BoilerFaultCodesThe 6 most common faults
Your boiler's internal water pressure is too low, meaning there is not enough water circulating to heat your home or provide hot water.
Locate the external filling loop (a flexible metal or braided hose) connected to your boiler's pipeworkOpen the valves on the filling loop to allow cold mains water to enter the systemMonitor the pressure gauge on the boiler front until it reaches between 1.0 and 1.5 bar, then close the valves tightly
Your boiler has detected that the water pressure inside the system has dropped too low for it to operate safely.
Locate the external filling loop (a metal braided hose connected to two valves under the boiler)Open both valves slowly until the pressure gauge on the boiler front reads between 1.0 and 1.5 barClose both valves tightly and restart the boiler
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Locate the external filling loop, which is a silver braided hose connected between two pipes near your boiler.Open the small valves at both ends of the hose to allow mains water into the system while watching the pressure gauge.Close both valves firmly once the needle on the pressure gauge reaches the green zone, typically between 1.0 and 1.5 bar.
Your boiler has detected an issue with the water flow or pressure sensor, causing it to shut down to prevent potential damage to the internal components.
Full guide for E3Your boiler is failing to detect that the water is circulating properly, which prevents it from safely heating up.
Full guide for E4Your boiler has detected an issue with the air supply or exhaust system, preventing it from operating safely.
Full guide for E5on the Sime Murelle HE Regular
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 Sime 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