BoilerFaultCodesThe 6 most common faults
01
117 High DIY-safe
Your boiler has detected that the water pressure inside your heating system is currently too high for safe operation.
What to try first
Locate a radiator in your home, preferably one upstairs.Using a radiator bleed key, open the bleed valve slightly until a small amount of water comes out to release pressure.Check your boiler's pressure gauge and ensure the needle has dropped back into the green zone (usually 1.0 to 1.5 bar).
02
118 High DIY-safe
Your boiler has stopped working because the amount of water circulating inside your heating system has dropped below the required level.
What to try first
Locate the filling loop (a silver flexible hose) underneath the boiler.Open the valves at both ends of the hose to allow water into the system.Watch the pressure gauge on the front of the boiler until the needle reaches 1.5 bar, then firmly close both valves.
03
20 High Engineer
Your boiler has lost the ability to accurately measure the temperature of the water circulating to your radiators, so it has shut down to prevent overheating.
Full guide for 2004
28 High Engineer
Your boiler's safety sensor that monitors the temperature of the exhaust gases has failed, so the system has shut down to prevent overheating.
Full guide for 2805
40 High Engineer
Your boiler has lost the ability to accurately measure the temperature of the water returning to it, so it has safely shut down to prevent overheating.
Full guide for 4006
109 High Engineer
Your boiler is struggling to pump water around your heating system correctly, which is preventing it from staying on safely.
Full guide for 109on the Baxi 200 / 400 Combi
Pressure relief valveFilling loopPressure sensorExpansion vesselCentral Heating NTC SensorWiring harness
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 Baxi 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