BoilerFaultCodesThe 6 most common faults
Your boiler has detected that there is not enough water in the central heating system to operate safely, so it has shut down to protect itself.
Why it happens: This fault occurs when the water levels inside your radiators and pipework drop below a functional level, meaning the boiler can no longer circulate heat safely. The most common reason is a tiny leak somewhere in the system or because the air was recently bled out of your radiators without topping the water back up. In some cases, a failing internal component like the expansion vessel may be causing the pressure to fluctuate and escape.
Locate the filling loop, which is usually a flexible silver hose with two small valves underneath the boiler.Slowly open both valve handles until you hear water entering the system.Watch the pressure gauge and close both valves tightly once the needle reaches 1.5 bar.
Your boiler has no power, which means it cannot turn on to provide heating or hot water.
Why it happens: This fault occurs when the electrical supply to the boiler is interrupted or fails to reach the internal control system. The most common reason is a blown fuse or a failed component like the EMC filter that has blocked the incoming power to prevent further electrical damage. It can also be caused by an external issue, such as a tripped circuit breaker in your home's main fuse box.
Check if other appliances are working to rule out a general power cutCheck your home fuse box for any tripped switchesEnsure the boiler's power switch or fused spur next to the boiler is turned on
Your boiler is failing to keep its small pilot flame burning, which means it cannot fire up to provide heating or hot water.
Why it happens: This fault occurs when the boiler's safety monitoring system fails to detect a constant pilot flame, causing it to shut down gas flow for safety. The most common reason is a worn-out thermocouple or a faulty overheat thermostat that is incorrectly sensing that the boiler is getting too hot.
Full guide for 52Your boiler's small starter flame is lit, but the main burner is failing to ignite because it isn't receiving the gas flow it needs to heat your home.
Why it happens: This fault occurs when the boiler successfully lights its small pilot flame but fails to transfer that flame to the main burner. The most common reason is a mechanical failure within the gas valve or a faulty electronic command from the control board, preventing the main flow of gas from being released. It essentially means the ignition process has started, but the 'full' heat cannot be triggered.
Full guide for 53Your boiler’s internal computer has encountered a critical failure and can no longer control the heating system safely.
Why it happens: This fault occurs when the boiler's main control board suffers an internal electrical failure or memory corruption. The most common reasons are age-related wear to the board's capacitors or a sudden power surge that has damaged the delicate circuitry responsible for managing the boiler's safety sequences.
Full guide for LEYour boiler's hot water sensor is struggling to communicate with the main control board, meaning the system cannot accurately monitor the water temperature.
Why it happens: This fault occurs when the boiler's internal computer loses track of the hot water temperature because the sensor has failed or its wiring has become damaged. The most common reason is that the sensor has physically degraded over time or a loose connection has developed, preventing the boiler from safely heating your water.
Full guide for PCB 38 HW light flashingon the Ideal Classic FF
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 Ideal 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