Balboa Hot Tub SnA Error — High Limit Sensor Fault

What Does This Error Mean?

SnA means the high-limit (safety) temperature sensor — sensor A — has failed or is reading out of range.
The control pack disables heating because it can't safely monitor for overheat.
This is usually a sensor failure (50–100 USD part) and a service-tech repair on most installations.
The spa won't heat until SnA is cleared.

Affected Models

Balboa BP series control packs
Balboa GS series
Balboa GL series
Balboa M7 spa packs

Common Causes

High limit sensor failed (open or shorted)
Sensor wire disconnected at the controller
Sensor wire damaged where it routes through the cabinet
Connector loose at the controller
Controller sensor input damaged

How to Fix It

Power off at the breaker.

Switch the spa's breaker off.
Wait 60 seconds.
Don't try to work on sensors with the controller live.
Locate the high limit sensor.

The high limit sensor is on the heater housing — typically a thin probe inserted into a port on the heater body.
Two wires run from the sensor to the control pack.
Note the orientation before disconnecting.
Inspect the sensor and wires.

Look at the sensor itself for visible damage — burned spots, corrosion, melted insulation.
Check the wires for chafe damage or cuts where they route through the cabinet.
Check the connector at the controller for any green or white powder (corrosion).
Test continuity (advanced).

If you have a multimeter, test sensor resistance at room temperature — should be around 10K ohms (specific value varies by sensor model, see Balboa documentation).
Open or shorted readings confirm sensor failure.
This is informational — replacement is the same regardless.
Replace the sensor.

Balboa high limit sensors are 50–100 USD parts at spa supply stores.
Match the model number for your specific control pack (BP-2100, BP-501, etc.).
Replacement is usually a 30-minute job with a wrench — sometimes the heater needs partial draining.
Hire a spa tech if you're not comfortable.

Frequently Asked Questions

What's the difference between SnA and SnB?

SnA is the high limit (safety) sensor — monitors for overheat shutdown.
SnB is the regulating sensor — monitors actual water temperature for heater control.
Different sensors, different roles, but similar replacement procedure.
Both are needed for safe operation.

Can SnA come back after a sensor change?

If wiring or controller is also damaged, yes.
If the new sensor reads correctly but the controller's sensor input is failed, you'll see SnA return.
If that happens, the control pack itself needs replacement (300–700 USD) — significant repair.
For older spas, weigh repair against new control pack pricing.