Error 2966 B

Safety precautions:

1) If you smell gas, leave the property immediately, call the gas emergency number and do not operate the boiler. If you suspect carbon monoxide (unusual smells, black soot, headaches), turn the appliance off, ventilate the room, and call a Gas Safe engineer or emergency services.

2) Before inspecting the boiler, switch off the electrical supply to the boiler at the isolator and allow the unit to cool. Do not remove the boiler cover or attempt internal electrical repairs unless you are a qualified engineer.

Initial homeowner checks you can try (non-invasive):

1) Note whether the error happened during a particular activity (initial heat-up, after radiator bleeding, after servicing). Take a photo of the display and exact code and any flashing pattern.

2) Reset the boiler once: on many Worcester models press and hold the reset button for 3 seconds, or use the reset position on the temperature dial for 3 seconds, then return to normal. Observe whether the error returns and how quickly.

3) Check system pressure on the boiler gauge. If pressure is very low (<0.7 bar) repressurise to the recommended level (typically ~1–1.5 bar) using the filling loop per the manual, then reset and observe. Low pressure can affect circulation.

4) Listen for the central heating pump when the boiler calls for heat. You should hear or feel the pump running (a quiet hum). If the pump is completely silent when the boiler is calling, do not attempt internal repairs — call an engineer.

5) Check radiators and TRVs: ensure lockshield valves and TRVs are open and that a large number of radiators are not closed, which can reduce flow through the heat exchanger.

6) If you recently bled radiators, bleed any trapped air fully and then top up system pressure. Airlocks can prevent proper flow and cause rapid temperature rises.

Diagnostic steps you can perform without opening the boiler:

1) After a reset, run the heating and carefully feel (or use an infrared thermometer) the flow and return pipes near the boiler (outside the casing). If the flow pipe gets hot very quickly while the return stays much colder (large delta T), that supports a circulation restriction. Be careful — pipes may be very hot.

2) Check for external isolation valves on the boiler flow/return being fully open. Also check the actuator or zone valves (if fitted) are calling for heat and not stuck closed.

3) Ensure the flue terminal is clear of debris — poor combustion or flue issues can sometimes be reported as related temperature sensor faults. Do not remove or inspect the flue internally.

4) If the error is intermittent and the boiler runs briefly then trips, record how long it runs before tripping and whether it happens on both heating and hot water.

When to call a professional (required in these situations):

1) The fault repeats after simple resets and the above non-invasive checks.

2) You suspect a failing pump (no sound or very noisy), blocked heat exchanger, or scale buildup in a hard-water area.

3) The flow or safety temperature sensors or their connectors are suspected faulty (open/short), wiring looks damaged, or you cannot locate the cause of rapid temperature rise.

4) Any time you are asked to open the boiler casing, touch internal components, or replace sensors, the pump, or control board — these are gas-qualified tasks and must be done by a Gas Safe registered engineer.

What a Gas Safe engineer will check/likely do (for your information):

1) Run the boiler in diagnostic mode and read logged sensor values and exact gradient thresholds. Capture error history.

2) Measure flow and return temperatures with proper instruments and check the delta-T and ramp rate against spec.

3) Inspect and test the flow NTC sensor and safety temperature sensor and their wiring/connectors. Replace faulty sensors and re-test.

4) Check pump operation, impeller condition and speed settings; free or replace a seized or failing pump.

5) Inspect for system blockages, closed valves, stuck zone valves, or airlocks; carry out powerflush or chemical descaling if heat exchanger blockage or scale is present.

6) Examine the control PCB if repeated sensor faults or erratic behaviour suggest an electrical control issue.

Notes and practical advice:

1) Record the error code (2966 B), the conditions when it happened, and how frequently it occurs — this helps the engineer diagnose faster.

2) Avoid repeated resets more than a couple of times — repeated lockouts can indicate a serious fault and waste time before the engineer visit.

3) Keep evidence of recent work (radiator bleeding, system fills, new parts) to tell the engineer; recent changes often explain sudden gradient faults.

4) If you are in any doubt about safety or are unable to restore normal operation with the simple checks above, arrange a Gas Safe registered engineer to inspect and repair the boiler.