BoilerFaultCodesThe 6 most common faults
Your boiler is failing to light the gas flame, meaning it cannot provide heating or hot water.
Check if your gas supply is active by testing another gas appliance like a hob.Ensure your gas meter has credit if you use a prepay meter.Press and hold the reset button for five seconds to see if the boiler restarts.
Your boiler has shut down because the air in your heating ducts is getting too hot, which can happen if air isn't flowing freely through your home.
Check that all warm air vents and registers in every room are fully open and not blocked by furniture or curtains.Inspect the return air grille (usually a large vent in a hallway) and ensure it is clean and unobstructed.Check the air filter (if accessible) and replace it if it is clogged with dust.
Your heater has detected that the air returning to the unit is too hot, causing it to shut down to prevent overheating.
Check that all internal room vents and grilles are open and unobstructedInspect the air filter and clean or replace it if it is clogged with dustEnsure no furniture or curtains are blocking the return air intake
Your heater is getting too hot because the air cannot flow through the system properly, causing it to shut down for safety.
Check all warm air vents throughout the house are fully open and not obstructed by furniture or curtainsInspect the air filter and clean or replace it if it is clogged with dustEnsure the return air grille is clear of any blockages
Your boiler thinks it sees a flame even though it hasn't started the ignition process yet, which prevents it from firing up for safety.
Full guide for E02Your boiler has shut down because it detected that it was getting too hot, and it has locked itself for safety.
Full guide for E03on the Johnson Starley C16d
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Johnson Starley shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue