36 Inch M7 Sensor 91047 Viking Spas

Viking Spa Sensor: 36 Inch Sensor with 1/4 Inch Bulb for Balboa M7, LE and Value System.

Each system for the M7 Balboa spa heater uses two sensors. One for high limit and one for temperature. Both sensors are identical and interchangeable and mount to the M7 heater.

Manufacturer Recommends Replacement of Both Sensors since they interact with the electronics and each other as a pair.

This Balboa factory original part includes:

• M7 Hi Limit/Temperature Dual Duty Sensor Probe 1/4" with 2" long Bulb
• M7 Sensor Mounting Cap
• Sensor Bulb O-ring with Washer
• 1/4" Sensor Diameter
• 2 Pin Connector - 2 Wire Cable
• 36" Long Cable

We also offer the threaded sensor mount that fits into the heater, but usually you can use the one that is there.

The cable length for this M7 temperature / hi limit sensor is 36 inches.  There is a black connector and the cable has 2 pins.

Note the 2 sensors in the heater are the same, so this is a dual purpose sensor that will replace either one.

If there is a sensor issue, the manufacturer recommends replacing them both at the same time.

How do the sensors work?

The two sensors located within the Balboa heater housing compare the inlet water temperature with the outlet water temperature, regardless of the direction of water flow.

This allows for determining the presence of water, low flow, temperature limit, and operating temperature.

The system will automatically select the sensor that is exposed to the lowest temperature as the spa water temp controlling sensor. The sensors work together with on-board software that allows the spa to be controlled without the use of external pressure switches, flow switches, or external temperature sensors.

Troubleshooting Balboa M7 Temperature Sensors (for techs)

All electrical work on spas should be performed by qualified service technicians or electricians.

Power off spa (unless you are an electrician that is qualified to work on live circuits, then it's your call - the downside is you may get electrocuted or die).

Check that the sensor wires are not cracked and that they have not been chewed through by a possum or rodent.

Be sure the sensors are snuggly connected to the circuit board and that the terminals/plugs are clean.

The next section will require power to the spa - that means no hands near any wiring, circuit board or other shock/electricution hazard. Of course since these directions are only for qualified service personell, we don't have to tell you that.

If the sensors are not completely failing, but show a 2 degree or larger difference between the 2 sensors when not heating (which can cause control panel sensor error messages), then determine which sensor is always reading higher (A vs B or temp vs. hi-limit).  Unplug the 2 sensors from the board and switch them out plugging each one into the socket for the other one. 

If a stray fault occurs (gibberish on the panel), just press any panel button to clear. 

Within a minute or so (but not over 2 minutes, 'cause then heating may start), according to the Balboa technical manual for technicians only, see if the same sensor is reading consistently higher than the other one. 

If the same sensor is reading higher after sensor interchange, chances are the problem is on the circuit board which would call for a circuit board replacement.  See our circuit boards if you need a new one or email us with your circuit board part number or chip/revision number as found on the circuit board.  If you need more information on sourcing a replacement board, see our article on how to replace a circuit board.

If the opposite sensor is now reading higher, then the problem is with the sensor set, so replace BOTH sensors.

This next test will require a spare M7 sensor set for testing - so since you are a tech, you would have those on the truck.

If there is an error message about a faulty or open sensor, unplug the sensor set (but leave the original sensors in the heater) and plug in the test sensor set. Put both sensors in the same cup of warm water (ideally hotter than the spa water/set temperature so spa does not try to heat) -and verify they read within 1 degree F of the same temperature.  If the problem is solved, replace the sensors, if not then do more test and don't replace the sensors.  Try re-plugging in the original sensors in case there was a connection problem.  Otherwise, it might be circuit board time....

There is also a method of doing an ohm test with sensors completely unplugged, but for that, refer to the Balboa M7 service manual.

The above is intended to be an informational overview of how a tech would approach troubleshooting a Balboa M7 temperature sensor issue and is not meant for the homeowner to do their own repairs.

Get circuit boards and replacement temperature sensors right here at Hot Tub Outpost.