BoilerFaultCodesThe 6 most common faults
Your boiler is overheating because the water inside is heating up faster than it can be moved around the system.
Why it happens: This fault occurs when the heat inside the boiler cannot be carried away quickly enough, causing the internal temperature to spike dangerously fast. The most common reasons are a failed pump that isn't pushing water through the pipes or a blockage, such as sludge or limescale, that is restricting the flow. Essentially, the boiler is generating heat but has nowhere to send it, so it shuts down to prevent damage.
Check that all radiator valves are fully openEnsure the boiler pressure is between 1 and 1.5 bar on the pressure gaugeCheck if the pump is running or if there are any obvious signs of a leak
Your boiler has entered a temporary lock-out mode because a service engineer's diagnostic tool was recently plugged in and has not been properly disconnected or reset.
Why it happens: This fault occurs when the boiler's internal computer remains in 'diagnostic mode' after being connected to a technician's service tool. It signifies that the communication between the boiler and the external hardware was interrupted or not closed down correctly, causing the system to stay frozen for safety. In most cases, it is simply a digital hang-up rather than a component failure.
Locate the reset button on the boiler control panel.Press and hold the reset button for 5 seconds.Wait for the boiler to complete its startup sequence; if the code persists, a technician may need to re-insert and properly exit their diagnostic software.
Your boiler has started up but cannot detect the water getting any hotter, so it has shut down to prevent overheating.
Why it happens: This fault occurs when the boiler fires up but the internal sensors don't see the water temperature increasing as expected. The most common reason is that water isn't moving through the system quickly enough, often due to a seized pump or a blockage in the heat exchanger. Because the heat has nowhere to go, the boiler shuts down immediately to protect its internal components from overheating.
Check that your central heating valves under the boiler are fully openEnsure all your radiator valves (TRVs) are turned to a high settingCheck your system pressure is between 1 and 1.5 bar and top up if necessaryBleed your radiators to remove any trapped air pockets
Your boiler has stopped working because there is not enough water pressure in the system to operate safely.
Why it happens: This fault occurs when the water pressure inside your heating system drops below the minimum level required for the boiler to fire up. The most common reasons are a slow leak from a radiator valve or pipework, or the air pressure in the expansion vessel has depleted over time, causing water to be expelled through the safety valve.
Locate the internal or external filling loop (the silver braided hose)Slowly open the valve(s) to allow water into the systemClose the valves once the pressure gauge reaches 1.5 bar
A safety switch or an external control, such as a thermostat or a condensate pump, has tripped and told the boiler to stop running.
Why it happens: This fault occurs when a safety device connected to the boiler’s control board has broken the electrical circuit to stop the unit from running. The most common reason is a blocked condensate pump that has reached its limit and sent a signal to prevent an overflow, or an external thermostat that has malfunctioned. Essentially, a secondary safety device has stepped in to shut the system down for protection.
Check if your thermostat or programmer is calling for heat and has working batteries.If you have a condensate pump, check if it is full of water or blocked.Ensure all external switches or emergency stop buttons near the boiler are in the 'On' position.
Your boiler is heating up too quickly, which usually means the water inside is not circulating properly or the system is low on pressure.
Why it happens: This fault occurs when the heat exchanger gets too hot too quickly because water isn't moving away from it fast enough. The most common reasons are a failing circulation pump, a blockage in the pipework, or air trapped within the system preventing the flow of water.
Check the system pressure gauge and top it up to 1.5 bar if it is too lowEnsure all radiator valves are fully open to allow water to flowBleed all radiators to remove trapped air that might be blocking circulation
on the Worcester Bosch GB162
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