BoilerFaultCodesThe 6 most common faults
Your boiler has lost its flame while it was supposed to be running, causing the system to shut down for safety.
Why it happens: This fault occurs when the boiler's control system can no longer detect a flame while the unit is trying to heat your home. It is often caused by a dirty or worn-out sensor that can't see the fire, or a faulty gas valve that isn't providing enough fuel to keep the burner lit. Because the boiler cannot confirm it is burning gas safely, it shuts down entirely to prevent unburnt gas from building up.
Check if other gas appliances, like a hob, are working to ensure gas is reaching the propertyCheck if your gas meter has credit (if applicable)Press the reset button once to see if the boiler restarts
Your boiler has switched itself off because it has become too hot to operate safely.
Why it happens: This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety switch to prevent damage. The most common reasons are a failed pump stopping water from circulating or a build-up of sludge and debris blocking the internal pipework. It can also be caused by a faulty internal sensor incorrectly reading the temperature.
Turn the boiler off and allow it to cool down for at least 30 minutes.Ensure all radiator valves are open and there is no air trapped in the system.Unscrew the small black cap on the front control panel and press the reset button firmly.
Your boiler is automatically shutting down because it has detected dangerous exhaust fumes backing up into your home instead of escaping safely through the chimney.
Why it happens: This fault occurs when a safety sensor detects that the hot exhaust gases are not rising correctly through the chimney and are instead spilling back into the room. The most common reason is a blockage in the flue, a damaged chimney liner, or poor atmospheric conditions that prevent the natural pull of the chimney. Because these fumes contain carbon monoxide, the boiler shuts down immediately to prevent a dangerous build-up in your home.
Full guide for TTB constant tripYour boiler has become too hot and has automatically turned its pilot light off as a safety measure to prevent damage.
Full guide for Overheat conditionYour boiler has detected that hot exhaust fumes are not escaping properly through the flue and has switched itself off to prevent poisonous gases from entering your home.
Full guide for TTB TripThis light simply shows that your boiler is receiving electrical power and is switched on.
Why it happens: This is a normal status indicator rather than a fault, confirming that the internal control board is receiving 230v mains electricity. If this light is off, it usually means the boiler has blown a fuse, the external isolation switch is turned off, or there is a failure in the local power supply. As long as this light is glowing, the boiler has the electrical power it needs to begin the ignition sequence.
Ensure the main power switch for the boiler is in the 'ON' positionCheck that the fuse in the spur hasn't blown if the light fails to illuminateMonitor the boiler for normal operation as this light indicates standard power status
on the Potterton Osprey CF 125
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 Potterton 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