Boiler display shows 'Comm Error', 'Sensor Bus Error', or similar; multiple sensor readings may be lost.

Safety first: Turn off power before unplugging or plugging any control harnesses.

• 1. Reseat connectors: Open the control compartment and gently unplug then replug the low-voltage harnesses between the main control and any expansion or sensor modules.
• 2. Inspect cables: Look for pinched, abraded, or chewed cables, especially in chases or near sharp edges. Replace damaged wiring.
• 3. Reduce electrical noise: Ensure sensor and communication cables are not bundled tightly with high-voltage or pump wiring.
• 4. Power cycle: After reseating connections, restore power and see if the error clears.

If communication errors persist, the control module or expansion board may need replacement by a technician.