Vaillant VRT 350F Programmable Room Thermostat, Heating Control, Wireless Thermostat, Programmable Thermostat, Temperature Controller

A room thermostat measures the air temperature and switches the heating on or off to hold the setting you choose. Wired thermostats are connected to the boiler or wiring centre by cable rather than by radio. This category covers simple dial and digital room thermostats, programmable room thermostats that add timing, and wired smart thermostats; some kits in the range also use a radio-linked receiver.

Key choices

• Programming: a plain thermostat holds one temperature; programmable models set times and temperatures on a 24 hour, 5/2 day (weekdays and weekend) or 7 day pattern.
• Power: some run from the mains supply, others from batteries while still switching a mains-voltage circuit.
• Switching: volt-free contacts switch a separate circuit and can be wired into systems of different voltages, so match the thermostat to the wiring you have.
• OpenTherm: a two-wire digital link that lets a compatible thermostat ask the boiler to turn its output up or down rather than simply on and off. Both the boiler and the thermostat must support it.

Fitting and regulations

Fit the thermostat about 1.5m above the floor, away from radiators, lights, televisions, direct sunlight, draughts and outside walls. Wiring should be done by a competent person to the current wiring regulations, with the supply isolated first. In England, when a boiler is replaced, Approved Document L expects time and temperature control and boiler interlock, so the boiler and pump switch off when nothing needs heat. For a gas combination boiler in an existing home, one extra measure is also required, such as a smart thermostat with automation and optimisation, load compensation or weather compensation.

For radio-linked models, see wireless thermostats, or browse heating controls.