heating Control Basics.
Controls come in various forms. In this section, we focus on the controls used in homes to manage heating systems. Modern controls have evolved beyond simple on/off switches, incorporating smart features and connectivity for greater efficiency and convenience. Gas boilers have to be installed to a standard called boiler plus, which sets out certain regulations to improve efficiency. Boiler plus document here
Part L states Each room will be fitted with a thermostat controller, this means adding TRVs to every radiator. Except those in whichever room houses the central thermostat.
Every heating system requires a way to monitor the ambient temperature, this is done using room thermostats.
While the thermostat doesn’t directly control the radiators, it signals the boiler when the desired temperature has been reached, prompting it to turn off or reduce output. When the temperature drops below the set limit, the boiler switches back on to maintain the desired warmth. This cycle continues automatically.
In addition to the room thermostat, thermostatic radiator valves (TRVs) are installed on radiators to regulate their individual temperatures. Once a radiator reaches its set level (typically between 1 and 5), the TRV closes to prevent overheating. Different rooms can have different TRV settings based on personal preference and heating needs.
A heating system controlled by a room thermostat should have at least one radiator without a TRV—this is known as the control radiator. It helps regulate the room’s temperature without shutting off automatically like other radiators. Typically, the control radiator is placed in a hallway, where air changes frequently due to doors opening and closing. It should also be located in a room without additional heat sources, such as a fireplace or ovens etc.
Many modern room thermostats now include programmable heating schedules, allowing them to act as the primary control interface for the heating source, whether it’s a boiler, heat pump, or another system.
Heating systems housed in unheated spaces (garages etc) will usually have auxiliary thermostats to protect the system from freezing (frost stat). This is basically just a room thermostat set at a low setting within that space or connected to the pipework.
Thermostatic radiator valves (TRV’s).
A TRV, or thermostatic radiator valve, is a device that controls the temperature of a radiator by adjusting the flow of hot water. These can be standard or smart. Only one side of a radiator has a TRV, and the other has a restrict or valve called a lock shield, which can be used for system balancing and shutting off.
A smart thermostatic radiator valve (TRV) is a radiator valve that can be controlled remotely using a smartphone, tablet, or RF remote. The head of the TRV is what controls the temperature by forcing a pin to close the valve.
Most TRV heads can be interchanged, but the mechanical pin needs to be in good condition to continue working effectively.
Types of TRV’s.
- Wax capsule. Uses a wax plug to regulate the flow of hot water into a radiator.
- Liquid. Uses a liquid capsule which is more responsive to regulate the flow of hot water into a radiator.
- Smart. They can be controlled remotely to zone off parts of the property. Some can be used via smartphone apps.
How It Works.
- The thermostat continuously measures the radiator’s temperature.
- If the radiator temperature reaches the desired set point, it restricts the flow of water.
- If the radiator temperature falls below the desired set point, it allows the flow of water.
Room thermostats.
A room thermostat is a device used to regulate the temperature in a room by controlling the heating system. It measures the air temperature and switches the heating on or off to maintain the desired temperature set by the user.
Types of Room Thermostats.
- Mechanical (Analogue). Thermostats. Usually just on and off via moveable dials.
- Digital Thermostats. Typically just on and off with visual readings.
- Programmable Thermostats. Allow users to set temperature schedules for different times of the day.
- Smart Thermostats. They can be controlled remotely via smartphone apps and often use AI to optimize heating/cooling.
How It Works.
- The thermostat continuously measures the room temperature.
- If the temperature falls below the set point, it turns the heating system on.
- If the temperature rises above the set point, it turns the heating system off.
How to Choose the Right Room Thermostat.
When selecting a room thermostat, consider the following factors:
Type of Thermostat.
- Mechanical (Analogue) Thermostats – Basic, affordable, but less precise. Best for simple heating systems and good choice for visually impaired or elderly users. (usually hardwired)
- Digital Thermostats – More accurate and easier to read than mechanical ones. (usually battery operated and can be wireless RF)
- Programmable Thermostats – Ideal if you have a fixed daily routine and want to automate temperature settings. (usually battery operated and can be wireless RF)
- Smart Thermostats – Best for energy efficiency, remote control, and learning-based automation. (usually battery operated and can be wireless RF and Wi-Fi)
Compatibility with Your Heating System.
Ensure the thermostat is compatible with your heating system. Your installer should give you choices and confirm compatibility.
Features to Look For.
- Temperature accuracy – Look for one with high precision to avoid frequent temperature fluctuations.
- Wi-Fi or smart control – Allows remote control via apps (useful if you often travel).
- Zoning capability – If you want to control different rooms separately.
- Learning technology – Some smart thermostats learn your habits and adjust accordingly.
- Energy saving features – Helps reduce energy consumption and lower bills. (optimisation, load compensations)
Ease of Installation.
- Wired thermostats – Require professional installation, but are more reliable.
- Wireless (RF) thermostats – Easier to install and offer flexibility in placement.
Cost.
- Basic thermostats – £20-£50
- Programmable thermostats – £50–£150
- Smart thermostats – £150–£300+
Top Brands to Consider.
- Nest (Google) – Smart learning features.
- Salus – Smart learning features.
- Honeywell Home – Basic and smart options.
- Tado – Energy efficiency and zoning.
- Drayton Wiser – Ideal for UK homes with zonal heating.
- Hive (British Gas) – Smart learning features (may require subscription)
Weather Compensation.
Weather compensation is a control strategy that automatically adjusts the flow temperature of the heat pump based on the outdoor temperature.
When it’s cold outside, the system increases the flow temperature to meet the higher heat demand.
When it’s milder, the flow temperature is reduced — avoiding unnecessary energy use.
This adjustment follows a “heating curve” (sometimes called a weather compensation curve).
Why It’s Important?
1. Maximises Heat Pump Efficiency (COP)
A heat pump’s Coefficient of Performance (COP) improves as flow temperature drops.
Every 1°C reduction in flow temperature can increase efficiency by roughly 2–3%.
Without weather compensation, a fixed (high) flow temperature wastes energy when full output isn’t needed.
Example:
If a system always runs at 50°C but only needs 35°C most days, the heat pump runs harder than necessary — costing more and shortening lifespan.
Maintains Stable Indoor Temperatures
Weather compensation provides gentle, continuous heating rather than sharp on/off cycles.
This creates a more even room temperature.
It’s particularly effective with underfloor heating or oversized radiators, where the system runs low and steady.
Reduces Running Costs
Lower flow temperatures mean lower electricity consumption.
Studies and field data show energy savings of 10–20% are typical with proper compensation control.
4. Protects System Components
Fewer compressor starts and smoother load variation extend the lifespan of the heat pump.
Lower return water temperatures also reduce stress on the refrigerant circuit.
5. Supports Compliance & Best Practice
Required under MCS MIS 3005 and BS EN 12831 system design for heat pumps.
Most manufacturers (Mitsubishi, Vaillant, Samsung, etc.) provide built-in weather compensation as standard.
Without it, the system may fail performance testing under SAP 10.2 / SCOP calculations.
How It’s Set Up
A temperature sensor is installed outdoors (away from direct sunlight) and linked to the heat pump controller.
The installer programs a heating curve — e.g.:
45°C flow when it’s 0°C outside
30°C flow when it’s 15°C outside
Fine-tuning is done after a few weeks to match comfort and efficiency.
Common Mistakes
Curve not set up correctly → house runs cold or bills stay high.
Thermostat overrides weather comp → system cycles unnecessarily.
Missing outdoor sensor or disabled feature → system defaults to fixed flow temperature.
In short:
Weather compensation makes a heat pump smarter, cheaper to run, and longer-lasting, by matching heat output to the actual weather.
Balancing.
With our controls in place and the system commissioned, a good heating engineer will always balance the system. This is to make sure the water within our system flows to the furthest part of the system and allows all the radiators to be heat up how they should. Full balancing article here.