BoilerFaultCodesThe 6 most common faults
01
Low Water Pressure High DIY-safe
Your boiler has stopped working because the water level inside the heating system has dropped too low.
What to try first
Locate the external filling loop, usually two silver valves connected by a small braided hose near the boiler pipes.Open the valves slowly to allow water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Fully close both valves and check the boiler for any leaks.
02
77 High DIY-safe
Your boiler has stopped working because the water pressure inside the system has dropped too low.
What to try first
Locate the filling loop valves connected to your boiler.Open the valves gently to allow water to enter the system until the pressure gauge reads between 1 and 1.5 bar.Close both valves firmly and check the gauge holds steady.
03
16 High Engineer
Your boiler has failed to light the flame, so it has safely shut itself down to prevent a build-up of unburnt gas.
Full guide for 1604
Overheat Lockout High Engineer
Your boiler has detected that it is running too hot and has automatically turned itself off to prevent damage.
Full guide for Overheat Lockout05
Ignition Lockout High Engineer
Your boiler has stopped trying to start up because it cannot detect a flame to safely heat your home.
Full guide for Ignition Lockout06
Flame Loss High Engineer
Your boiler has safely shut down because the internal burner flame has unexpectedly gone out.
Full guide for Flame Losson the Keston Heat 55
Filling loopPressure relief valvePressure sensorAuto air ventIgnition 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 Keston 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