BoilerFaultCodesThe 6 most common faults
01
Pump has run dry. High DIY-safe
Your boiler has stopped working because it has lost the water pressure needed to circulate heat throughout your home.
What to try first
Locate the filling loop (usually a silver braided hose under the boiler).Slowly open the valves to let water in until the pressure gauge on the front reads between 1.0 and 1.5 bar.Close both valves tightly and restart the boiler.
02
A1 High DIY-safe
Your boiler has detected that there is not enough water circulating inside the system to operate safely.
What to try first
Check your boiler pressure gauge; if it is below 1 bar, you need to repressurise the system using the filling loopTurn the boiler off and on again (reset) once the pressure is back to the recommended 1.2 to 1.5 barCheck your radiators for trapped air and bleed them if necessary
03
Code plug not detected. High Engineer
Your boiler's computer has lost track of what specific model it is because a small plastic identification chip has become loose or disconnected.
Full guide for Code plug not detected.04
Fan speed too low. High Engineer
Your boiler has detected that the internal fan responsible for venting exhaust gases is not spinning fast enough, so it has shut down as a safety precaution.
Full guide for Fan speed too low.05
CH flow NTC sensor defective. High Engineer
Your boiler is struggling to read its own internal water temperature because a sensor has stopped working correctly, which will likely prevent it from heating your home.
Full guide for CH flow NTC sensor defective.06
Flame not detected. High Engineer
Your boiler is trying to start but the flame is not catching, so it has shut itself down as a safety precaution.
Full guide for Flame not detected.on the Worcester Bosch 532 / 537 / 542
Filling loopPressure gaugePressure relief valveCentral heating pumpPressure sensorCode plug
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 Worcester Bosch 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