BoilerFaultCodesThe 6 most common faults
Your boiler appears to have no electrical power at all, meaning the screen and lights are completely blank and it will not provide any heating or hot water.
Why it happens: This fault occurs when the boiler's electrical circuit is broken, preventing the internal components from receiving the electricity they need to operate. The most common reason is a blown fuse on the main control board, often caused by a power surge or a failing internal part like a pump or valve short-circuiting the system.
Check if your home's main electrical consumer unit (fuse box) has tripped a circuit.Locate the boiler's fused spur (a wall switch near the boiler) and ensure it is switched on.Check the fuse inside the wall-mounted spur switch and replace it with a 3-amp fuse if necessary.
Your boiler is receiving power and trying to work, but it has failed to start the burner to provide heat or hot water.
Why it happens: This fault occurs when the boiler is receiving an electrical signal to start, but the internal sequence to light the flame is interrupted. It is often caused by a lack of spark from the ignition electrode or a failure in the internal fan which clears waste gases. In some cases, the gas valve may not be opening correctly to allow fuel into the burner, preventing the boiler from firing up.
Check if your thermostat is set higher than the current room temperatureEnsure your external programmer or timer is set to 'On'Check that the gas supply to the property is turned onPress the reset button on the front of the boiler
Your boiler has got too hot and has automatically shut down for safety to prevent damage.
Why it happens: This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety sensor to cut the power. It is usually caused by a pump failure that stops water from moving or a blockage in the system that prevents heat from being carried away fast enough. In some cases, air trapped in the heat exchanger can also cause a localized hotspot that trips the sensor.
Check that your radiator valves are open to allow water to circulate.Ensure your system pressure is correct (usually between 1 and 1.5 bar).Press the reset button on the front of the boiler once it has cooled down.
Your boiler has failed to light, which most likely means the gas supply is interrupted or there is a blockage preventing the burner from starting.
Why it happens: This fault occurs when the boiler attempts to ignite several times but fails to detect a flame, causing the system to shut down for safety. The most common reasons include a lack of gas reaching the burner, worn-out spark electrodes, or a buildup of carbon on the sensor that 'sees' the flame.
Check if your gas meter has credit or if other gas appliances in the house are working.If it is freezing outside, check if the white plastic condensate pipe leading outdoors is frozen and thaw it with warm water.Press the Reset button on the boiler for five seconds to see if it restarts.
Your boiler's internal computer has encountered a glitch or a hardware failure, preventing it from running properly.
Why it happens: This fault occurs when the boiler's main control board loses its ability to process data correctly or experiences a communication breakdown between internal components. It is often caused by a sudden electrical surge, moisture entering the control box, or simply the natural degradation of the solder points and microprocessors over time.
Switch the boiler off at the fused spur or power switchWait 30 seconds and switch the power back onPress and hold the Reset button for 5 secondsIf the code persists, contact a Gas Safe engineer to inspect the internal electronics
Your boiler has detected a critical internal error with its fan or electronic memory and has shut down for safety.
Why it happens: This fault occurs when the boiler's main computer loses communication with the fan or the small electronic chip that stores the appliance's settings. The most common reason is an electrical failure within the fan motor or a loose connection on the internal circuit board that prevents the boiler from safely managing the airflow. Without this constant data exchange, the system shuts down immediately to prevent an unsafe build-up of gas.
Full guide for Fast flashon the Worcester Bosch Greenstar Ri
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