BoilerFaultCodesIdeal 39 Fault Code
The Ideal 39 fault code means: your boiler has lost communication with your wall thermostat, meaning it cannot receive the signal to turn on your heating.. It appears on 1 Ideal model in our database.
Technical description: Check the ModuLine room thermostat. If the thermostat functions properly, the control panel is defective. Replace the control panel.
What causes the Ideal 39 fault?
This fault occurs when the digital communication link between your wall controller and the boiler's internal computer is broken. The most common reason is a wiring failure at the connections or an internal electronic failure within the ModuLine thermostat itself, which prevents the boiler from receiving the command to fire up.
DIY fix possible
Check if your wall thermostat has run out of batteries and replace them if necessaryEnsure the thermostat is turned up higher than the current room temperatureReset the boiler by turning the control knob to the 'reset' position for five seconds
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Gas Safe Register →Ideal models that show the 39 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 39 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