BoilerFaultCodesThe 6 most common faults
01
37 High DIY-safe
Your boiler has stopped working because the amount of water inside your heating system has dropped below the minimum level required to operate safely.
What to try first
Locate the external filling loop, usually a small silver braided hose with one or two valves located underneath the boiler.Gradually open the valve(s) to allow mains water into the system while watching the pressure gauge on the front of the boiler.Stop filling once the needle reaches the green zone, typically between 1.0 and 1.5 bar, then ensure the valves are fully closed.
02
FAN FAULT High Engineer
Your boiler's air circulation system has stopped working, which means the device cannot safely ignite or produce heat.
Full guide for FAN FAULT03
12 High Engineer
Your boiler has detected an internal computer error that prevents it from starting safely.
Full guide for 1204
13 High Engineer
Your boiler has failed to light after several attempts and has locked itself out to prevent a build-up of unburnt gas.
Full guide for 1305
21 High Engineer
Your boiler's internal computer is struggling to read data from its sensors, which prevents it from safely controlling the heat.
Full guide for 2106
31 High Engineer
Your boiler has lost the ability to read the temperature of the water flowing through your heating system, so it has safely shut itself down.
Full guide for 31on the Johnson Starley Reno HE
Pressure sensor (transducer)Pressure gaugeFilling loopFan assemblyWiring harnessPCB
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