BoilerFaultCodesThe 5 most common faults
01
Low water pressure High DIY-safe
Your boiler has switched itself off because the water level inside the heating system has dropped too low to operate safely.
What to try first
Locate the external filling loop, which is usually a silver braided hose under the boiler.Open the small valve or tap attached to the loop slowly, allowing water to enter the system while watching the pressure gauge.Stop filling once the needle reaches the green zone, typically between 1.0 and 1.5 bar, then ensure the valve is fully closed.
02
F1 High Engineer
Your boiler is trying to start up but cannot light the gas flame needed to produce heat.
Full guide for F103
F2 High Engineer
Your boiler has lost the ability to accurately measure the water temperature, so it has safely shut down to prevent overheating.
Full guide for F204
Overheat High Engineer
Your boiler has detected that it is getting dangerously hot and has automatically shut itself down to prevent damage.
Full guide for Overheat05
Lock-out High Engineer
Your boiler has stopped working as a safety precaution because it either failed to light or became too hot.
Full guide for Lock-outon the Heatline Capriz 28
Pressure relief valvePressure sensorExpansion vesselIgnition leadIgnition electrodeGas valve
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 Heatline 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