BoilerFaultCodesTechnical description
No heat demand. Room thermostat, mains programmer (or link), or electronic programmer at ST5 failure. Red diode may be damaged.
What causes this fault?
This fault occurs when there is a break in the communication link between your controls and the boiler's main computer. It typically happens because the mechanical timer has worn out or the batteries in your wall thermostat have died, meaning the boiler never receives the 'on' command. In some cases, the internal electronic board that processes these signals has developed a fault and can no longer recognize when heat is being requested.
This issue is frequently seen during the first cold snap of autumn when homeowners try to turn their heating back on after it has been switched off all summer.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.