How to use a typical boiler Analogue Time Clock; Worcester, Vaillant, Potterton, Glow Worm etc e.g. worcester m10 time clock, Vaillant timeswith 110, vaillant timeswitch 150.
To Set the Clock
Turn the entire outer ring of the dial clockwise until the correct 24 hour time of day is at the black arrow ▲ (e.g., in diagram, time shown is 8.30 a.m.)
Programming the Timer
To set the ON period, push the grey tappets towards the centre, from the start of the ON period until the end of the ON period. (Tappets in middle = ON. Tappets towards outside = Unit will be OFF)
The black arrow ▲on the inner ring is the one that sets the time for the unit. When programming the timer, the time shown by the clock hands should synchronise with the hour on the 24 hr ring arrow▲ e.g. 9 hrs (am) or 21 hrs (pm)
If your setting is 12 hours out, rotate the entire outer ring (containing the tappets) clockwise, until the alternative 'o'clock is aligned with the arrow.
In essence there are two clock the 24 hour clock on the outside with the time settings for the boiler. Then the 12 hour face clock on the timer (time clock) which serves no purpose other than to show you the time with a standard face clock.