An electronic service interval programmer controls central heating and hot water and helps landlords of social housing schemes comply with the UK Gas Safety (Installation and Use) Regulations 1998. It gives advance warning of the annual boiler safety check due date. Some models switch the central heating and domestic hot water on and off at the same time; while others allow the domestic hot water and heating to come on and go off at different times. You can set the ‘on’ and ‘off’ time periods to suit your lifestyle.