If this is indeed the case, I don't think I can use the Nest unless I use some sort of relay, or change the valve.

Look at the wiring diagram for your make/mode of room thermostat that you are removing. If you don't have the instructions for it, a diagram is usually printed inside the lid. This will show which are the two switching wires, and which is the neutral wire. (If there is a neutral present. Not all thermostats need or have one fitted) unfortunately you can't rely on the wire colours.

Join the conversation about this product

An Example circuit diagram is shown below. This diagrams is schematic and should be used as a guide only. Designed for use with fully pumped central heating systems, using three separate two-port zone valves. PLEASE NOTE - Using this procedure will restore the ChannelPlus to the original factory programme settings, the time setting will also default to 1st January 2005. TIME AND DATE - The programmer has been pre-set with the current time and date during manufacture. No alteration should be required to the time and date, however if any modifiaction is required please refer to the 'Adjusting Time and Date' section of the user guide. Then, once the common at the Heatlink is connected, both devices will function identically to each other.

Finally on the programmer what would be the point in providing term 3 to be live when the heating was off. You will have to link the terminals L, and the two 'commons' 2 & 5 together at the Heatlink. [This link is made internally in the Horstmann]

Rating

Finally at least one radiator in the room where the Nest Thermostat is located should not be fitted with a TRV, otherwise it could interfere with the operation of the Nest and prevent it working properly. Once the mains power has been switched on the ChannelPlus H37XL Series 2's display will illuminate. The programmer has a number of pre-programmed functions to assist the installation, which are detailed below; ChannelPlus H37XL Series 2 Controlling 3 x two port spring return zone valves via RoomStat and CylinderStat giving independent control of Hot water and two zones of Heating.