Why does my outdoor spa hot tub only heat up to 84°F?

The goal of a house owning family to buy an outdoor hot tub is a consistent and comfortable spa atmosphere, usually a temperature of 38°C-40°C approx 100°F–104°F during a cold winter or after an exhausting day. On the surface of things a outdoor whirlpool spa hot tub seems a very simple machine, but a lot of problems can emerge. For example when water heater is on the unit is running, there is no change in the water temperature at 84°F (approx. 29°C), and the user wonders if a product defect has occurred or a heater problem or control system malfunction.

Actually, an outdoor hot tub stalling at 84°F does not necessarily mean the equipment is broken. After-sales data from the outdoor spa industry has shown that the reasons for this phenomenon are very complex and can be due to control setting system, filtration circulation problems, inadequate water flow, heater status, water temperature sensor malfunction, wrong power supply set-up, or even the outdoor ambient temperature. Statistically speaking failures of the equipment itself are less frequent than you could expect, whereas many of the reported "malfunctions" simply come from lack of maintenance, the installation in inappropriate environments, or safety lockout activation.

This article tries to answer the question "Why the hotwater pool outdoors stops at 84°F?" by looking into the working principles of the device, the usual reasons for this problem, how to troubleshoot, and maintenance ideas. All this is done with the aim of helping the users to quickly locate the problem and implement the correct solution.

What does a water temperature of 84°F mean for an outdoor hot tub?

84°F is roughly 28.9°C. Such temperature would be very pleasant water temperature for a swimming or recreational pool, but it is still a good way too below the typical set point range of a home jacuzzi outdoor spa hot tub of 100°F to 102°F (approx. 38°C to 40°C), with some of the brands having a maximum setting of 102°F or even higher. This means that the constant hovering around one of the temperatures 84°F indicates that the heating system was initially working to maintain a warmer temperature but now has come to a restriction point for some reason.

Several outdoor whirlpool spa hot tub owners have shared their experience that when they initially filled the tub water they found that temperature was already 80°F to 85°F and the heat rate dropped afterwards so drastically - or didn't show any appreciable increase - that they gave upon after a few hours of waiting. This can either mean that the heating system has been hindered somehow or that some safety feature (e.g. the protection mode has been activated) is keeping heat from reaching the target temperature level in the first place.

On the other hand, if there's something wrong with the sensor or a safety device has been triggered in the heater unit, the system automatically stops the heater and/or limits its operation. Therefore, in this case, hot water staying at 84°F is an indication of safety system activation, not of a device malfunction.

Reasons Why A Hot Tub Outdoor Stops Heating At 84°F

1. Heating function not selected correctly

Getting to know all the modes is one of the most common pitfalls for first-time outdoor whirlpool spa hot tub owners. Besides basic modes like Standard and Economy, you'll usually find a Sleep mode as well. The heat settings also differ between modes. The Economy mode would heat water mainly during filtration periods while leaving the heater off at other times, even if the temperature setting is higher than that of Economy. On the other hand, the Sleep mode lowers the heater set temperature further so that it may not even exceed 80°F, thereby saving energy to some degree.

One might be tempted to conclude that the outdoor whirlpool spa hot tub isn't working properly after noticing that it stays at 84°F. To prevent such a mistake it is best to check the operating mode that currently is displayed on the control panel - maybe the economy or the sleep mode has been set by accident. Hence, in case of a water temperature that seems fixed at 84°F your first action will be the verification that you did choose the correct mode - if you picked Economy and you want it to be heating continuously you'd need to switch it to Standard mode.

2. Low water flow sets off the safety protection

Pretty much every modern jacuzzi outdoor spa hot tub will have a flow or pressure switch that prevents the heater from activating unless there's a specified level of water flow. A flow that is not sufficient would cause a number of problems namely a totally clogged filter, reduced pump capacity, pipe clogging as well as lack of water up to the min. level required.

When the flow switch fails to detect that water is circulating adequately the control system shuts down the heater automatically as it would be very unsafe for the heating element to be subjected to dry-firing. In this situation, the control panel generally won't show any error message but a water temperature stuck at 84°F will still be an indication of this problem. One of the most common problems leading to this situation is a clogged filter in a unit the filter of which has not been cleaned in a while. For this reason taking care of the filtration part of the system is essential in getting the outdoor whirlpool spa hot tub to work correctly.

3. Inadequate heating and/or operational problems of the heater

The heater serves as one of the main parts that heat the pool water and its output depends on the unit’s size, and its specifications in terms of voltage (e,g., 220,240). If any kind of problem occurs at the level of its core parts, such as the element getting old, heavy scale being added to the surface of the element, relay failure, the actual heater power will drop to a very low level. In this case even the control system is sending the “keep heating” command on a regular basis the heat generated by the heater would be just a fraction of what is needed.

Also, if an outside hot tub that has been left open for heating is situated outside without an insulated blanket and the surrounding weather is cold, that would cause a very large loss of heat from the heater's output - in that case the tub water temperature would stay in the lower 80s degrees Fahrenheit range.

4. Problems with the power supply

Many owners of jacuzzi outdoor spa hot tubs ignore one very important factor when connecting their tubs, i.e. the power supply. For instance, if a hot tub designed for 240V is connected to a 120V line, most elements including control systems and circulation pumps will work but heater will deliver only a fraction of the heat - some outdoor whirlpool spa hot tub models may even restrict heating features to ensure the user is safe.

Plug-and-Play outdoor tubs are very popular in North America as their heating function is much less demanding for a 120V line than for a 240V one. So, the heating time will be roughly double that of 240V units. And when it is the coldest season, the jets and heater cannot be turned on the same time or some units will stop heating to comply with electric codes. Therefore, confirming that the outdoor whirlpool spa hot tub is connected with the voltage that the manufacturer specifies is a significant factor that helps a lot in solving the problem of the water temperature at 84°F.

5. The temperature of the outside air has an impact on how fast the hot tub heats up

What many neglect to take into consideration, however, is the fact that the surroundings have a significant impact on the performance of the outdoor whirlpool spa hot tub and on the speed of the heater. Being exposed to the elements, a jacuzzi outdoor spa hot tub will gradually lose heat via its surface, pipeline, and base if the ambient temperature is equal to or below the freezing (0°C). If the thermal cover was not completely closed or the insulation material has become damaged, then in an hour the heater might not be able to raise the water temperature even a couple of degrees and the whole loss of heat would be substantial!

From what industry data showed there’s quite a difference in heating up an outdoor whirlpool spa hot tub at 0 degrees between a tub with the lid open all the time and the one with the lid closed. The former will lose heat 4 - 5 times faster than the latter, so, if a jacuzzi outdoor spa hot tub is running constantly but the water temperature still doesn't get over 84°F, the heat will actually not stop coming to the water; however, the tub loses as much as the heater produces so it seems as if the heater fails and gives the wrong impression that it can't raise the temperature beyond 84°F.

6. A water temperature meter fault is the reason behind control problems in the hot tub

Hottubs are typically fitted with a couple of temperature meters which constantly measure the water temperature and switch the heating element on and off in response to such changes. If a meter goes out of calibration due to component failure, broken electrical connections between the meter and the unit and mineral deposits on the measuring probe, control unit will get wrong information, and it will shut down. The heater mistakenly determines that the target temperature has been reached and terminates heating at an early stage.

For instance, an outdoor whirlpool spa hot tub can be operating at 84°F of water temperature but due to a malfunction in the meter the water temperature was wrongly read as 100°F so heating operation would stop immediately. This sort of problems usually require that you bring the equipment to a professional shop so they can run tests for you and the temperature meter might very well be the cause that needs to be changed for the system to function normally again.

What steps should be taken to locate the cause of a hot tub not heating above 84°F?

As the outdoor whirlpool spa hot tub is not heating, it would be the fastest way to solve a problem first looking at simple matters and progressively going to complicated ones. Firstly, confirm the setting temperature on the control panel and ensure that the unit is in standard heating mode. Then, check the filtration is working properly and, if necessary, clean or replace the filter cartridge. After that, make sure that the water level is at the height required and that all valves are fully opened. If these tests show nothing wrong, proceed to inspect and replace the electrical power supply if necessary, the fuse status, and also the control panel for any error messages displayed.

If it still keeps at 84°F or so that is the first sign of a problem to contact an engineer to check the parts of heating system including the flow switch, the pressure switch, the temperature sensors, and the main circuit board. This kind of approach helps to spot the problems almost instantly without the guesswork or the replacement of the spare parts.

How can I avoid the insufficient heating problems in my outdoor hot tub?

For the families who use the outdoor whirlpool spa hot tub almost every day or in the weekends it is better to follow the maintenance programme instead of reacting with a quick fix after a breakdown situation. The user is advised to do weekly filter status checks, clean it regularly, and every month perform water quality chemical tests so that the heater remains scale-free. It’s equally important to keep the right water level in the pool for water circulation at its best. Also, a thermal cover that is properly insulated is helpful at reducing heat loss over the winter by keeping the top on. Furthermore, check that the electrical power supply corresponds exactly to the specification of the manufacturer and never change the electrical system to suit your liking as this might put you, the people around you, and most especially your electrical equipment under risk. This kind of regular maintenance not only improves outdoor whirlpool spa hot tub performance but it also prolongs the operational life of the heater, the pumps and the control system.

FAQ

Q1: What is 84°F in Celsius? Is it comfortable for taking a bath in the jacuzzi outdoor spa hot tub?

84°F equals 28.9°C approximately so this is about 2°C lower than the temperature of the water used for constant-temperature swimming pools and hence not really comfortable for bathing in the outdoor whirlpool spa hot tub.

Q2: If the outdoor whirlpool spa hot tub stops at 84F degree that would probably mean the heater was broken?

It's possible but other possibilities exist as well which include a blocked filter, poor flow of water, wrong operating mode, a wrongly wired power supply, a dead temperature sensor, and maybe some safety measure that has been engaged. Hence, it's suggested that instead of just going by the first assumption you troubleshoot the problem further if you like.

Q3: Shouldn't we expect slower heating when our outdoor hot tub is located outdoors in cold weather?

Outdoor hot tubs do take more time to reach the desired temperature in cold climates and if the thermal cover is loose or even missing, the heat loss dramatically increases which further prolongs the heating time.

Q4: How often should you clean the jacuzzi outdoor spa hot tub filter?

Cleaning and replacing the filter of an outdoor whirlpool spa hot tub are important tasks for regular maintenance. As a rule of thumb residential users can clean the filter every two to four weeks and get a replacement for it either as an annual job or when needed, which depends on the outdoor whirlpool spa hot tub model. This is essential for the maintenance of proper water flow for circulation and avoidance of heating system inefficiency due to low level of water flow.

Q5: How should I tell if it is a malfunction of the control system or just a settings problem?

If you find after having looked up set temperature, operating mode, water level, filter, and power supply the outdoor whirlpool spa hot tub still only keeping up a 84°F without any change for a long period of time or it is accompanied or preceded by such symptoms as errors of code, warnings in a strange sound, or heater failure, you may as best contact professional service persons to test control boards, sensors, and other ‍‌‍‍‌equipment.