How to Troubleshoot The Sauna High-Limit Switch
The high-limit switch is an extremely important part of a sauna heater design.
So most know that a timer and a thermostat are used to control the time and temperature of a sauna heater. When exactly does the high-limit switch get involved?
In a properly installed heater, the high-limit switch should never get involved in controlling a sauna, it only gets involved if the thermostat fails. If the thermostat fails, the high-limit switch will act as a backup to make sure the heater does not start to overheat. A properly designed high-limit switch will require it to be reset after it has been tripped. This means that if the high-limit switch shuts down the heater, the unit will not turn back on until the high-limit switch is reset, which is done by pressing the high limit reset button, located here on the heater unit.
So what would cause the high-limit switch to trip? Is it always because of a failed thermostat?
The actual cause is usually for other reasons. Since 90% of our sauna heaters are installed in a commercial environment, our units are exposed to a lot of sauna bathers all over the world. Most facility operators keep their sauna temperatures between 165-175. For the general population, that is a safe range; however, there is a small and growing percentage of the population that like the sauna temperatures in the 190s. The issue for these people is that sauna maintenance personnel are posting signs that say “do not pour water on the rocks”. The reason operators do not want bathers to pour
water on the rocks is because it passes through the rocks onto the elements and can in some cases spill onto the electrical connections. This significantly shortens the life of the heating elements and creates a constant maintenance challenge. We consider it preposterous to abstain from pouring water on the sauna heater rocks, this would be like drinking a cup of coffee without smelling the aroma. We do not have this problem with
Scandia heaters as we have a solid pan design, allowing for repeated pouring of water on the rocks, giving an instant burst in humidity and giving bathers that instant steam and temp boost. No need to mess with the thermostat sensor here. This design protects the elements and wiring from water and ensures a long heater life. Now, if you take someone who has enjoyed this privilege in the past, and now tell them they can’t, you may have an
issue. Some of these “enthusiasts” have figured out that they can trick the thermostat by pouring water or placing a wet rag on the thermostat sensor bulb. This convinces the thermostat that it is cooler in the room than it truly is, therefore it instructs the heater to bring the temp up. A typical high-limit switch will trigger at 195. Since the high-limit switch sensor is built into the heater, it is not subject to this manipulation and will shut down the
heater when the temperature rises when the thermostat is tricked.
How would a club operator know if the high-limit tripping is resulting from bathers messing with the thermostat?
The best way is to reset the high-limit switch and start the unit up again; then, simply wait and watch for the thermostat to regain control of the temperature in the room. If the thermostat, regulates the room at its highest temp (say 175 degrees) and the high-limit does not trip, then it may have been caused by cold water on the sensor bulb trick. Another thing to watch for is if the high-limit trips at the same time every day or on the same day every week. This could indicate it being a particular bather who knows this trick and keeps doing it.
For club owners, they have to keep their eye on the cause of the tripping. Maybe it is a failed thermostat or maybe it is their guests tricking the thermostat.
But what about home owners, what is a suggestion when the high-limit is tripping and they know that they are not tricking the thermostat?
The first step is always to make sure the thermostat is working. Another common issue is proper airflow to the heater. In commercial installations we have tight control of design parameters and vent locations so we can be confident the room is designed properly and has adequate airflow. However, with home applications we sometimes have less control over the room design and venting. Our heaters work on the basis of convection which
makes them very efficient, however, to function properly they require adequate ventilation. If the home sauna does not have adequate venting, hot air is retained in the heater instead of circulating out and this will convince the hi-limit switch that the room is warmer than it truly is, shutting the unit down prematurely. So if the hi-limit switch begins tripping immediately after initial installation it can be due to poor room ventilation.
There are three big questions we need to ask if we are faced with a tripping high-limit switch on a sauna heater.
- Is the thermostat working correctly?
- For commercial environments, does this tripping condition occur on a regular basis? (Sauna Bather Interference)
- Does the room and heater have adequate air flow?
Are there any other conditions that we should be looking out for?
Other things to look out for, albeit less common are things like an appropriately sized heater. If your sauna room is too large for the suggested heater then we have a situation where the heater runs continuously while trying to heat the larger room. Sauna heaters can maintain a rooms temperature 24/7 but during this time they turn on/off as needed to maintain that temperature. If the heater is getting the wrong power supplied
to it, that could also cause issues and the high limit switch tripping. Another cause is mounting the heater too close to the floor. With Scandia heaters, the unit need to be at least 10″ from the floor to allow adequate airflow.
Great points to follow for heaters:
- Correct size
- Vent for airflow
- Mount properly
When all things are done correctly, in a commercial environment, how can bathers be eliminated from tricking the thermostat?
Unfortunately, putting up a sign that says “Do not pour water on thermostat sensor” does not seem to work. So, there is no “perfect”
way to prevent sauna bathers interference; it is best to try and communicate with your clientele as to proper sauna usage, and to try and detect if it is a singular person or a group of people who are regularly abusing the sauna heater thermostat.
We can also use technology to warn us about over temp situations. Sauna alarms are new IOT devices that allow the owners to set a target temperature for the alarm to activate. So, as I mentioned, a sauna room should have a maximum temperature setting of 175 degrees.
High-limit switches are set at around 195 degrees. Operators can set the alarm to trigger at 190. When the sauna hits that temp an email and text alert will be sent instantly to the staff at which time they can go to the sauna asses the situation in real-time. The sauna alarm can also shut down the sauna system as a fail safe mechanism. Having a thermostat, a high-limit switch, and a sauna alarm gives a sauna owner a triple-layer safety system to prevent a heater from overheating
In summary, good room design, the right heater properly installed and giving the bathers the power to control their own environment without manipulating the controls. Follow these steps and you will have a smooth performing sauna room that satisfies a wide variety of