BoilerFaultCodesThe 6 most common faults
Your boiler has detected that there is not enough water pressure or flow to operate safely, which is preventing your heating and hot water from working.
Why it happens: This fault occurs when the boiler's internal sensors detect that water is not circulating correctly or the pressure has dropped too low to operate safely. The most common reason is a simple loss of water pressure in the central heating system, but it can also be caused by a mechanical failure of the pump or a faulty sensor that is incorrectly reporting low pressure.
Check the pressure gauge on the front of the boiler; it should be between 1.0 and 1.5 bar.If the pressure is too low, use the external filling loop to top up the system with water.Ensure all radiator valves are open and bleed any air from the radiators.Turn the boiler off and back on again to reset the fault.
Your boiler has detected an internal temperature issue and has locked itself out to prevent overheating.
Why it happens: This fault occurs when the water inside the heat exchanger reaches an unsafe temperature, triggering a safety shutdown. It is usually caused by a lack of water flow, often due to a seized internal pump or a blockage within the system's pipework. If the pump cannot move the hot water away from the burner quickly enough, the heat builds up rapidly and trips the overheat sensor.
Locate the reset button on the front control panelPress and hold the reset button for at least 5 secondsCheck that your radiator valves are open and that the system pressure is between 1 and 1.5 bar
Your boiler has stopped working because water is not moving through the system properly, which is causing it to overheat and shut down for safety.
Why it happens: This fault occurs when the water inside the boiler gets too hot because it isn't being moved away quickly enough to the radiators. The most common reason is a failing internal pump that has stopped spinning, or a blockage of debris and sludge that is restricting the flow of water. It can also be caused by air trapped inside the unit which prevents the pump from working effectively.
Check that your system pressure is between 1.0 and 1.5 bar on the pressure gaugeEnsure all radiator valves and isolation valves under the boiler are fully openBleed your radiators to remove any trapped air that might be blocking circulationPress the reset button to see if the boiler restarts
Your boiler has stopped working because the fan is not receiving the correct electrical power needed to safely clear exhaust fumes.
Why it happens: This fault occurs when the boiler's main control board detects an incorrect voltage being sent to the fan motor. The most common reason is that the fan components have worn out and are drawing too much power, or the control board itself has developed a fault and can no longer regulate the electricity properly.
Full guide for 17Your boiler has failed to light, which means you will not have any heating or hot water until the issue is resolved.
Why it happens: This fault occurs when the boiler's internal computer tries to start the combustion process but cannot detect a flame. The most common reasons are a lack of gas reaching the burner, a faulty fan not clearing the flue, or a failing ignition component that cannot generate the spark needed to light the gas.
Full guide for 01Your boiler's internal thermometer for the central heating system has stopped working correctly, which means the system cannot monitor or control the water temperature.
Why it happens: This fault occurs when the boiler's central heating sensor either develops an electrical short or stops communicating with the main control board. The most common reason is that the internal thermistor has reached the end of its lifespan or has been damaged by constant temperature fluctuations, preventing the boiler from safely monitoring heat levels.
Full guide for 12on the Ravenheat CSI 120
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 Ravenheat 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