BoilerFaultCodesPotterton B.(1) Fault Code
Also written as B1 — same fault.
The Potterton B.(1) fault code means: your boiler is failing to stay lit after you try to start it because the pilot light is going out as soon as you let go of the ignition button.. It appears on 3 Potterton models in our database.
Technical description: Main burner fails to light and pilot is extinguished when pressure on the control knob is released - Control knob not held down long enough.
What causes the Potterton B.(1) fault?
This fault occurs when the safety system, centered around a part called a thermocouple, fails to detect a stable flame. When you release the ignition button, the boiler shuts off gas flow because it incorrectly believes the pilot light has gone out, or the components responsible for holding the gas valve open have physically worn out. The most common reason is a deteriorated thermocouple tip that can no longer generate the tiny electrical pulse needed to keep the boiler running.
This issue is frequently seen during the first cold spell of autumn when the boiler is switched back on after being idle throughout the summer.
DIY fix possible
Locate the gas control knob on the boiler.Follow the lighting instructions on the boiler casing, ensuring you press the control knob in fully.Hold the control knob down for at least 20 to 30 seconds after the pilot flame appears before slowly releasing it.
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Gas Safe Register →Potterton models that show the B.(1) fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton B.(1) fault code information on this page is sourced and cross-checked against the official Potterton service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026