1-d1 Low

Worcester Bosch 1-d1 Fault Code

Also written as 1D1 — same fault.

The Worcester Bosch 1-d1 fault code means: your boiler is reporting an issue with the solar panel temperature sensor, which usually means the system is detecting an unusual reading from your solar thermal panels.. 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: Collector temperature: Is only displayed, if a solar module is connected.

What causes the Worcester Bosch 1-d1 fault?

This fault occurs when the boiler's control system loses communication with the sensor that monitors the temperature of your solar panels. The most common reason is a broken or corroded wire between the roof and the boiler, or a sensor that has failed due to extreme weather exposure. Because the boiler cannot tell how hot the panels are, it stops integrating solar heat into your hot water system for safety.

This fault is more common in summer, as high thermal stress from peak sunshine can cause aging sensors or damaged wiring to fail under extreme heat.

Typical repair cost £90-180 (including labour)

Engineer required

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

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Worcester Bosch models that show the 1-d1 fault code

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

Source

Worcester Bosch 1-d1 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