Hot tub troubleshooting, as far as heating issues are concerned, is something that can be easily performed. There are a few things that must be checked to find out exactly how serious the problem is and whether it is necessary to call a repairman. If the water isn't heating up but it is circulating, this means that there is a problem with the heating element. But if the water gets too hot, some simple steps will lower the temperature.
Disclaimer: Be sure to disconnect the hot tub before beginning to avoid accidents. It should be mentioned here that you shouldn't work with electricity unless you are comfortable with it, and may consider calling a repairman in this situation. Wear rubber-soled work boots if you are going to troubleshoot the hot tub yourself.
The Filter Cartridge
If the water is heating up but too slowly, replacing or cleaning the filter cartridge will probably solve the problem. Also, if the heater keeps turning on then off, this is also an indication that the filter needs to be changed. The more often the hot tub is used, the more frequently the filter needs to be changed. To do this, consult the manufacturer's guide or find it online.
Simple Measures if the Hot Tub is not Heating
There are some simple things you could try if the hot tub does not heat the water. First of all, open and close the spa door on the spa cabinet, and see if it starts heating. If the hot tub is gas-powered, you should check if the pilot light turned off and turn it back on. Another option is to replace the insulating cover since a damaged cover will affect the heating of the tub.
The High Limit Switch
If the temperature exceeds a certain value, usually 120°Fahrenheit, the high limit switch turns off the heat. This usually occurs if the tub has been recently drained due to the air running through the system. If so, you should let the tub run a few times and it should come back to normal.
Also, find a red button in your spa pack, which is the high limit switch, and reset it. If this switch is constantly tripping, even if you haven't emptied out the tub recently, you should get in touch with a repairman.
The Spa Thermostat
If the water is too warm, check to see if the thermostat has been set too high. You probably have to calibrate the thermostat down. In most models, this can be performed by turning the Allen screw on the thermostat 90 degrees clockwise. If the problem persists, you may have to replace the thermostat.
The Thermal Well
Check if the temperature probe is resting inside the water or is suspended in the air. Consult the owner's manual to find out where the probe is, and push it into the water if it is not in there already.
Also, check the insides of the thermal well for any mineral buildup. If there is a visible buildup, the thermal well needs to be replaced.