Welcome to Backyardplus! In this post, we show you how to troubleshoot high limit trip on a hot tub, otherwise known as protection mode. When the spa goes into high Limit trip, the red power light or blue logo light starts to flash, indicating a high limit condition, making the heater and jet pump inoperable. Before we get started, let’s go over the tools and parts you will need.

Tools you will need:

• Phillips head screwdriver
• Small towel or rag
• Multimeter

Parts you may need:

• 79005 High Limit Thermistor
• 74427 E5 Circulation Pump
• 73178 Tri-X filter

1. High Limit Thermistor Plugged in Incorrectly:

If you just bought new sensors and installed them, and the power light is flashing, check the connector and make sure the high limit thermistor is plugged into the two pins on the motherboard correctly. If you’re off by one pin, the power light will flash. If this does not apply, move to the next step.

Disconnect the power.

Plug in the high limit thermistor correctly.

2. Clogged Filter:

A flashing power light can be caused by a dirty filter. Remove the filter from the gray standpipe and see if the power light quits flashing. If the power light stops flashing, you simply have a clogged filter. Clean or replace the filter. If this does not apply, move to the next step.

3. Air Lock:

An airlock will cause the power light to flash. If you recently drained and refilled the spa, you may have an airlock. An airlock happens when air gets trapped in the circulation pump line. To remove an airlock, place a garden hose in the standpipe fitting and hold a rag around it to force all the air out of the line. If this does not apply, move to the next step.

4. Bad Circulation Pump:

A bad or weak circulation pump will cause the power light to flash. You should be able to see movement on the surface of the water. If not, place your hand on the pump to see if it is vibrating. If it’s not vibrating, check the voltage. You should have 110-120 volts. If the voltage is good, replace the pump. If there is no voltage, make sure the summer timer is turned off. If the summer timer is off, check the circ pump fuse. If the fuse is good but still has no voltage, replace the motherboard.

5. Bad High Limit Thermistor (sensor):

A bad high limit sensor will cause the power light to flash. Test the sensor by following the steps below and referencing the resistance vs temperature chart.

a. Set the meter to 20K on the OHM scale.

b. Record the temperature of the spa water.

c. Disconnect power from the spa.

d. Unplug the thermistor from the control box.

e. Meter across the two Thermistor leads.

f. Refer to the Temperature versus Resistance chart below to find the correct resistance value for the temperature measured. If the temperature and resistance does not match that of the chart, this test has failed, and the thermistor must be replaced. Remember if the spa has been inactive, the spa water temperature may be different than the water temperature in the heater housing.

6. Bad Heater:

A bad heater will cause the power light to flash. Run your hand alongside the output tube of the heater. If you feel a spot that is extremely hot, you are most likely dealing with a bad heater. To test the heater: Turn the heater circuit off and see if the spa still goes into high limit trip. If it doesn’t, then you have a bad heater.

7. Cold Water Startup:

If the water temperature is below 55 degrees, the power light will flash. The easiest way to get the spa started is with an extra set of sensors. Place them in a cup of warm water and plug them into the motherboard to trick the tub into thinking that the spa water is warm. If you don’t have extra sensors, you can place a hair dryer directly onto the sensors for 5 to 10 minutes. It should get the sensors warm enough to start the spa and stop the flashing power light. Hot Spot tubs can use the 79005 and 79006 sensors to trick the spa into heating. You cannot use the Hot Spot sensors because both must be in the warm water at the same time.

8. Bad Multicolor Light (2001-2009.5):

A bad multicolor light will cause the power light to flash. If you open the control box and notice the CONTROL UNPLUGGED light is on, the power light is flashing, and water leaking around the light lens, turn off the power to the spa and unplug both light connectors (LED Spa Light, and the I2C Interface). Reconnect power to the tub. If the power light quits flashing and the CONTROL UNPLUGGED light turns off, then you have a bad multicolor light. Currently, there is no replacement option for the 2001-2009.5 Multicolor light.

9. Voltage Spike:

If you had a lightning strike, power surge, or if you were running your spa on a generator, it can take out your motherboard and topside control, and it will cause your power light to flash. If you have good voltage coming into the spa but no lights on the motherboard, it means you have a dead board. You must replace the motherboard and the topside control panel at the same time.

Watch the video here! Red Power Light or Blue Logo Light Flashing? How to Troubleshoot High Limit Trip on a Hot Tub

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