1-d2 Low

Worcester Bosch 1-d2 Fault Code

Also written as 1D2 — same fault.

The Worcester Bosch 1-d2 fault code means: your boiler is reporting a minor sensor issue related to your solar hot water system, but it is not a breakdown of the central heating itself.. It appears on 1 Worcester Bosch model in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Cylinder temperature bottom: Is only displayed, if a solar module is connected.

What causes the Worcester Bosch 1-d2 fault?

This fault occurs when the boiler loses communication with the sensor located at the bottom of your solar hot water cylinder. The most common reason is a faulty temperature sensor (NTC) or a break in the wiring connecting the solar control module to the tank. While your central heating will continue to work, the system can no longer monitor how much free heat is being provided by your solar panels.

Typical repair cost £90-180 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Worcester Bosch models that show the 1-d2 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Worcester Bosch 1-d2 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026