Nest Combi Boiler

Nest Combi Boiler

The Nest Learning Thermostat is capable of working with a wide range of systems. See article Nest Learning Thermostat to see compatibility.

For this article we will discuss the use of Nest Learning Thermostat with a combi boiler.

The Nest learning thermostat works very well with combi boilers. Essentially all combi boilers have a switching contact that brings the heating on, like a light switch. There are a few different types of interfaces. Following are some of the common ones.

• Zero Volt or Volt Free
• 240 v Switch live ( Can be part of a pair ie Live Supply and Live Return/Switched live.
• 24 volt
• Open Therm

230v Combi Boiler

The most common setup here in the UK is 230v switch live setup, where a 230v power supplied to the switch live terminal will cause demand for the heating side and fire the boiler. For this, live is supplied to terminal 2 of the heat link, either via the Live terminal on the Heatlink or via the Live Supply terminal on the boiler, and then terminal 3 of the heatlink will go to switch live on the boiler. See diagram below.

Low Voltage / volt free Combi Boiler

For zero volt / volt free and 24v interfaces, you would simply connect the pair to terminal 2 and 3. Usually terminal 2 will be your common or feed in and terminal 3 will be your feed out. See diagram below. No 230v main should be connected to a low voltage interfaces such as this.

OpenTherm Boiler

Finally OpenTherm is a special interface that allows 2 way communication between the Nest Thermostat / Heatlink and the Boiler. It’s an intelligent form of communication whereas the other interfaces are simply on/off switches. For more info on OpenTherm see our OpenTherm Capable Boiler page and Modulating Controls page.

Advanced Optimisation of Nest Learning Thermostat with a Combi Boiler

In order to gain the most out of this combination, of Nest Learning Thermostat with a combi boiler, you must make sure your heating system is well balanced. Radiators must be adjusted so that they distribute heat optimally and the rooms warm up effectively.

There is a setting on the Nest Thermostat called True Radiant. Usually switched on by default this tries to bring the heating on before it’s required to meet the target temperature set point for a particular time. Generally radiator based systems warm up in under 1 hour, so setting a maximum duration of 1 hour in the True Radiant setting will prevent the heating coming on too early.

A top tip, is that if you are able to make your house take a little longer to gradually warm up, then it will give more time for the Nest Thermostat to detect an even temperature throughout the rooms.  To do this, you need to reduce your flow temperature on the boiler to the lowest level such that your house will still warm up in colder months. It’s similar to a car in which your acceleration is gradual rather than rapid. You will gain comfort and energy savings by your house being allowed to absorb the heat.