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The Benefits of OpenTherm Connectivity

Blog30 October 2019

OpenTherm is a system of communication between modulating heating appliances and room thermostats which is not manufacturer dependent. It consists of a communication protocol and an interface specification which combine simple installation procedure with high functionality.

Traditional on/off thermostats can be easily interchanged, regardless of whether they are regular thermostats, programmers or clocks. The same applies to their compatibility with central heating appliances with simple on/off connections for controls. This allows a wide choice to installers when selecting the components of a heating system. However, when manufacturers of heating systems apply extra functions, more sophisticated communication protocols are needed. This means that many products are no longer interchangeable, and only heating products using the same manufacturer-specific protocol can be used together.

OpenTherm protocol is best summarised as a multi point-to-point communication protocol for use in residential heating. It requires a standard 2-wire low voltage and polarity-free connection and can also be used as a wireless protocol. It guarantees a minimum level of compatibility. Product documentation should state which system functions are available for particular combinations of products. Any extra functionality resulting from using OpenTherm is determined entirely by the manufacturers of the central heating products.

The basic function which every OpenTherm controller must provide is the communication of the heat requirement to the heating appliance. This heat requirement is calculated by the controller based on the difference between the set (or target) temperature and the actual temperature. If an OpenTherm weather compensator (outside temperature sensor) is connected, then the outside temperature is used to determine the heating requirement. Some of the standardised functions available include setting and reading DHW temperature, reading outdoor temperature and reading fault codes.

OpenTherm protocol is controlled by the OpenTherm Association, of which Ideal Boilers is a member. Ideal Logic boilers have OpenTherm wiring connections meaning operation is optimised when an OpenTherm room thermostat or programmable room thermostat (PRT) is connected. The central heating requirement is calculated, and the boiler will operate at the minimum rate at which this can be achieved which maximises operating efficiency and reduced fuel costs. It also maximises room comfort as the boiler output is reduced as the set temp is approached, so reducing overshoot and unnecessary overheating.

Using an OpenTherm room thermostat or PRT with all current Ideal domestic boilers gives easy compliance with Boiler Plus legislation. This includes the additional energy efficient measures when replacing a combi boiler as enhanced load compensation is achieved. Alternatively, an OpenTherm weather compensation device can also meet these additional measures.

For fully optimised operation of an Ideal Logic boiler an Ideal OpenTherm room thermostat should be used, such as the new Ideal Halo Lite OpenTherm Wired Combi. This has been developed to work seamlessly with Ideal Logic Combi C, Combi ESP1 and Code Combi ESP1 boilers and offers additional functionality which would not necessarily be available with other room thermostats such as fault information available in plain English on the control screen.

A modern looking control with an easy to use dial and button user interface and clear screen, the Ideal Halo Lite OpenTherm Wired Combi has been designed and tested with social housing tenants. Packed full of features such as flexible scheduling with up to 6 heating events, holiday mode, override and plus hours it allows tenants full control of the time and temperature of their heating.

For the landlord it’s a simple install and combines the convenience of a wired control with no batteries with the benefits of OpenTherm, including Enhanced Load Compensation for Boiler Plus compliance. Fault alerts on the screen and plain English fault descriptions, service reminders and useful landlord functions such as a service timer with pin number and child lock all make this control an easy choice

When it comes to heating controls simple and efficient is best and the new Halo Lite control combines both with a modern, clean design.