BoilerFaultCodesIdeal 9.1.5 Fault Code
Also written as 915 — same fault.
The Ideal 9.1.5 fault code means: your system has a faulty temperature sensor in the main pipework, which means it cannot accurately monitor the water heat flowing through your home.. It appears on 1 Ideal model in our database.
Technical description: Header Thermistor (T1) Error – for cascade and hybrid
What causes the Ideal 9.1.5 fault?
This fault occurs when the main temperature sensor responsible for monitoring the shared water supply becomes unresponsive or provides an impossible reading. The most common reason is a physical failure of the internal sensing element, though it can also be triggered by loose or corroded electrical connections between the sensor and the main control board.
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 →Ideal models that show the 9.1.5 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 9.1.5 fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026