Motors are used on spa jet pumps and spa circulation pumps, to turn the Impeller, which drives the filtering and sanitation equipment. Forced air spa blowers also have motors, and ozonators likewise have tiny air pump motors and time clocks have a small timer motor.


Some Spa Jets have a Nozzle, or an orifice tip that is screwed into the spa jet. Mostly found on inground spas, Nozzles of different sizes can be replaced. For portable spas and hot tubs, common spa jet nozzles are part of the one-piece Jet Internal.


Water leaving a spa or hot tub. Spa Suction Outlets include the spa skimmer and spa main drain, aka spa suction outlet. Outlets are where the water goes Out of the tub, and Inlets are where the water comes In to a hot tub.


Printed Circuit Boards, or Spa Circuit Boards, often abbreviated PCB's are used in every spa controller and topside control. Modern spa controls depend heavily on PCB's, which have improved in quality and design tremendously in the last 20 years.

Pressure Switch:

Pressure Switch for spas is used as an approximation of water flow, or used in place of a flow switch. Pressure switches are factory set to open when they sense a minimum level of pressure within the heater, as an indicator of sufficient water flow for safe heater operation.


The spa or hot tub pump is the heart of your circulation system, crucial for filtration, sanitation and heating. Some spas will have one 2-speed pump, and others will have 2 pumps, one for 'Jet Action' and one for near constant circulation.


Spa Relay is an electronic switch, usually mounted to a printed circuit board. They are often small black cubes about an inch tall, and are used to control switching to your spa equipment, or turning on/off your pump(s), heater, blower, light, ozonator.

Shut-off Valve:

Also called an Isolation Valve, Spa Shut-Off Valves allow you to shut off the water to perform certain maintenance items like cleaning the pump basket or spa filter, adding chemicals, or making repairs to the spa pack or other equipment.


Surface Skimmer is the full name, a spa skimmer is used to draw water from the surface to remove floating debris and dust. Works in tandem with the spa drain, to keep spa water clean and clear. Skimmers have a skimmer Weir and basket to empty.

Split-Nut Union:

A Split Nut Union is a Lock Nut with two small screws on either side. Most often used to replace a broken Lock Nut, because there is no way to slip a new one over the pipe. Split Nut Unions come apart to quickly replace pump unions and heater unions.


A Tailpiece is half of a spa union, specifically half of a Pump Union or Heater Union. It's the part that slips through the Lock Ring and connects to the incoming or outgoing pipe. Can be ordered separately or as a pump union or heater union part.

Temp Sensor:

Temperature Sensor is the full name, used to monitor temperature of the water, both for display on the topside control, or for use to prevent overheating. New Style M7 Balboa heaters have done away with pressure switches and instead now use two temp sensors.


There are terminals all over your spa control and equipment. Any place that a wire makes a connection, there is a terminal. Spa wires use many types of plugs but they all connect to some sort of terminal. Keep your terminals clean and dry.


Older spa control systems use mechanical thermostats, but most spas on the road nowadays have electronic thermostats used with a temperature sensor, placed into a thermowell, to sense the current water temperature, and allow user adjustment.


Thermowells are the holders or 'well' of a temp sensor. Dry thermowells are a metal or plastic tube in the shape of a test tube, with the temp sensor placed inside. Wet thermowells are simple rubber seals that allow placement of a heavy duty coated temp sensor in direct contact with the spa water, inside of a pipe.


Spa and hot tub timers control the operation time for pumps to run each day. Modern spas allow you to choose from modes, but older control systems use mechanical timeclocks to set program times. For most spas, 12-18 hrs daily on low speed, and 1-2 hours on high speed is sufficient.


Spa Transformers reduce voltage from a higher voltage to a lower voltage. Spa controls all have a transformer to operate the spa systems with just 24V-32V usually. Transformers for spas can be tested with a multi-meter, voltage-in and voltage-out.

Topside Control:

The main spa control panel mounted on the 'Top Side', for user control of program modes. Also known as a spa side control, or display panel, it functions as a remote control panel to your spa controller. New Topside Panels must match the Spa Control model exactly.


Unions are used to facilitate easier removal of spa equipment from tight spaces beneath spas. Pump Unions and Heater Unions can often be removed with big hands, or a strap wrench or large Channel pliers may be needed for sticky unions. Union parts include the Tail Piece, Lock Nut, O-ring and Male End.

Vacuum Switch

A Vacuum Switch is the opposite of a Pressure Switch, but it operates in the same manner, as a proxy for water flow. Vacuum Switches are placed in front of the suction side of the pump, factory set to open when they sense a minimum level of vacuum pressure.


The Venturi Effect was first documented by Giovanni Battista Venturi way back in 1797, and the principles in use today are still the same. Fluid pressure reduces when water is forced through a small opening. Mazzei ozone injectors use the venturi principle, as well as passive Air Controls.


Pump Volutes are also called the pump strainer housing or more specifically the pump impeller housing. The shape and design of the pump volute determines the flow characteristics. Volutes are fairly sturdy but may crack under extreme pressure or freezing water.

Wall Fitting

Spa Wall Fittings is the beauty ring or trim ring around a spa jet, typically round and open in the center with threads on the inside and/or outside. Wall Fittings are often available in designer finishes and colors.


Inside of every spa skimmer is a tiny flapper door thingy, called a skimmer weir or floating weir. Packed with foam, the spa weir has two purposes, to accelerate water flow into the skimmer, and to stand vertical when the pump shuts off, to trap debris inside the skimmer well.

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Leslie’s makes every effort to provide accurate recommendations based upon current ANSI/APSP/ICC-5 2011 (R2022) standards, but codes and regulations change, and Leslie’s assumes no liability for any omissions or errors in this article or the outcome of any project. You must always exercise reasonable caution, carefully read the label on all products, follow all product directions, follow any current codes and regulations that may apply, and consult with a licensed professional if in doubt about any procedures. Leslie’s assumes no legal responsibility for your reliance or interpretation of the data contained herein, and makes no representations or warranties of any kind concerning the quality, safety, or suitability of the information, whether express or implied, including, without limitation, any implied warranties of merchantability or fitness for a particular purpose.