BoilerFaultCodesWorcester Bosch 1-d3 Fault Code
Also written as 1D3 — same fault.
The Worcester Bosch 1-d3 fault code means: your boiler is reporting an issue with the pump that circulates fluid between your solar panels and the water tank.. It appears on 3 Worcester Bosch models in our database.
Technical description: Collector pump: Is only displayed, if a solar module is connected.
What causes the Worcester Bosch 1-d3 fault?
This fault occurs when the system detects that the pump responsible for moving heated fluid from your solar panels to your hot water tank is not functioning correctly. The most common reasons are a mechanical failure within the solar pump itself, a faulty sensor failing to read the fluid temperature, or a communication error between the solar control module and the boiler.
This fault is more common during the summer months when high levels of solar radiation put the pump and sensors under maximum operating demand.
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-d3 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 1-d3 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