Heating Controls and Thermostats: Getting the Most from Your System

Room thermostats and how they work

A room thermostat measures the air temperature in one location, typically a hallway or living room, and switches the whole heating system on or off (or signals a smart boiler) to keep that area at the set temperature. Because it only measures one room, other rooms may run warmer or cooler depending on their own heat loss and radiator sizing.

Positioning matters: a thermostat placed near a radiator, in direct sunlight, or in a draughty spot will give a misleading reading and cause the whole system to under- or overheat the rest of the house. If yours is in an awkward spot, this is worth mentioning to an engineer, since repositioning or moving to a wireless model can noticeably improve comfort.

TRVs and room-by-room control

TRVs (thermostatic radiator valves) sit on individual radiators and respond to the temperature immediately around them, closing off flow once that room reaches the set level. This allows different rooms to be kept at different temperatures, for example a cooler bedroom and a warmer living room, using the same boiler and pipework.

It is worth noting that the room containing the main thermostat should generally not also have a TRV set restrictively low, since the two controls can end up working against each other, with the thermostat calling for heat that the TRV in that same room then blocks. Many homes leave that one radiator's TRV fully open and let the room thermostat do the main work in that space.

Programmers and timers

A programmer sets when the heating switches on and off through the day, working alongside the thermostat, which then decides whether heat is actually needed once the programmer allows it. A well set programmer avoids heating an empty house during the day and stops well before bedtime, since most homes retain warmth for a while after the heating switches off.

For many households, two shorter heating periods, morning and evening, work better and more efficiently than one long block running through the middle of the day when nobody is home.

Smart thermostats and controls

Smart thermostats add scheduling flexibility, remote control from a phone, and often more sophisticated logic than a basic mechanical timer, such as learning how long a house takes to heat up and adjusting the start time automatically. They can be a genuine improvement for households with irregular schedules, since heating can be adjusted on the move rather than sticking to a fixed timetable.

That said, a smart thermostat is not a substitute for a well-balanced system; if radiators are sludged up or TRVs are seized, a smart control will not fix those underlying issues, it will simply manage a system that is already working properly with more flexibility.

Weather compensation and load compensation

Weather compensation uses an external sensor to adjust the boiler's flow temperature automatically based on the outside temperature, running the boiler gently on mild days and harder on cold ones, rather than always aiming for the same fixed flow temperature regardless of conditions. This tends to produce steadier, more even heat and can improve efficiency.

Load compensation is a related but different approach, where the boiler's controls monitor how quickly the house is heating up and adjust output accordingly, without needing an external sensor. Many modern boilers support one or both of these features, though they need to be enabled and configured correctly during installation or a service visit to take effect.

Boiler flow temperature and condensing efficiency

Modern condensing boilers are most efficient when the flow temperature (the temperature of water leaving the boiler for the radiators) is set relatively low, generally recommended around 60 to 65°C or lower for heating, since this allows the boiler to condense properly and recover extra heat from the flue gases. Many boilers are still left on much higher factory-default flow temperatures, which quietly wastes fuel.

Lowering the flow temperature can mean radiators take slightly longer to reach the target room temperature, so it works best alongside a slightly longer heating period rather than short, hard bursts. An engineer can adjust this setting on the boiler during a service visit and explain what suits your particular radiators and pipework.

Sensible target temperatures

Many households find 18 to 21°C for living areas and slightly cooler for bedrooms, perhaps 16 to 18°C, comfortable and reasonably efficient, though personal preference and household members' needs vary. Turning the heating fully off when out for a short period and then blasting it back up on return is generally less efficient than maintaining a slightly lower background temperature and adjusting the programmer sensibly.

Every degree the thermostat is turned down can make a noticeable difference to running costs over a heating season, so small, sustained adjustments tend to save more money than occasional dramatic changes, while keeping the home comfortable throughout.

Frequently asked questions

Where's the best place to put a room thermostat?

A hallway or a well-used living room, away from radiators, direct sunlight and draughts, generally gives the most representative reading of the home's overall temperature. Kitchens are usually avoided due to heat from cooking affecting the reading.

Should I turn the heating off completely when I'm out?

For short periods, it is often more efficient to leave the heating on a lower background setting than to turn it off entirely and then heat the house from cold, particularly in winter, since reheating from a cold start uses more energy than maintaining a steady lower temperature.

Do smart thermostats actually save money?

They can, mainly by avoiding heating an empty home and by giving more precise scheduling than a basic timer, but savings depend on how the household currently uses its heating. They will not compensate for an inefficient system with sludge build-up or seized TRVs.

What flow temperature should my boiler be set to?

For most condensing combi and system boilers, a flow temperature of around 60 to 65°C for heating is a sensible starting point for good efficiency, though the ideal setting depends on your radiators and how quickly your home heats up. An engineer can help set this correctly during a service.

Why does one room stay cold even with the thermostat turned up?

This is usually a TRV or radiator sizing issue in that specific room rather than a fault with the main thermostat, which only measures the temperature in its own location. Checking that room's TRV is open and the radiator itself is not sludged up is a good first step.