Error 2963 B

Safety precautions:

1. If you smell gas, evacuate the property and call the gas emergency services immediately. Do not try to investigate the boiler.

2. Turn off the boiler at the front control panel and at the electrical isolator or fused spur before removing any covers. If you are not confident working near electrical equipment, stop and call a Gas Safe engineer.

3. Do not attempt to work on gas valves, the burner or any gas-carrying components unless you are Gas Safe qualified. Internal electrical and temperature-sensor work should also be done by a competent person or engineer.

Initial checks a homeowner can do (no tools or minimal tools):

1. Note down the exact error code and any other codes or flashing lights. Do not repeatedly press reset; one attempt to reset or power-cycle is acceptable to see if the fault was transient.

2. Check the boiler display/message log for additional codes that might indicate a related fault.

3. Check the system water pressure on the pressure gauge. If the pressure is very low (below recommended operating pressure, typically around 1–1.5 bar), top up the system following the boiler manual. Some sensor/flow-related faults can appear in systems with circulation problems, but 2963 is primarily a sensor signal fault.

4. Check any external controls (room thermostat, programmer, wireless controls) are powered and connected correctly. Disconnecting external controls can sometimes change behaviour; confirm they are not causing a communication fault.

If you are comfortable performing a basic visual inspection (and only after isolating electrical supply):

1. Turn off and isolate the boiler electrically. Wait for the appliance to cool.

2. Remove the boiler front cover per the user manual. Look for obvious signs: disconnected plugs, corroded or damaged wires, burnt connectors, or water ingress near wiring looms and sensor plugs.

3. Locate the flow temperature sensor and the heat-exchanger sensor connectors (consult the boiler wiring diagram or manual if you have it). On many Greenstar models these are NTC sensors mounted on or near the flow pipe/heat exchanger with a small plug into the pcb or wiring harness.

4. Check the sensor plugs are fully seated and the retaining clips are in place. Gently unplug and re-plug the connector to reseat it. Inspect the pins for corrosion or bending.

If you have a multimeter and feel confident using it (only with power isolated):

1. With the connector unplugged, measure the sensor resistance across the two sensor wires. NTC sensors change resistance with temperature: an open circuit (very high/infinite resistance) suggests a broken wire or failed sensor; a short (near 0 ohms) suggests a shorted sensor or wiring fault. A resistance that changes noticeably when you warm the sensor (with your hand) indicates the sensor is responsive. Exact resistance values vary by sensor type—if you have the datasheet use that; if not, the key checks are open-circuit or short-circuit.

2. Check continuity of the wiring from the sensor plug back to the PCB connector if possible. A broken conductor will show as an open circuit.

If you find a loose connector, simple corrosion or a damaged wire that you are confident to repair safely, reseat or replace the connector/wire as an interim measure. After reassembly, restore power and test the boiler. If the fault clears and does not return, book a service/engineer visit to confirm the repair.

When to call a professional (recommended actions and what they will do):

1. If reseating connectors or topping up pressure does not clear the code, or if you find an open or shorted sensor, arrange a Gas Safe registered engineer. They will perform safe live diagnostics, confirm sensor resistance against specification, replace the faulty NTC sensor(s) and any damaged wiring, and test the control board and system operation.

2. If the wiring and sensors test OK but the fault persists, the control board or burner control unit may be at fault — this requires professional diagnosis and likely parts replacement.

3. If the fault occurs intermittently or after work on the boiler, do not keep resetting the appliance repeatedly. Let the engineer trace the intermittent wiring or connector fault.

Final notes:

1. Error 2963 B commonly ends up being a loose/disconnected sensor plug or a failed flow/heat-exchanger temperature sensor, both of which are routine for a qualified engineer to fix. However, because the work requires access inside the boiler and may involve electrical and gas-related systems, repair should normally be completed by a Gas Safe registered engineer.

2. Provide the engineer with the exact fault code, any steps you’ve taken, and whether the code cleared temporarily after a reset — this helps them diagnose faster on arrival.