BoilerFaultCodesSime 100 B Fault Code
Also written as 100B — same fault.
The Sime 100 B fault code means: your boiler is not detecting the necessary water pressure to operate safely and will not provide heating or hot water until this is corrected.. It appears on 1 Sime model in our database.
Technical description: Format 100 B
DIY fix possible
Locate the external filling loop, usually found underneath the boilerOpen the filling valve slowly to allow water into the systemWatch the pressure gauge and stop when the needle is between 1.0 and 1.5 barEnsure the filling valve is fully closed and tight
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 100 B: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Sime models that show the 100 B fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Sime 100 B fault code information on this page is sourced and cross-checked against the official Sime service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026