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hot tub not heating troubleshooting

If you’ve recently noticed that your hot tub isn’t heating up quite how you like it to, then you might have some trouble with the heating components. The good thing is, you’ve come to the right place. Hot tubs are supposed to heat up to 104 degrees Fahrenheit, and if yours is not, you likely have a problem.

If you don’t have any error codes present on the display panel, we’ll show you how to diagnose the problem on your own. Here are a few reasons why your hot tub might not be heating.

Your thermometer may be broken, giving you an inaccurate idea of where your hot tub temperature actually is.

Thermometers aren’t necessarily the most precise instruments out there, and while they can provide you with a pretty good reference as to how hot your hot tub is, they may not always be calibrated perfectly to give you an exact reading.

Even if you have a digital display that acts as the thermometer for your hot tub, it could potentially be off by a few degrees.

You Need To Replace Your Cover

If you buy a budget spa, then you might have a problem with your hot tub cover, as it might not be able to provide the same heat maintaining efficiency as a higher-end spa. A dense and thick hot tub cover will do the job much better, and you can find the best ones at The Cover Guy Reviews.

In fact, some of the best covers out there can have an R-value that is three times greater than the value of a basic spa cover.

As your cover gets older, you may find yourself with a waterlogged hot tub cover. it will likely start to take on the water from your hot tub, sagging in the center. The edges of your cover might even begin to tear along the folds or the edges. The good news is, you may not need to buy a 

brand new one, as it could be possible that DIY hot tub cover repairs could do the trick as well as save you some cash. If you can’t see any obvious rips, look for steam that pours out of the sides of your cover when your spa is on. Even this small amount of steam can make it so that your hot tub isn’t able to reach full temperature.

It is very important that you keep the cover on your spa while it is heating up. If you don’t, the heating element won’t be able to perform to its fullest. You may even consider using a floating spa blanket if you want to trap the heat in your hot tub water a bit more.

Temperature Is Low Outside

Some spas simply cannot overcome temperatures that are extremely low. When it comes to portable 110v hot tubs, otherwise known as “plug-n-play” spas, the spa heater might simply not have the strength to overcome heat loss from low temperatures. 

The same thing goes for hot tubs that don’t have tons of insulation built into them or those that have small heaters. Some spas have small heater elements. This would be considered anywhere under 4 Kw or 4,000 watts. The less that you pay for the spa, the more likely it will have trouble getting and remaining hot when temperatures are low outside.

One of the best ways that you can combat this is by using a high-quality spa cover or some type of floating spa blanket. You can also improve the insulation on the underside of your spa or wrap the outside of your hot tub to keep it safe from lower temperatures. For more ideas, see our how to insulate a hot tub article.

If your hot tub has a small heating element, you may consider upgrading to a larger one if possible.

Broken Temperature Sensors

Most modern hot tub models make use of high-limit switches and electronic temperature sensors, which are made to check the temperature in your spa on a consistent basis. This type of technology has the ability to check both the inside temperature and outside temperature of your spa. You will find all of this wired to your main control panel.

If this is one of the problems, you’ll need to do some hot tub temperature sensor trouble shooting. More often than not, there will be an error code on your control panel that will tell you what to do. This is especially true if the temperature sensor is causing your hot tub heater to shut down. A temperature sensor or thermostat can shut your heating element down if it is off by a few degrees, as it will believe that your spa is hotter than it actually is.

Problems With Air Blower

If you keep the air intake knobs open all the time or use a forced air blower to keep your water cool, then the water will always be much colder than what the temperature is telling you.

If you notice that you have problems with your spa heater during cold weather bouts, then you might want to turn off the blower.

Hot Tub Heater Isn’t Running For Long Enough

It is important to remember that hot tubs often take a while to heat as it is. There are some hot tubs out there that heat up at the speed of 1 degree Fahrenheit per hour, while many newer and higher-end hot tubs can heat up anywhere from 2-4 degrees every hour. You need to make sure that you set your timer properly so that it has a long enough time to heat up before you get in it. This is especially true if the weather outside is cold.

If you want to speed up the heating process in your hot tub, we highly recommend running the heater and the circulation pump in a continuous manner. Sometimes, the heating process can take up to 24 hours if you want to get it to the optimal temperature.

There are a couple of factors that can impact the speed at which your heating element works, including the size of the spa heater, the efficiency of your spa cover, the air temperature outside, and the water temperature.

Dirty Spa Filter

While we originally said that we’d be covering troubleshooting situations that don’t have error codes, if you have a spa filter that is dirty and that is the reason your hot tub won’t heat, you will likely get some sort of error code. This type of error code will pop up on your control panel if your hot tub’s pressure switch is showing that there is low flow. When that error code pops up, the heating element will shut off.

To remedy this, you can take your spa filter or spa cartridge out of your hot tub to see if the flow begins to improve. If it does, you know that you need to replace the filter. You may also need to reset your hot tub with the heater element button.

When it comes to performing routine maintenance on your hot tub, it is important that you clean out your hot tub filter every four months at the least. You should also replace your filter every 1-2 years to make sure your flow and filtering are running optimally.

You Just Drained and Refilled Your Spa

If you just recently drained and refilled your hot tub, it is important that you run your hot tub heater continuously for 24-48 hours until your water gets to optimal heat. Once your hot tub is completely heated, you can reset your timer so that it runs anywhere four hours to eight hours each day. The amount that you need to run your heater will depend on your particular model, so make sure to consult with the manual.

It is just as important that you make sure your hot tub’s circulation pump is primed. If it is drawing in the air or it is not air locked, you could run into problems. Conditions like these can cause the spa heater to overheat, which will eventually shut it off. If this is the case, the fix might be as simple as hitting the heater element reset button.

Hot Tub Water Level Is Low

If your hot tub water is starting to draw a steady stream of air into the skimmer in the shape of a vortex, or if it has a skimmer door or thermometer stuck that is causing it to gulp down air, the hot tub heater will likely overheat and shut itself off.

If this happens, you might need to hit the reset button on the heater element to fix it.

To keep the water level from dropping too low in your hot tub, you should regularly add water to it.

High Limit Switch

Beyond your thermostat, you have another switch on your hot tub called the high limit switch.

This particular switch is very similar to your thermostat and your pressure switch, which we discussed above, as all of these are part of the system’s safety circuit.

The purpose of the high limit switch is to stop the spa heater from overheating and not shutting off. 

If your heater continues heating and there isn’t a switch like this in place, it could create scalding water and melt the components inside of the spa.

Hot tub manufacturers will calibrate high limit switches so that they trigger at a max temperature. When the hot tub hits this max temperature, the switch will open up and break the electrical circuit on the circuit board that delivers power to your spa’s heater element.

When it comes to high limit switches, one monitors the outside temperature of the spa heater and another that manages the inside temperature of the spa heater. If you have a high limit error, it will most often pop up as an OH code or an HL code. If you have an older spa, it will likely have a small red button that pops out when the hot tub heating limit has hit its max.

One of the reasons that some high limit switches trip is because of low flow, which can cause temperatures that are higher than normal. Other things that often cause tripping in this regard are damaged wires, loose wire connections, malfunctioning elements, and incorrect voltage. If these are the problems that you are dealing with and you are not an electrician, we highly recommend that you call a professional.

Bad Spa Heater Element

A spa heater element is very similar to your typical electric hot water heating element.

If they are operated without being surrounded by cool water, they will burn out fast. 

You can test out your hot tub heating element to determine if you have a short in the surrounding coating.

To do so, you can take a test meter and set it to ohms so that you can measure the resistance of your heater element in your spa. If you have a good element, you will likely get anywhere between 9 and 12 ohms. On the other hand, if you measure it with your test meter and it pegs up at the highest setting, then you probably have a short and will need to replace your heater element.

Spa heater elements are notorious for building up scale from salt water sanitation or hard water. Heater elements that have scale surrounding them will reduce the output of the element. If you don’t fix this in the long run, it could completely ruin the element altogether.

If you don’t know what spa heater elements look like, think of a coil that is on your stovetop. If your heater element’s casing cracks, then you will definitely need a new element. When it comes to locations with hard water, you might consider using a sequestering agent to make sure your alkalinity levels don’t get too high.

For people that have new hot tub models, heating elements will often sit in a thin, stainless steel chamber. Typically, these have unions, making them quite easy to remove. The beauty of these elements is that they are very easy to test because of their easy removal.

When you test your heater with an ammeter or a multimeter, you will get an “open” if the meter on your tool spikes to the high side. When you don’t have any activity on your meter, or if the activity is very little, then you have a short. A short, otherwise known as a “short circuit,” is when the current leaves the circuit.

Additional Reasons

There are a few additional reasons as to why your hot tub might not be heating, many of which you would never think of. If you’ve gone through the above list and your heater is still not working, then it is likely one of these problems. The good thing is, all of these issues can be fixed pretty easily.

GFCI Tripped

Look at your spa pack for the electrical outlet, which has a large red test button on it. If you notice that the red button is popped out, all you, might have to do is push it back in to get your hot tub working again.

Blown Fuse

The circuit board can be destroyed by quite a few things, including incorrect voltage, surge, or a power spike.

Loose Wires

If you notice that your wiring connections are oxidized or not tight, then it could be the reason your heater is not working. Crimped wires, melted wires, and chewed wires from rodents are major culprits for reasons that heater elements stop working.

Door Interlock Is Open

Most hot tubs have a spa cover switch or cabinet switch, which will prevent the operation of the hot tub unless the door is completely closed. If you have this on your hot tub, then a simple closing and tightening of the door might do the trick.

Final Thoughts

Hot tub not heating?

If so, we highly recommend going through the list above to see if you can troubleshoot the problem on your own. A hot tub that is cold won’t do you any good, as hot tubs are meant to be, well, HOT.

There are many things that are quite easy to fix, such as a loose airlock, a broken thermostat, or a low water level. However, there are other things, such as a busted digital control panel, lack of water pressure due to a faulty pump, or broken jets, that you might need to get in touch with a professional for if you need a fix.

Sometimes, you might need to replace the heater altogether. This is especially true with older spas.

Regardless of what kind of spa you have, it is best to take preventative measures so that you can keep your system in good, working condition for many years to come. Make sure that you clean the filter on a routine schedule, consistently check your heater chamber to see if anything needs to be replaced, and fix any problems that arise right away.