Worcester 24i?

not all of these boilers have the optional plug in programmer. You don't say if the fault indicator light's flashing fast or slow, this doubles as the reset button, flash once per second you press button in for five seconds, flashing fast (five times per second) you turn the power supply off and on at the switch socket supply (wall plug)

peter o'toolbox
March 2017

There's a flap at the bottom - on the front - behind it is a window where error messages are displayed.

Check the manual - The User Instructions. Or call in a boiler specialist. Consider pressing the Reset Button first.

Good Luck...
March 2017