Wiring diagram illustrating typical hot tub or spa heater safety controls (C) Hot Tub, Spa, Whirlpool Bath Heater Repair
Diagnosis & Repair of Spa / Hot Tub & Whirlpool Bath Heaters

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Hot tub & spa or whirlpool bath use, maintenance, troubleshooting & repair:

This article describes the operation, controls, & troubleshooting of heaters used in hot tubs, spas, whirlpool tubs & Jacuzzis.

In these articles we describe the use, operation, maintenance as well as common problems, troubleshooting, & repair suggestions for hot tubs, spas, and whirlpool baths. We discuss hot tub leaks, broken hot tub or spa jets, hot tub or spa water temperature & heater repair, hot tub or spa pump diagnosis & repair, hot tub or spa filter maintenance, cleaning & repair, noisy air pumps at hot tubs, noisy water pumps at the hot tub or spa, and other hot tub, spa or whirlpool bath diagnosis & repair topics.

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Spa Heater Troubleshooting & Repairs

Heat Wave II Hot tub / Spa Heater Control (C) Daniel Friedman

Here is a 20+ year old Heat Wave II electric heater for a spa or hot tub showing the main controls. Newer digital heater units will have similar features.

[Click to enlarge any image]

Below are two more key features of most hot tub or whirlpool tub heaters:

  1. Spa heater on light (green arrow) indicating that the spa heating elements are working and
  2. Spa heater thermal overload reset button / switch (blue arrow). If the spa heating elements are OFF try pressing the heater overload reset switch through the rubber button (that's to keep you from getting fried).

Heat Wave II Hot tub / Spa Heater Control (C) Daniel Friedman

Watch out: do not keep pressing the reset-switch repeatedly. If the system keeps switching off, find and fix the problem. Otherwise the system maybe unsafe.

Watch out: GFCI (Ground fault circuit interrupter) protection should be provided on all hot tub, spa, and pool electrical circuits to reduce the chances of fatal electrical shock.

Troubleshoot a Spa or Hot Tub Heater That's Not Working Properly

If your hot tub or spa heater is not heating at all check that it has electrical power, and check that its indicator light is on [Green arrow in our photo just below].

Heat Wave II Hot tub / Spa Heater Control (C) Daniel Friedman

The Heat Wave II hot tub / spa heater shown above was produced by

Most spa heaters will include a thermal overload reset switch [Blue arrow in our photo above]. To protect the spa heater or hot tub heating elements from damage from overheating, this switch will turn OFF the heater if its internal temperatures become too high. A common cause of excessive temperatures in the spa heater and thus of its constant tripping of the thermal overload switch is inadequate water flow through the unit.

For the hot tub heater shown here, Heat Wave notes in the unit's instructions (you kept those, right?) these important points about water pressure and heater operation:

  1. Required water flow rate: The filter must be kept clean enough to keep water flow rate (provided by the spa pump) above15 gallons per minute (GPM). If system pressure drops below this level the pressure switch will drop out (turn off) and the hot tub heater will turn off or become inoperative. Incidentally for this heater unit the maximum flow rate in GPM is 60.

    Basically, anything that slows the water flow rate may prevent the heater from staying on: clogged piping, clogged filter or strainer, a valve that's closed, a damaged pump impeller, excessive air in the system from air leaks on the suction lines, etc.
  2. Required operating system water pressure: A pressure sensing switch inside the heater unit is set to 2 psi. If water pressure falls below this limit the heater will turn off. If your heater is located below the level of the spa this switch may require adjustment for proper heater operation.
  3. Maximum heater output water temperature: a high limit thermostat is set to 140°F.

    Watch out: Keep in mind that in a spa or hot tub the maximum safe water temperature is 104°F - much cooler.
    Also see this article on SCALD PROTECTION at plumbing fixtures.

Wiring diagram illustrating typical hot tub or spa heater safety controls (C)

Watch out: in returning the hot tub to operation and to keep the heater working for the hot tub illustrated in this article we needed to run the pump at high speed. But before the pump would operate successfully at high speed we needed to take several steps:

Leaky spa filter cap is evident by the white deposits (C) Daniel Friedman

Above: when we first turned on the spa pump this Hayward filter leaked like mad. The white deposits all over it indicated a history of leaks when the unit was last used. We removed the filter cap and found that it was cracked.

  1. Fill the hot tub or spa above the jets. Until you put enough water into the spa to reach above the jets you cannot operate the pump - you won't know if the spa or its piping or fixtures are leaking or not. Unfortunately when you find leaks you'll probably have to drain the spa below the level of any parts to be removed or repaired.
  2. Fix leaks anywhere in the system. At the filter, leaks due to cracks in the filter top were squirting water everywhere. It may be possible to repair cracks and small leaks at the filter using epoxy, taking care not to obstruct air bleeder holes and threads for the filter air bleed screw. Otherwise such parts need to be replaced.
  3. Clean the spa filter: if the spa filter is clogged the pump may not reach the required flow rate to operate the spa heater. Hayward filters can be removed and washed with warm water and a garden hose with spray attachment. Don't try a car wash high-pressure sprayer or you'll ruin the filter. If the filter or its sealing gaskets are torn or damaged, replace it.
  4. Fill the spa or hot tub to its upper water intake level. If the water level is below the upper pump intake port air will be drawn in to the port, the pump will cavitate, it will be very noisy, and it will not pump water properly. In turn this may keep the spa heater from operating. See the photo just below.

Spa or hot tub required water level (C) Daniel Friedman

Above: required water level in the hot tub or spa: must be over the upper spa water intake port that in this installation is hidden behind the vertical plastic cover. Otherwise at high speed the spa pump will draw air, cavitate, and fail to pump properly. When cavitating or pumping air, the pump will also be as noisy as all get-out.

Inside the Whirlpool Heater Control Box

Below: a peek below the top cover of this whirlpool tub heater control shows us several key components:

Whirlpool tub heater control interior components (C) Daniel Friedman

Whirlpool Tub Heater Trips Thermal Overload & Water Won't Get Hot Enough

At the time of our inspection (March 2016) this whirlpool tub would not heat satisfactorily, shutting its heater off by tripping the thermal overload switch at about 95°F.

Earlier we noted that inadequate water flow rate can trip the pressure switch causing the tub to fail to heat. The pressure switch is there to prevent burn-up of the heater element - a condition that would occur if the heater were switched on and the pump was not circulating water or if there was no water or not enough water in the tub. On this whirlpool tub the temperature control and sensor are sold as a unit and the device has been replaced at least once before: below is an old temperature control and sensor found under the tub.

Whirlpool tub heater temperature sensor & control (C) Daniel Friedman

On this whirlpool tub heater unit we suspect that the temperature sensor or its relay is the problem.

While our repair service tech opined that the system is beyond economical repair, if we can swap in a new temperature sensor for $50. or less in parts (and free labor from the author) this repair might be worth trying.

Aquastat immersion well  sensor details, adapted from Honeywell's L7224U universal aquastat installation instructions cited in this article series (C) InspectApedia 2015

As we learned with heating boiler aquastats (AQUASTAT TROUBLESHOOTING), something as simple as poor thermal contact between the temperature sensor bulb and the sides of the well into which it inserts can be enough to cause thermostatic controls to malfunction.


Continue reading at SPA / HOT TUB INSPECTION & CODES, or if your spa or hot tub needs repair see SPA HOT TUB WHIRLPOOL REPAIRS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.






Or see these

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