Heater control sensor versus a separate wall gauge

No, they aren't the same thing. The heater control and a wall thermometer each have a sensor of their own, in their own spot, doing a different job.

What the heater control sensor is for

• It tells the heater what to do. The control reads the sensor and decides when to heat. One maker says a well-placed sensor lets the heater respond to the actual room temperature, rather than to localized hot or cold spots.¹
• It can include overheat protection. One maker lists a temperature sensor with overheating protection in its control system.¹ A spare-part sensor from another maker has resettable overheating protection (max. 150 °C).²
• It sits in a set spot. For one maker, not directly above the heater, but 20 in / 50 cm from its outer edge.¹
• It belongs to a particular system. A spare-part sensor is listed as compatible with that maker's electric heaters and control units.²

What a separate wall gauge is for

• It's for you to read. It has no link to the heater. Nothing switches on or off when its needle moves.
• It sits where you choose, within the maker's advice. The distances are in the mounting page.

How makers describe the gap

Here's how one maker puts it: a wall thermometer usually reads lower than the digital control on the same sauna. Its reasoning is that the control reports the very hottest spot, while the thermometer gives more of an average for the bathing zone.³

That's one maker describing its own controls. Others place the sensor differently.

Which one to believe

Neither is "the real" temperature. Each reports where it sits.

• To run the heater: the control's sensor is what the heater goes by.
• To see conditions near the bench: the wall gauge is closer to that.
• When they disagree: look at positions first. The readings page walks through it.

When the control sensor is the problem

If a control shows a sensor error, one maker lists possible reasons: cables aren't properly connected, a cable is faulty, or the temperature sensor itself is faulty.¹

• Don't move or rewire a control sensor yourself. Wiring on a hard-wired heater is licensed electrical work, not DIY.
• Look in the product manual for the sensor location and the temperature class of the overheat protection, as that maker advises.²
• Use only the sensor the heater's maker names for your model.
• Don't guess at the overheat protection class. If the manual doesn't name it for your model, ask the maker before you buy a spare.
• Keep a note of the model number of your heater and control. It makes any support call quicker.

Plug-in controls follow the maker's manual too. If you're unsure, call the maker or a licensed electrician.