BoilerFaultCodesThe 6 most common faults
Your boiler has failed to ignite, which means it cannot provide any heating or hot water until it is reset or repaired.
Check that your gas pre-payment meter (if you have one) has credit.Ensure that the gas supply valve to the boiler is open.Press and hold the 'R' or 'Reset' button for a few seconds to try and restart the sequence.
Your boiler has stopped working because the water pressure is too low for it to operate safely.
Locate the filling loop (usually a silver flexible hose) underneath your boiler.Slowly open the valve or valves on the filling loop until you hear water flowing.Watch the pressure gauge on the boiler until it reaches between 1.0 and 1.5 bar, then close the valves fully.
Your boiler has failed to ignite or detect a flame, causing it to shut down for safety.
Press the Reset button (control key 2) to attempt a restartCheck that your gas meter has credit and the gas emergency control valve is openCheck if other gas appliances, like a cooker, are working correctly
Your boiler has experienced an ignition failure and cannot start up to provide heat or hot water.
Check that your gas pre-pay meter has credit (if applicable).Ensure other gas appliances in your home, like a hob, are working correctly.Press the Reset button (control key 2) on the boiler panel to attempt a restart.
Your boiler has stopped working because water is not flowing through the system correctly.
Check that all radiator valves are fully openEnsure the blue handled isolation valves under the boiler are in the open positionCheck if the system pressure is too low and top up if necessary
Your boiler has detected low water pressure in the system, which means it cannot circulate water safely or effectively.
Locate the filling loop (usually two blue levers or a braided hose) under the boiler.Slowly open the valves until you hear water flowing and the pressure gauge reaches between 1.0 and 1.5 bar.Close both valves completely and press the reset button on the control panel.
on the Sime iQE Simplicity 20T
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