Contents

1. What is a heating control?
2. How does it work?
3. Types of standard heating control:
   • Dial thermostats
   • Time clocks
   • Programmers
   • Programmable room thermostats
4. Types of advanced heating control
   • Smart controls (internet controls)
   • 'Automation and optimisation' controls
   • Compensation controls - load and weather
5. On/off v continuous heating controls
6. Heating control efficiency classes
7. Control requirements for new boilers
8. Thermostatic radiator valves (TRVs)
9. Smart radiator valves

1) What is a heating control

The term ‘heating control’ covers a wide range of products that automatically turn the boiler on and off, or adjust the output up and down, with varying degrees of sophistication. Heating controls can be a simple as a dial thermostat to an internet control that adjust the boiler in advance of outside weather changes.

2) How does a heating control work?

At the most basic level, a dial thermostat will be set to the desired temperature, say 21 degrees. When the room temperature drops below 21 degrees, the boiler will come on, which it reaches 21 degrees it will tell the boiler to switch off. Basic controls tend to overshoot the set room temperature by a degree or two and are less efficient than other controls.

At the opposite end, compensation smart controls will adjust the output of the boiler up and down in small increments to meet the room temperature exactly. These save energy and reduce fuel bills.

3) Types of standard heating control

Standard heating controls control time and temperature without any internet connection or 'learning' features.

Dial thermostats

The most simple of controls. A dial thermostat is located in the room you spend the most time in, i.e. sitting room, and set to the desired temperature – commonly 21 degrees. The boiler will come on when the temperature of the room drops a few degrees below the set temperature and turns off when it reaches 21 degrees.

Advantages

Cheap to buy and easy to set/adjust

Disadvantages

Not efficient as the boiler overshoots the set temperature by 1 or 2 degrees. The boiler is either on or off according to the room temperature with no options to turn the heating off during periods when you are out of the house.

Time clocks

These are usually located on the front of the boiler and offer a means of setting the times that a boiler can come one and off. The little pins are push in for the times that you want the boiler on. When used in conjunction with a thermostat this does offer reasonable control of your heating system.

Advantages

Cheap to buy and easy to set/adjust

Disadvantages

You cannot change the times the boiler comes on and off according to the day of the week.

Programmers

Digital programmers allow for the boiler to be programmed to come on and off at different times of the day. 7 day programmers and 5/2 day programmers allow for the times to be set at different times on every day of the week or to set different times for weekdays and weekends.

Programmers have 1, 2 or 3 'channels'. The ‘channel’, like a radio channel, is the means by which the unit communicates with the boiler.

• Single-channel programmers are used with combi boilers and they only control the heating.
• Twin-channel programmers work with heat only or system boilers and control the heating and hot water cylinder or combi boilers with two heating zones.
• Three-channel programmers also work heat only or system boilers but can control two heating zones as well as hot water.

Advantages

More flexibility to set different times for different days

Disadvantages

More difficult to set up and often need the help of a heating engineer.

Programmable room thermostats

A popular option for modern heating systems as it combines daily programming of times the boiler is on and to what temperature. Also referred to as ‘time and temperature controls’ these combined units, as well as separate units, meet current building regulation requirements for new heat-only and system boilers (i.e. those boilers that work with a hot water cylinder). We provide a full review of programmable room stats products in our Guide to programmers

Advantages

Combined unit offers more flexibility

Disadvantages

More difficult to set or change and often needs the help of a heating engineer

4) Types of advanced heating control

Advanced heating control are usually connected to the internet, although not always, and used AI (artificial intelligence) to work out your patterns of use to improve the operation of the boiler and reduce fuel bills. Some models also control the output of the boiler to use less fuel.

Smart - internet - controls

This is a big group. The common feature is that they connect to the internet and can be controlled remotely. However some are not more than a basic programmable room thermostat (such as Hive) and others offer advanced features that really maximise the boiler’s efficiency (see compensation controls section below). For more on products try our Comparison guide to smart control products

Advantages

Combined programmable room thermostat with remote access to turn on and off via a smart phone.

Disadvantages

Requires a modem and smartphone.

Automation and optimisation controls

Automation and optimisation is a category under 'Boiler Plus' that covers a range of functions that automate the time and temperature settings based on occupancy detection, geolocation and/or stored data from user patterns over time.

Many smart controls work on a learned schedule of use (often referred to as a ‘learning’ capability) and how quickly your home loses or gains heat. Over time the control will know how early the boiler will need to come on to meet the set temperature. NB not all Automation and Optimisation controls are internet controls. For help on product selection see our Guide to Boiler Plus controls

Advantages

Compatible with all boilers.

Disadvantages

Not as efficient as other forms of advanced control

Compensation controls - load and weather

All modern boilers are ‘modulating’, which means they can adjust their output up and down to meet the heat requirement and automatically adjust the flow temperature to your radiators. This saves gas and reduces fuel bills. However they can only reach their maximum efficiency when paired with compensation control that speaks the same language as the boiler. In order to fit a compatible compensation control you must either:

1) Fit the boiler manufacturer’s own compensation control, or

2) Fit a boiler and control that both use the OpenTherm language. Opentherm is a language developed by Honeywell that boiler and control manufacturers can adopted in order to make their products compatible. For more see our Guide to Opentherm boilers and controls

There are few types of types of modulation control: load compensation, weather compensation and combined load and weather compensation controls. The combined load and weather compensation units are the most efficient and deliver the most stable room temperatures. To review all load and weather compensation controls by product, see our Guide to the best smart controls.

Advantages

Maximise the efficiency of the boiler.

Disadvantages

Product selections are limited by compatibility.

5) On/off v continuous heating controls

There are two main methods of setting up a central heating system depending on the ErP source (i.e. gas boiler, oil boiler, biomass boiler, electric boiler or heat pump).

• On/off systems. Older style gas and oil boilers were designed to work with on/off controls. In this set up, the boiler puts out great blasts of heat for short periods to get the home up to temperature quickly and then switches off. As a result, radiators get really hot for short periods.
• Continuous heating. Heat pumps and underfloor heating systems always work on a continuous heating set up whereby the heat pump or boiler is on most of the time but at a much lower temperature. Gas and oil boilers can also be set up to run in this way and in fact modern condensing boilers should be set up to run at lower temperatures in order to achieve the efficiencies ‘on the box’.

6) Heating control efficiency classes

The different types of heating control can be categorised according to efficiency. The ErP control classes (I-VIII) have been reviewed and adjusted by UK bodies to determine the effectiveness of the control type for improving efficiency. (NB Class III and VII are not used).

Class I - on/off controls:

• Dial thermostats

• Standard programmable room thermostats

• Programmable room thermostats with internet function (such as Hive)

• Some automation & optimisation controls

Class V - Load compensation 

Class VI - combined weather and load compensation 

7) Controls for new boiler installations

Boiler Plus was introduced in 2018 and requires that some form of advanced control is fitted with new combi boilers and ‘time and temperature’ controls (aka programmable room thermostats) are fitted with heat only and system boilers. If you are have a new combi boiler fitted, your installer must fit an advanced heating measure from the following list:

• Load compensation

• Weather compensation

• Automation and optimisation

• Flue gas recovery unit

As the Control Classes table shows, some controls are more efficient than others. The higher efficiency controls - V, VI and VIII - must speak the same language as the boiler. Class I controls will work with all boilers, but they are less effective in terms of efficiency. For more information try our Guide to advanced controls and Boiler Plus

8) Thermostatic radiator valves TRVs

Thermostat radiators valves are important for controlling temperatures in individual rooms and reducing the heat requirement across the home. Standard TRVs cost around £12.50, but there are many other styles available. We've developed a comprehensive Guide to TRVs where we bring together all products and group them according to style and budget.

9) Smart radiator valves

An evolution of the thermostatic radiator valve is the smart radiator valve. They come in a few different forms, but the most common are those that work with a compatible advanced heating control. Each of the valves can be programmed via the main control. The combined control and radiator valves (minimum of three) can create a Class VIII control. For more help go to our Guide to smart radiator valves.