BoilerFaultCodesIdeal H n Fault Code
Also written as HN — same fault.
The Ideal H n fault code means: your boiler has detected that the electrical wiring coming into the unit is swapped or incorrectly connected, preventing it from starting safely.. It appears on 15 Ideal models in our database.
Technical description: PHASE REVERSAL
What causes the Ideal H n fault?
This fault occurs when the live and neutral electrical wires leading into the boiler have been accidentally swapped, usually following electrical work in the home or a smart thermostat installation. The boiler's safety sensors detect that electricity is flowing in the wrong direction and prevent the unit from firing to avoid damage or electric shocks. In rarer cases, a fault within the internal control board can cause it to misinterpret correct wiring as a reversal.
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 n fault code
Click a model for the full fault code list and model-specific repair notes.
- Classic FF Repair: £80-160
- Classic FF 330 Repair: £90-160
- Esprit HE Repair: £80-120
- Esprit HE Repair: £90-180
- Icos Repair: £80-160
- Icos HE Repair: £80-150
- Icos HE Repair: £90-160
- Icos System Repair: £150-300
- Icos System Repair: £90-150
- Isar HE Repair: £120-250
- Isar M30 / M100 Repair: £150-300
- Isar System Repair: £120-250
- Mexico HE Repair: £80-160
- Mexico Super 100FF / 125FF Repair: £180-350
- Mexico Super 100FF / 125FF Repair: £90-160
Source
Ideal H n 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