BoilerFaultCodesIdeal 4.12 Fault Code
Also written as 412 — same fault.
The Ideal 4.12 fault code means: your boiler has stopped working because it cannot detect water moving through the internal pipes to keep the system safe.. It appears on 8 Ideal models in our database.
Technical description: No Water Flow
What causes the Ideal 4.12 fault?
This fault occurs when the boiler's internal sensors do not detect enough water movement to safely heat the system, causing it to shut down to prevent overheating. The most common reasons are a failed circulation pump that can no longer push water through the pipes, or a blockage caused by a build-up of debris and sludge. It can also be triggered if the water pressure is too low or if air is trapped inside the heat exchanger.
This fault often appears when the heating is first turned on in autumn, as pumps can seize up after sitting idle throughout the summer months.
DIY fix possible
Check the pressure gauge on the front of the boiler is between 1 and 1.5 barIf the pressure is low, use the filling loop underneath the boiler to top it upEnsure all radiator valves and isolation valves under the boiler are fully openPress the Restart button to clear the fault
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Gas Safe Register →Ideal models that show the 4.12 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 4.12 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