SN1 and SN3:
a sensor has failed.

What these codes mean

Sensor codes are the most straightforward thing a hot tub control pack ever tells you. It is not guessing at a symptom — it is reporting that a specific component has failed electrically.

• SN1 / SNA — temperature sensor. The main sensor is open or shorted. The board no longer knows the water temperature, so it disables the heater.
• SN3 / SNB — high-limit sensor. The safety sensor at the heater has failed. Heating is disabled deliberately, because running a heater with no working safety cut-out is not something any pack will allow.

In both cases the tub is behaving correctly. Nothing is on fire, nothing is leaking, and the water is fine. What has gone is the ability to measure it.

There is not much to check first

Unlike FLO or DR , this is not a code with a homeowner checklist attached. There is no filter to pull or valve to open that will bring a failed sensor back. Two things are worth doing:

• Power cycle it once. Occasionally a code is latched rather than live. Once.
• Note whether it is SN1 or SN3. It tells the technician which part to bring, and that is the difference between one visit and two.

Why we do not just swap the part blind

A sensor code names the component but not the cause. Sensors fail on their own, and they also fail because water has got somewhere it should not, because a connector has corroded, or because the harness has chafed. Replacing the sensor without checking what killed it is how the same code comes back in three months.

The $185 service call covers the trip and the diagnosis, you hear the fault and the price before anything is replaced, and we carry the majority of common parts. Dr. Spa has serviced all makes and models since 2001, which matters here because sensor part numbers are pack-specific and plenty of those packs are older than the shops that sold them.

Where we stop

Electrical work on a spa circuit is licensed work in Michigan and Dr. Spa does not do it. Sensors, heaters, pumps and the pack are all on the spa side of the disconnect and are ours. The circuit feeding the tub is not, and if that is where the fault is, we will tell you exactly what to ask a licensed electrician for.

Related codes

A failing sensor often shows up first as an OH overheat or a tub that will not hold temperature before it fails outright. The full error code index covers all twelve.