Error 2964 B

Safety precautions:

- Do not attempt internal repairs on the boiler unless you are a qualified, Gas Safe registered engineer. Working on gas appliances is dangerous.

- Before touching any electrical parts, isolate the boiler at the mains and switch off the gas if instructed by a qualified engineer.

- Wear gloves and eye protection when bleeding radiators or handling water. Have a cloth and container ready for any spilt water.

Initial homeowner checks (safe, do these first):

1) Note the fault code, the time it occurred and any other behaviour (noises, loss of water pressure, recent radiator work). This information will help an engineer.

2) Check the system pressure gauge on the boiler. It should typically be around 1.0–1.5 bar when cold. If pressure is low (well below 1 bar) repressurise using the filling loop according to the boiler manual and then re-test. If you are not sure how to do this, stop and call an engineer.

3) Check that the boiler isolation valves (flow and return service valves) and any external isolation valves are fully open. These are often lever-type or slotted screw valves near the boiler—open to be parallel with the pipe or aligned with the flow direction. Do not force valves you are unsure about.

4) Turn the heating on and feel the flow and return pipes from the boiler after a few minutes (carefully—they may be hot). The flow pipe should be noticeably hotter than the return. If both are the same temperature the pump may not be circulating.

5) Bleed radiators to remove trapped air. Airlocks reduce circulation and are a common cause. After bleeding, check system pressure and top up if necessary.

6) Listen for the pump running (a faint hum or vibration) with the boiler powered and calling for heat. If you hear nothing at all the pump may not be powered or may have failed.

Diagnostic steps and next actions (homeowner and what to tell the engineer):

7) If the boiler has a simple reset button and the manual permits, you may try one reset to clear a transient fault. If the fault returns immediately do not keep resetting; this can mask a real problem.

8) If you can access the pump isolator valves and are confident, you can check they are open. If you are experienced and only after isolating power, some pumps can be freed by gently rotating the motor shaft by hand (small rotary movement) to free a seized impeller—but only do this if you are competent. If in doubt, stop and call an engineer.

9) If after bleeding radiators, topping up pressure and ensuring valves are open the fault remains, the likely causes are: seized/failed pump, blocked or scaled heat exchanger, blocked pipework or a faulty flow/temperature sensor or its wiring. These require an engineer to diagnose and repair safely.

10) Make a note of any other error codes, unusual smells (gas), leaks, or noises. If you detect a gas smell, leave the property immediately and call the gas emergency number.

When to call a professional and what they will do:

- Call a Gas Safe registered Worcester Bosch competent engineer if the basic checks above do not clear the fault, or if you are not comfortable carrying them out.

- The engineer will perform a controlled diagnostic: check pump electrical supply and operation, test the flow sensor and NTC wiring, measure flow/return temperatures, inspect and possibly chemically flush the system or clean/replace the heat exchanger if blocked, and replace the pump or sensor if faulty. They will also check control board inputs and any software/service mode diagnostics.

Final notes:

- Do not attempt gas or sealed-system repairs yourself. Components such as the pump, heat exchanger, sensors and wiring should be handled by a registered engineer.

- If the boiler is locking out and you have no heating or hot water, arrange an engineer promptly—continuing to try to run a boiler with suspected circulation failure risks damage. Provide the engineer with the fault code (2964 B) and the steps you have already taken to speed diagnosis.