BoilerFaultCodesIdeal H.....1..... Fault Code
Also written as H1 — same fault.
The Ideal H.....1..... fault code means: your boiler has detected an issue with the sensor that monitors the temperature of the water leaving the unit, preventing it from heating correctly.. It appears on 11 Ideal models in our database.
Technical description: FLOW THERMISTOR ERROR
What causes the Ideal H.....1..... fault?
This fault occurs when the internal sensor responsible for measuring the temperature of the water leaving the boiler fails to send a clear signal. The most common reason is that the sensor's electrical resistance has moved out of its normal range, or the wired connection between the sensor and the main control board has become loose or corroded. Because the boiler cannot accurately tell how hot the water is, it shuts down as a safety precaution to prevent overheating.
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 H.....1..... fault code
Click a model for the full fault code list and model-specific repair notes.
- Classic FF 330 Repair: £120-250
- Esprit HE Repair: £90-160
- Icos Repair: £90-160
- Icos HE Repair: £120-220
- Icos System Repair: £150-300
- Icos System Repair: £120-200
- Isar HE Repair: £120-200
- Isar M30 / M100 Repair: £120-220
- Isar System Repair: £120-200
- Mexico Super 100FF / 125FF Repair: £150-300
- Mexico Super 100FF / 125FF Repair: £120-220
Source
Ideal H.....1..... 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