Drayton SM1 is a single-channel programmer. Utilising the more traditional rotating time wheel with pegs for settings, this easy-to-understand mechanical timer is suitable for use on most domestic pumped and gravity central heating systems. Drayton's SM1 single channel 24 hours electro-mechanical time switch gives style and ease of use to suit most domestic combination boiler systems. The SM1 is a 24 hour electro-mechanical timeswitch that offers style and ease of use for most domestic combination boiler systems.