OpenTherm Boiler Controls

'OpenTherm' is a communications protocol developed by Honeywell that can be used in central heating systems where a gas condensing boiler and controller communicate with each other allowing either weather compensation or load compensation to  increase the efficiency by continuously adjusting the boilers water flow temperature to match the controllers desired set point, keeping flow temperatures lower for longer raising the boilers condensing capability.

Thermostats which operate with a traditional ON/OFF system are unable to adjust the boilers water flow temperature leading to boiler cycling and overshooting of room temperatures. Most basic controllers can be upgraded as long as your current boiler also incorporates 'OpenTherm'.

Some boiler manufacturers such as Viessmann, Ideal, Baxi, ATAG, Ferroli and InterGas use 'OpenTherm' technology, while these boilers all sell their own branded controllers they are also compatible with some 3^rd party controllers on the market such as Honeywell, Drayton, Nest, Tado and EPH Controls.