Error 1074 W

Safety precautions:

1) If the boiler is in a protected or enclosed cupboard ensure good ventilation and do not block openings. 2) Before touching anything, turn the boiler off at the electrical isolation switch or fused spur and, where present, switch off any external room thermostats or controls. 3) Do not attempt gas work, soldering, or mains electrical repairs yourself. If you are not confident working with electrics, stop and call a Gas Safe registered engineer.

Initial homeowner checks (safe, no internal access required):

1) Note the exact error: record "1074 W" and any additional cause code from the boiler information menu (press the spanner/return button to view cause codes). Take a photo of the display. 2) Try a simple reset: press and hold the boiler reset button (or follow the manual’s reset method) for 3 seconds. Wait a minute and see if the code clears and the boiler re-lights. 3) Check the mains electrical supply and fused spur to the boiler—ensure it hasn’t tripped. 4) Check system water pressure on the gauge; if very low (under ~1 bar) top up to the recommended pressure and retry a reset. 5) Look for obvious signs: wetness, condensation, corrosion or loose external pipework or sensor leads that are visible without removing covers.

If the fault persists — diagnostic steps for someone with basic DIY electrical skills and a multimeter (only attempt if you are competent and appliance is isolated):

1) Isolate electrical power to the boiler at the fused spur. Confirm power is off. 2) If you are comfortable removing the outer case and the boiler is out of warranty, remove the front cover to access the sensor connections. If you are unsure, stop and call an engineer. 3) Locate the central heating flow temperature sensor and its connector. On most Greenstar models it is a small NTC fitted into the flow pipe or into a pocket; the wiring will lead to a small plug/connector to the PCB or wiring loom. 4) Visually inspect the connector and wiring for damaged insulation, loose pins, corrosion or water ingress. Re-seat any unplugged connectors firmly and ensure they clip home. 5) With the boiler still isolated, measure the sensor resistance across the two sensor pins using a multimeter set to ohms. For NTC sensors you should read a finite resistance (not infinite/open circuit). Values are model-dependent but a typical flow NTC is in the kiloohm range at room temperature (for many boilers around 10 kΩ at ~25°C) and resistance should fall if the sensor is warmed. An infinite reading or very high open-circuit indicates a failed/open sensor; a near-zero short indicates a shorted sensor or wiring short. 6) If wiring or plug faults are found, you can carefully clean corroded pins and reseat; ensure everything is dry before re-powering.

Repair and replacement steps (recommended to be carried out by a Gas Safe engineer):

1) If the sensor is confirmed faulty (open or short) or the connector/wiring is damaged, replace the flow temperature sensor and/or repair the wiring harness. 2) After replacement, the engineer will clear fault codes and run the boiler to confirm correct temperature readings and stable operation. 3) If sensor replacement does not cure the problem, the technician will inspect the PCB/wiring to the control box for faults; the PCB or heat control module can occasionally be the cause and requires specialist repair/replacement.

When to call a professional and what to tell them:

1) Call a Gas Safe registered engineer if the basic reset and external checks do not clear the fault, if you find internal wiring damage, if you cannot access the connector safely, or if you are not confident with electrical measurements. 2) When you call, provide model (Worcester Bosch Greenstar 8000), the exact fault code (1074 W) and any cause code from the information menu, describe what checks you have already done (reset, pressure, visible connector inspection), and share photos if possible.

Additional notes:

1) Do not continue to use the boiler if it is behaving erratically or showing overheating signs. 2) Keep documentation, photos and notes of any steps you took — this helps the engineer. 3) Because this fault involves temperature sensing and the boiler’s safety functions, replacement and final testing should always be performed or certified by a qualified Gas Safe engineer.