This electronic trv 8 up to 28 c honeywell rondostat hr20 lets you decide what temperature you would like on what day and at what time of the day you can set programmes for individual days or for groups of days with up to four possible programmes per day you can of course change the program at any time by turning the rondostat knob the thermostat is simple to install and to operate as the thermostat is simply screwed onto the existing valve without opening the heating circuit suitable