BoilerFaultCodesThe 6 most common faults
Your boiler has reached an unsafe temperature and has shut itself down to prevent damage to the internal components.
Why it happens: This fault occurs when water cannot circulate through the boiler quickly enough to carry heat away, causing the internal temperature to spike. The most common reasons are a failed pump that isn't pushing water, a blockage caused by sludge buildup, or air trapped within the system.
Check if any radiator valves have been accidentally closed and open them fullyEnsure your system pressure is between 1 and 1.5 bar on the pressure gaugeGently bleed your radiators to remove any trapped air that might be blocking water flow
Your boiler has detected an issue with the cold water arriving at the unit, meaning it cannot safely heat water for your taps or shower.
Why it happens: This fault occurs when the boiler cannot detect a consistent flow or pressure of cold water entering the system. The most common reason is a blockage caused by grit or debris in the inlet filter, or a mechanical failure of the internal turbine that monitors water movement.
Check that the main water stopcock in your home is fully open.Ensure any isolation valves on the pipework leading to the boiler are turned to the 'on' position.Check with your local water provider to see if there is a supply outage or burst pipe in your area.
Your boiler has detected that the water pressure inside the system is too high, which can cause safety valves to leak or the unit to shut down.
Why it happens: This fault occurs when there is too much water in your heating system, placing excessive strain on internal components. The most common reason is that the filling loop has been left slightly open after topping up the pressure, though it can also happen if a component like the expansion vessel has failed and can no longer regulate water volume as it heats up.
Check that the filling loop valves are fully closedBleed a radiator to release excess water pressureMonitor the pressure gauge stays between 1 and 1.5 barEnsure the pressure relief valve is not dripping outside
Your boiler has detected that there is too much water in the system combined with high temperatures, causing it to shut down for safety.
Why it happens: This fault occurs when the internal water pressure becomes too high while the boiler is running, often caused by a faulty filling valve that is letting too much water into the system. It can also happen if the expansion vessel, which manages pressure changes as water heats up, has failed or lost its air charge. When these two factors combine, the boiler shuts down to prevent internal components from being damaged by the excessive force.
Check that the internal or external filling loop valves are fully closed.Bled water from a radiator bleed valve to reduce the system pressure.Monitor the pressure gauge to ensure it stays between 1.0 and 1.5 bar when cold.If pressure rises again without intervention, contact a Gas Safe engineer.
Your boiler has sensed it is getting too hot and has shut itself down as a safety precaution.
Why it happens: This fault occurs when the water inside the boiler reaches an unsafe temperature, forcing the system to shut down to prevent damage. The most common reasons are a pump failure that stops water from moving around the system or a build-up of debris causing a blockage in the heat exchanger.
Check that your radiator valves are open and not turned offEnsure there is enough water pressure in the system by checking the pressure gaugePress the reset button on the front of the boiler control panel
Your boiler has detected a problem with how it controls the gas flow, meaning it cannot safely regulate the flame and has shut down as a precaution.
Why it happens: This fault occurs when the boiler's main control board loses the ability to vary the amount of gas entering the burner, which is necessary to maintain the correct water temperature. The most common reason is an electrical failure in the solenoid coil that moves the gas valve, or a communication error from the circuit board itself. Because the system can no longer precisely control the size of the flame, it shuts down to ensure your home remains safe.
Full guide for E4on the Worcester Bosch WR325 RSF
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