BoilerFaultCodesGlow-worm F19 Fault Code
The Glow-worm F19 fault code means: your boiler has detected that a temperature sensor is disconnected or has failed, which is currently preventing the heating from starting to protect the system from freezing.. It appears on 3 Glow-worm models in our database.
Technical description: Central Heating flow thermistor disconnected (frost protection).
What causes the Glow-worm F19 fault?
This fault occurs when the boiler's control board loses communication with the temperature sensor on the main heating pipe. The most common reason is that the sensor has developed an internal electrical failure or the wiring connecting it to the brain of the boiler has become loose or damaged.
This fault is frequently triggered during the first cold snap of autumn when the system's frost protection kicks in and attempts to read a sensor that has degraded over the summer.
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 →Glow-worm models that show the F19 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F19 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026