Cold Hot Tub

How To Fix A Hot Tub That Won’t Heat

If your hot tub won’t heat up there are a number of steps to take to fix it. While you may be able to do this at home we advise hiring a qualified repairman to do it right. Fixing a hot tub that doesn’t heat up can often times be a simple fix, but be it the switch trip, the coils, or the heating element you don’t want to tamper with electricity, especially when water is involved. With that said, here are step by step instructions that you or your professional service team can follow to take your broken hot tub from a cold spa back to a heated solution.

These steps will help you determine why your hot tub wont heat up, and how to fix it.

  • Step 1 
    Hi Limit Switch Trips (Heater Re-set Button)

Assuming that everything else is working properly (i.e. spa is set in the heater/filter cycle and water is flowing from the jets), the first thing you will look for is the Hi-Limit Switch, also referred to as the heater reset button. Now finding it can sometimes be a problem, it’s as if it was purposely put it in a hard to find place, especially in some of the older spas. This is why the hi-limit switch has been pictured below. NOTE: If you have a circuit board you will not see this hi-limit, please see the blue notes above to refer to “circuit board troubleshooting”.

Circuit Board Tester For Hot Tubs

What you are looking for is that red button that is pictured above; it is the only actual part of the hi-limit switch that is visible without going inside the control boxes. When you locate it, give it a push, if you feel or hear a click, or you see a heater indicator light come on that wasn’t’t on before, then you have solved the problem.

It is highly recommended scrolling down to the section that explains why the hi-limit switch trips.

NOTE: Pictured below is a typical “hard to find” place you may find the hi-limit switch installed. The red button is not visible in this case, but is behind a rubber boot.

Hi Limit Switch For Hot Tub

IMPORTANT: Some spas have the thermostats located on top. These are called Spa Side Controls, they have built in air buttons and orange indicator lights. One of the indicator lights says heater, this light comes on regardless if the spa is heating or not. Do not troubleshoot using this light, it could confuse you.

  • Step 2 
    Why Does The Hi Limit Switch Trip?

The #1 reason is filter related. It has become old, dirty or clogged, which has restricted the flow of the water. This fools the hi-limit switch sensor into thinking that the spa water is getting to hot. This is what a hi-limit switch does. It’s a safety switch that measures water temperature, tripping if it senses a higher than normal heat rise.

A good way to check if the filter is causing the hi-limit switch to trip, is to run the spa without the filter for a couple of days. If the hi-limit switch does not trip, then it is time to buy a new filter. (See Filters)

Another reason the hi-limit switch trips is for the very reason they were designed; the spa water exceeded an abnormal temperature rise – Refer to Water Gets Too Hot section.

The final thing it could be, without getting further complicated, is the hi-limit switch is faulty and needs to be replaced.

Other things to look for:

Are all the jets open to allow maximum flow? Are the shut off valves open all the way? Is there enough ventilation where the equipment is? (Can equipment breathe?) Is there water coming out of the jets at all? (See STEP 3 paragraph (5) referring to “Air Locks”.)

FINAL NOTE: Before you drain your spa, turn down the thermostat! By not doing this can cause the hi-limit switch to trip. If pushing or replacing the hi-limit switch has still left you without heat, then proceed on to the next test.

  • Step 3 
    Checking The Heating Element Using A Multi-Meter And Amp Meter

Assuming that the heater/filter cycle is running, the thermostat is turned all the way up and you see water flowing out of the jets; then remove the control box cover and locate one of the wires going to the heating element, usually coming from the contactor.

Open the clamp of the amp meter and wrap it around the ONE wire you chose. With the power and heater/filter cycle on, you should be reading approximately 15 amps on a spa that is wired 110 volts, and 25 amps on a spa that has been wired for 220 volts. If you are getting either one of these readings, then the heating element is working properly. Spa water heats at a rate of 3 degrees an hour wired at 110 volts and 10 degrees an hour at 220 volts. If you did not get a reading at all then continue with next test.

Make sure that the heater/filter cycle is on, and the thermostat is turned all the way up doing this test. Using the multi-meter or the amp-meter with the selector on voltage AC, take one lead from the meter and place it on one of the heater element post. Then take the other lead and place it on the other post. If your spa is operating as a 110 volt system, then this is what you should be reading on the meter, if it is a 220 volt system, then that is what you should be reading. Below is the most common element (Flo Thru) used in the industry, however the rules above apply to ALL elements.

Tool to Measure Voltage in Hot Tub Heater

Now, if you did the amp test and had no reading at all, then, you did the voltage test and HAD THE PROPER reading you have solved your problem. Replace the heating element. Find “Heating Elements” in the parts section.

  • Step 4 
    When Testing The Element For Voltage Or Amperage I Find Know Readings.

Find the two wires that feed the heating element coming from contactor (. With the spa in the heater/filter cycle and water flowing from the jets, watch the contactor that is feeding the heating element while you turn the thermostat dial up and down.( This may require two people.) The contactor should be closing and releasing as you do this, if it is not, then go on to the next test. MORE IMPORTANT “CONTACTOR” INFORMATION BELOW!


Hot Tub Pressure Switch

TIP: Before removing the wires spray some WD-40 on the connectors they are attached to, to prevent the fragile micro-switch from breaking. Then, carefully pull them off.Locate the pressure switch pictured above to help identify it. Once you have located it, remove both wires that are connected.

Once they are removed, tape them together; turn the thermostat dial down to the off position, and turn the power back on. Make sure the spa is on the heater/filter cycle and water is flowing from the jets, turn the thermostat dial up while watching the contactor, if it closes when doing this, then re-test the heater using the amp-meter. If you get 15 amps at 110 volts and 25 amps at 220 volts, then one of two things could be wrong. Either the pressure switch needs replacing or the filter is old, clogged, or dirty.

Put the wires back on the pressure switch. Run the spa without the filter, if you see the contractor close and you have the proper readings at the heating element then you’ve solved the problem (Replace the Filter).

If removing the filter didn’t solve the problem, then the pressure switch should be replaced. See Pressure Switch.


In order for a contactor to close it must have power to the coil, this power is usually traced through a series of components i.e., thermostat, hi-limit and pressure switch. If for any reason one of these components fail then the required voltage to the coil will be jeopardized and the contactor will not close in order to send power to the heating element. As mentioned above, it is usually one of these components that will cause a spa not to heat. Occasionally a contactor will fail, meaning it will have the required voltage at the coil (see below) but will not close. Below are the most common contactor’s and their coil placements. The same rule applies when testing a coil as with a heating element. You must put one lead of your meter on each post/terminal of the coil. If your contactor is 120 volts (see coil info on the side of contactor) then this is what you should be reading, the same applies for 220 volts

Hot Tub Coils

Mentioned above are just some of the basic steps in solving the “no heat” problem and in no way covers all the “could be’s”. Some other things to check are:

  • Faulty heater Contactor
  • Burnt wires
  • Fuses and/or breakers at spa or house
  • Faulty thermostat

These tips brought to you by Spacare, you go to place for hot tub parts and supplies.

If all else fails and you need a quote on a new hot tub, we can help!


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