When the system pressure is too low on a Worcester boiler it is designed to prevent the boiler from firing so as not to cause damage to the appliance should there be a problem with the system. Nine time out of ten the problem is quickly cured by topping up the pressure. System pressure drop is often caused by someone venting air from radiators or small leaks from the central heating system.
To reinstate the pressure you will require a charging key which should be left with boiler by the installer. If you have no key you can simply purchase one from MDS plumbers Merchants and Gas Spares Stockists. Simply follow the instructions in your users guide. However should the system pressure keep dropping and requires frequent topping up then you must contact a engineer to find and repair the source of the leak. You can cause problems with boiler if you keep charging the system frequently. Boiler pressure should be about one bar when cold.