BoilerFaultCodesWorcester Bosch 203 Fault Code
The Worcester Bosch 203 fault code means: your boiler is working correctly and is simply waiting for a signal from your thermostat or timer to start heating.. It appears on 16 Worcester Bosch models in our database.
Technical description: Boiler in standby, no heat energy demand
What causes the Worcester Bosch 203 fault?
This code appears when the boiler has reached its required temperature or has fulfilled its current task and is now sitting in a 'ready' state. It is physically waiting for your thermostat to detect a drop in room temperature or for a timed schedule to trigger a new request for heat. Essentially, the system is resting because it believes every part of your home is currently warm enough.
This status is more frequently observed during spring and autumn when the weather is mild and the thermostat reaches its target temperature quickly.
DIY fix possible
Check that your room thermostat is turned up higher than the current room temperature.Ensure your heating programmer or app is set to an 'On' period.Check if your wireless thermostat has run out of batteries.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like 203: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Worcester Bosch models that show the 203 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 203 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.
- Worcester Bosch 24/28/35 CDi MkII manual (PDF)
- Worcester Bosch Greenstar 1000 manual (PDF)
- Worcester Bosch Greenstar 12i System manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026