Error D1 240

Safety first: Do not attempt any internal electrical or gas repairs unless you are a qualified Gas Safe engineer. Before touching the boiler, switch the boiler to the off/standby position and isolate electrical power at the fused spur or consumer unit if you are going to visually inspect external connectors. Do not isolate the gas supply unless instructed by a Gas Safe engineer. Keep any children or pets away while you work. If the boiler is under warranty, contact Worcester Bosch or your installer before opening or removing internal panels.

Initial checks a homeowner can do:

1) Record the exact error code and take a photo of the display and any flashing lights. Note any symptoms (no hot water, no heating, frequent lockouts).

2) Try a simple reset: press and hold the reset or ✓ button for about 8 seconds until the boiler reboots. If the fault clears and stays cleared, monitor the boiler for recurrence. Repeated resets only hide an underlying issue.

3) Check the system pressure gauge. The gauge should be around 1.0 bar with the system cold; when the boiler runs it will typically rise. Top up the system only if pressure is low and you know how to do so (use your filling loop or internal key if fitted). Low pressure can cause other faults but is not usually the direct cause of a sensor short.

4) Look for signs of leakage or condensation around the boiler, the pressure relief discharge pipe, radiator valves and visible pipework. Note any wet patches, drips or corrosion.

Specific diagnostic and basic remedial steps you can safely try:

1) If you can access the area around the boiler without removing sealed panels, look for the return sensor connector or wiring loom entry point and check for obvious signs of water, corrosion, loose connectors or damaged wires. Only perform a visual inspection; do not unplug internal connectors if you are not competent. If you can unplug an easily accessible external connector (and the boiler is powered off), check it for corrosion, dry it and refit it firmly.

2) If the boiler or pipework near the sensor is wet (condensate or leak), dry the area thoroughly with a cloth and allow time to dry. After drying, restore power and reset the boiler. A temporarily wet sensor/connector can sometimes clear the fault, but this may be a sign of an underlying leak that needs attending.

3) If the fault readout specifically states short circuit or the code returns immediately after reset, do not continue to power cycle. This indicates an electrical short or failed sensor which requires professional testing.

4) If you have a readable manual or quick-info function on the boiler, follow any manufacturer guidance given for D1 or return sensor faults and make a note of any additional codes reported alongside D1 240.

When to call a professional and what to tell them:

- Call a Gas Safe qualified heating engineer or Worcester Bosch service if the code persists after reset and drying, if you see damaged wiring, if the boiler remains in lockout, or if you are uncomfortable performing the visual checks. Do not attempt to bypass or short out sensors.

- When you call, report: the exact fault code (D1 240), whether the fault is persistent or intermittent, what happened when you reset the boiler, the system pressure reading, any visible leaks or wet connectors, any recent power cuts or freeze events, and whether the boiler is still under warranty. Send the photo you took of the display and any wet/damaged areas.

What the engineer will do (for your information):

- Isolate and safely open the boiler, check the return NTC sensor, wiring loom and plug for short/open circuits, measure sensor resistance and continuity, and check the control board inputs. They will replace the sensor and/or repair wiring or the connector if required, and test the system for leaks or condensation sources if water ingress is found.

Final notes: A temporary dry-and-reset may restore operation, but it does not guarantee a permanent fix. Return sensor faults can be caused by component failure, wiring problems or water ingress; accurate diagnosis and safe repair usually require a qualified engineer. If the boiler is under warranty, contact Worcester or your installer before doing anything that might affect cover.