BoilerFaultCodesIdeal Hn Fault Code
Also written as HN — same fault.
The Ideal Hn fault code means: your boiler has detected that the electrical wiring is connected the wrong way around, or there is a fault with the electronics that makes it think so.. It appears on 2 Ideal models in our database.
Technical description: PHASE REVERSAL ERROR
What causes the Ideal Hn fault?
This fault occurs when the boiler detects that the live and neutral electrical connections have been swapped, which is often caused by recent electrical work or a DIY mistake at the plug or fused spur. In some cases, it can also be triggered by a failing control board that is no longer able to correctly identify the incoming electrical polarity. Because it is a safety risk, the boiler will refuse to fire until the wiring is corrected or the faulty component is replaced.
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 Hn fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal Hn 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