Error 1073 W

Safety precautions:

- If you are not competent with electrical or plumbing work, stop and call a Gas Safe registered engineer.

- Before touching anything, isolate electrical power to the boiler at the mains and switch the room thermostat and programmer to OFF. Do not attempt internal checks with the boiler powered.

- Do not work on gas valves, burners or internal gas components—only a Gas Safe engineer should do that.

- If you need to drain any water to access a sensor, be aware of hot water and potential scalding; isolate the boiler and let it cool first.

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

1. Reset the boiler: press and hold the reset button (or follow the model reset procedure) for 3 seconds. If the error clears and stays clear, monitor the system. If it returns, further checks are needed.

2. Check the boiler display for any additional cause codes in the information menu (press the spanner/return button if available) and write them down for the engineer.

3. Check system pressure on the boiler gauge. Very low pressure can cause odd behaviour, though a 1073 specifically points to the flow sensor.

4. Look for obvious signs of water leaks, corrosion or damp around the boiler and wiring looms—moisture can cause short circuits.

5. If you can safely access the boiler front cover, with the power isolated you may visually inspect the wiring harness and connectors for the flow sensor for loose plugs, squashed wires, or visible damage. Do not disconnect or probe connectors while power is connected.

Specific diagnostic and repair steps (for a competent person or engineer):

1. Power down the boiler at the isolation switch and at the mains. Confirm it is safe to work on.

2. Locate the CH flow temperature sensor (usually clipped into the flow pipe or mounted on the primary flow within the boiler hydraulic block). Identify the connector that links it to the control board.

3. Inspect the connector and wiring for corrosion, burn marks, chafing or water ingress. Reseat the connector (disconnect and reconnect) and ensure a secure fit.

4. With power still off, use a multimeter to check the sensor wiring for short to earth or to other conductors. A short-circuit fault will typically show a very low resistance (near 0 Ω) between the sensor wires or between a sensor wire and earth. A healthy NTC sensor will show a finite resistance value; many Worcester NTC flow sensors are around 10 kΩ at 25 °C (check the boiler’s service data or leave measurement to the engineer). Do not guess values—record readings for the engineer.

5. If the sensor wiring appears intact but the meter shows a short, replace the flow sensor. Replacement involves isolating and draining part of the heating circuit, removing the old sensor, fitting the new sensor and then refilling and bleeding the system and checking pressure. This is normally done by a Gas Safe engineer.

6. If the sensor tests OK but the error persists, the fault may be with the wiring harness inside the boiler or the control PCB. An engineer should inspect and test the PCB, connectors and the related safety sensor(s). Do not attempt PCB repair yourself.

When to call a professional:

- If the error returns after a reset or you find evidence of damaged wiring, water ingress or if the multimeter indicates a short, call a Gas Safe registered engineer.

- Any work that involves draining the heating system, replacing sensors, opening the boiler case, or testing/repairing the PCB should be done by a qualified engineer.

What the engineer will typically do:

- Confirm the fault using the boiler’s error and cause codes, test the sensor and wiring with accurate instruments, isolate and replace the faulty flow sensor if required, inspect and repair any damaged wiring or connectors, and if necessary test or replace the control PCB. They will also refill, purge and pressure-test the heating system after any work that opens the water circuit.

Notes and final tips:

- Record the exact error code (1073 W) and any three-digit cause code shown in the information menu—this helps the engineer diagnose faster.

- Avoid repeated resets; if the boiler locks out repeatedly, isolate and contact an engineer. Repeated attempts to run the boiler with an electrical fault could cause further damage.

- Keep your boiler manual and service records available for the engineer. Contact a Gas Safe registered Worcester Bosch service engineer to ensure the repair is carried out safely and in line with manufacturer guidance.