Comprehensive Step-By-Step Guide On Replacing Your Hot Tub Heater

A failed hot tub heater can leave you with perfectly circulating water that simply refuses to get warm. Fortunately, replacing many common flow-through spa heaters is relatively straightforward once you have correctly identified the heater and determined that the heater itself is actually the problem.

This guide walks through the basic process of replacing a typical electric flow-through hot tub heater in seven steps. The exact installation varies by spa manufacturer and control system, so always follow the instructions provided with your replacement heater and spa control system.

Before Replacing the Heater: Make Sure You Have the Correct Part

Spa heaters can look remarkably similar even when they are not interchangeable.

Before removing the original heater, identify as much of the following information as possible:

• Manufacturer
• Heater part number
• Control-system manufacturer and model
• Heater length
• Plumbing size
• Kilowatt rating
• Voltage
• Sensor configuration
• Pressure-switch or flow-switch configuration, if applicable
• Electrical connection style
• Mounting arrangement

If the original part number is readable, start with our Heater Finder. It includes current, discontinued, and known replacement information for many spa heaters.

How Do You Know the Spa Heater Actually Needs Replacement?

A spa that is not heating does not automatically have a bad heater.

Other problems can prevent a properly functioning heater from operating, including:

• Insufficient water flow
• A dirty or restricted filter
• Air trapped in the plumbing
• A failed temperature or high-limit sensor
• A pressure-switch or flow-switch problem
• A circuit-board or heater-relay failure
• Loose or damaged wiring
• A tripped high-limit condition
• Incorrect control-system settings

One common heater failure is a dry fire. This occurs when the heating element is energized without adequate water surrounding it. Because the element is designed to transfer heat into moving water, operating without sufficient water or flow can cause the element to overheat and fail very quickly.

If you have not already determined that the heater is defective, diagnose the heating system before replacing parts.

Replace the Complete Heater or Just the Heating Element?

Some spa heaters can be repaired by replacing only the internal heating element, while others are more practically serviced by replacing the complete heater assembly.

Replacing only the element may make sense when:

• The heater tube is in excellent condition
• The correct element is positively identified
• The terminals and mounting surfaces are undamaged
• There is no significant corrosion
• The remaining components are in good condition

Replacing the complete heater assembly often makes more sense when the original heater is older, leaking, heavily corroded, damaged, or when sensors and other heater-mounted components are also aging.

The decision should be based on the condition and design of the heater rather than assuming that replacing only the element is always the less expensive long-term repair.

Tools and Supplies You May Need

The exact tools depend on your spa and heater installation, but commonly needed items include:

• Screwdrivers
• Appropriate wrenches or pliers for the heater unions
• Nut drivers or socket set, depending on the control box
• Wire labels or masking tape and a marker
• Phone or camera for documenting connections
• Replacement heater
• New heater union gaskets or O-rings when required
• Towels or a small container for residual water

Step 1 – Turn Off the Power and Water

Before touching the heater or opening the spa control system, turn off electrical power to the hot tub at the breaker or disconnect.

Do not assume the equipment is electrically safe simply because the topside control panel is off.

If the plumbing has functioning shut-off valves on both sides of the heater, close them to isolate the equipment area from the spa water.

Some spas do not have usable isolation valves. If the heater cannot be positively isolated from the spa water, the water level must be lowered sufficiently or the spa must be drained before the heater is removed.

Step 2 – Drain the Water From the Spa

For the most straightforward and predictable repair, drain the spa before removing the heater.

Use the manufacturer's drain fitting or normal spa-draining procedure and route the water to an appropriate drainage location.

If your particular spa has effective isolation valves that completely isolate the heater and equipment area, complete draining may not always be necessary. However, if there is any doubt about whether the valves will hold, drain the spa or lower the water sufficiently before disconnecting the heater.

Remember that even after draining, some water will usually remain inside the heater tube and plumbing.

Step 3 – Disconnect the Heater Power

With power disconnected and the water isolated or drained, locate the heater's electrical connection.

The connection varies considerably by control system. A heater may use:

• A plug-style connector
• Direct terminal connections
• Short copper or metal terminal straps
• Manufacturer-specific heater connections

Do not assume that your spa will be wired exactly like another model.

If the heater uses a plug, carefully disconnect the plug without pulling directly on the wires.

If the heater is hardwired, photograph and label every connection before removing anything. Reconnect the replacement exactly as required by the heater and control-system manufacturer.

Also note any grounding or bonding connection associated with the heater.

Step 4 – Remove the Old Spa Heater

The heater is normally connected to the spa plumbing by large union nuts on each end.

Before loosening them, place towels beneath the heater because residual water will normally remain inside the tube and plumbing.

Try loosening the union nuts carefully. If a tool is necessary, use an appropriate wrench or large pliers with care.

Do not crush, crack, or distort the plastic union nuts or plumbing fittings. Avoid applying unnecessary force to the PVC plumbing.

Once both unions are loose:

• Disconnect any remaining sensors, pressure switches, grounding connections, or mounting hardware as required.
• Support the heater while removing mounting hardware.
• Separate the heater carefully from the plumbing.
• Remove the old heater from the equipment compartment.

Inspect the Heater Union Gaskets

Once the heater has been removed, inspect the gaskets or O-rings that seal the heater unions.

Replace them if they are:

• Cracked
• Flattened
• Hardened
• Torn
• Distorted
• Missing

Reusing a worn heater gasket is one of the easiest ways to create a leak immediately after replacing the heater.

Step 5 – Install the New Spa Heater

Before installing the replacement, compare it carefully with the heater you removed.

Verify:

• Part number or confirmed replacement relationship
• Overall heater configuration
• Plumbing size
• Heater length
• Kilowatt rating
• Electrical configuration
• Sensor or pressure-switch arrangement
• Mounting points

Clean the sealing surfaces and make sure no debris has fallen into the open plumbing.

Position the new heater in the same orientation as the original and make sure the union gaskets are correctly seated.

Start the union nuts by hand. They should thread smoothly without excessive force. If a union immediately becomes difficult to turn, stop and make sure it is not cross-threaded.

Tighten the unions evenly and according to the heater or equipment manufacturer's instructions. Over-tightening plastic union components can crack or distort them.

Step 6 – Reconnect the Heater

Reconnect the replacement heater using the photographs and labels you made before removing the original.

Depending on your equipment, this may include:

• Heater power connector
• Hardwired heater terminals
• Temperature sensors
• High-limit sensors
• Pressure or flow switch
• Ground or bonding connection
• Other heater-specific connections

Make sure connectors are fully seated and wiring is routed away from sharp edges, moving equipment, and hot surfaces.

If the control box was opened, reinstall and secure the cover before restoring electrical power.

Step 7 – Refill the Spa, Establish Water Flow and Restore Power

This is one of the most important parts of the entire replacement.

Do not energize the heater while the heater tube is empty or before adequate water flow has been established.

First:

1. Make sure all drain fittings are closed.
2. Open any heater or equipment shut-off valves that were closed.
3. Refill the spa to the manufacturer's normal operating level.
4. Inspect both heater unions for leaks.
5. Prime the circulation and/or jet pump according to the spa manufacturer's procedure.
6. Make sure air has been removed from the plumbing.
7. Confirm that water is circulating normally through the system.

Only after the spa is full, valves are open, the plumbing is primed, and the equipment is ready for normal operation should electrical power be restored.

After Restoring Power: What Should You Check?

Do not simply close the equipment compartment and walk away.

Watch the system during its initial operation.

Confirm:

• The pump has established normal water flow.
• There are no leaks at either heater union.
• There are no leaks around sensors, pressure switches, or other heater fittings.
• The control system does not display a flow, sensor, or heater error.
• The heater begins operating normally when heat is requested.
• No unusual odor, sound, arcing, overheating, or electrical behavior is present.

Remember that a hot tub does not become hot immediately. The water temperature should gradually rise as the spa operates normally.

What If the New Heater Still Doesn't Heat?

If the replacement heater is installed correctly but the spa still does not heat, do not automatically assume the new heater is defective.

Check for other problems such as:

• Insufficient water flow
• Dirty filter
• Air lock
• Closed or partially closed valves
• Temperature-sensor problem
• High-limit condition
• Pressure-switch or flow-switch problem
• Control-board heater relay problem
• Incorrect system configuration
• Power-supply problem

A heater can only produce heat when the control system supplies the proper power and the system's safety conditions allow it to operate.

What Causes Spa Heaters to Fail?

Heating elements eventually fail, but premature failure often has an underlying cause.

Common contributors include:

• Dry firing
• Low water flow
• Running with closed valves
• Extremely dirty filters
• Scale accumulation on the heating element
• Improper water chemistry
• Corrosion
• Electrical connection problems
• Failed relays or controls
• Normal age and repeated heating cycles

If an old heater failed unusually early, try to determine why before installing another one. Otherwise, the same underlying problem can damage the replacement.

Finding the Correct Replacement Spa Heater

The manufacturer's number printed on the old heater is usually the best starting point.

However, many older heaters have been discontinued or superseded by newer part numbers. A discontinued original number does not necessarily mean a replacement is unavailable.

Need Help Identifying Your Heater?

If you still cannot determine which heater you need, give Bath & Spa Parts Online a call at 800-918-9143.

When contacting us, having the following information ready can help:

• Original heater part number
• Spa control-system manufacturer and model
• Heater length
• Plumbing size
• Kilowatt rating
• Photos of the heater
• Photos of the heater label
• Photos of the electrical connections
• Photos of the sensor or pressure-switch arrangement

We have been helping customers identify and replace difficult-to-find pool, spa, bath, and hot tub parts for more than 45 years, and sometimes a few good photographs are all it takes to determine what you have.

This guide provides general information for common electric flow-through spa heaters. Heater installation and electrical requirements vary by manufacturer, model, control system, and local electrical code. Always follow the instructions supplied by the heater and spa manufacturer. High-voltage electrical work should be performed by a qualified professional when appropriate.