Heating Controls Explained: Thermostat, Timer and TRVs
How room thermostats, programmers, TRVs and smart controls work together in a UK home, and how to set them to stay comfortable without overpaying.
Many people have heating controls that they never quite understood, and they set them once and leave them. Used well, they let you stay comfortable at lower cost, because the boiler is only heating what you actually need. This guide explains the common controls in plain terms so you can get the best from what you already have.
The main parts
Programmer or timer
Tells the heating when to switch on and off, and often hot water as well. It controls the times, not the temperature.
Room thermostat
Measures the temperature in one location, normally the hall or living room, and turns the boiler off when that room reaches your chosen setting. It controls the temperature of one zone.
Thermostatic radiator valves (TRVs)
Fitted to radiator pipes, they adjust how much hot water enters each radiator, based on the temperature around them. Numbers typically run from 1 to 5, with a snowflake for frost protection, and each is about 2 to 3 degrees apart. Setting 3 is often around 18 to 20 degrees.
Boiler thermostat and flow temperature
The boiler has its own setting for the temperature of water leaving it. Condensing boilers are often more efficient when the flow temperature is set lower, but changing this is best done with advice, particularly for hot water in combi systems.
Smart thermostats
These add app control, learning schedules and multi-room zoning. They can be useful if your routine varies, but they do not magically save money by themselves; the savings come from how you use them.
How they work together
- The programmer decides when the heating runs.
- The room thermostat decides whether the boiler fires while it is running.
- The TRVs decide how much each room gets.
This means the room with the thermostat should not have a TRV turned down low, otherwise the system may not reach the temperature it expects, and the boiler will run on. The room thermostat room is normally left with its TRV fully open, or has no TRV.
Sensible settings
| Setting | Typical guidance |
|---|---|
| Room thermostat | Around 18 to 21 degrees in living areas, depending on comfort and health needs |
| Bedrooms | Often cooler, around 16 to 18 degrees |
| Timer | Start 30 to 60 minutes before you need warmth, and finish 30 minutes before bed |
| Unused rooms | TRV low, around 1 or 2, not off, to avoid damp |
| Away | Frost setting around 5 to 10 degrees |
Turning the thermostat higher does not heat the home faster; it just heats for longer.
Common mistakes
- Turning TRVs to 5 to heat faster. They simply heat the room until it reaches the max setting.
- Blocking radiators or thermostats with curtains or sofas, which makes them read wrong.
- Setting the timer for all day on all days when nobody is home.
- Forgetting to adjust the clock after daylight saving changes.
- Closing all TRVs in unused rooms completely, which can cause damp.
Quick wins
- Reduce the room thermostat by one degree. Many households find they barely notice, though savings vary.
- Use a timer to match your real routine.
- Reflect heat from radiators on external walls using foil panels.
- Keep radiators clear of furniture.
- Bleed radiators; see our step-by-step guide.
When to upgrade
If you have no room thermostat, no programmer or no TRVs on most radiators, adding them is generally one of the better value heating upgrades. Costs vary with the system; a plumber or heating engineer can advise. Any work on gas systems must be done by a Gas Safe registered engineer, and electrical wiring for controls by a competent electrician.
Rented homes
You can usually adjust TRVs and timers. If controls are broken or missing, tell your landlord, as heating installations are generally their responsibility. See tenant vs landlord repairs.
You can search for heating engineers on Compito, compare ID-verified providers by postcode and send a request. For wider savings, see energy-saving quick wins.
A worked example
A household has a programmer set to run from 5am to 11pm, a room thermostat at 23 degrees and TRVs at 5 everywhere. The house is hot in some rooms and cool in others, and the boiler runs for long periods. A sensible reset: heating on 30 to 60 minutes before the household wakes and off 30 minutes before bed, thermostat at 19 or 20, living-room TRV open and bedroom TRVs at 2 or 3. The house feels more even, and the boiler is not running to chase an unrealistic target.
Check your system first
Systems differ. A combi boiler heats water on demand and may have no cylinder timer. A system or regular boiler with a cylinder usually has separate hot water and heating times. Underfloor heating often uses its own thermostats. Look at the manuals or ask an engineer if you are unsure before changing settings.
Weather compensation and smart features
Some controls adjust flow temperature based on the weather outside, or learn how quickly your home heats. These can improve efficiency when set up properly. They are no replacement for good insulation and sensible schedules.
Bleed, balance and service
Controls work best when the system is in good order. Bleed trapped air from radiators, and ask an engineer to balance the system if some radiators stay cooler than others. An annual service keeps the boiler efficient; see boiler service: what to expect.
Safety notes
Never disable safety devices or tamper with boiler controls beyond the user settings. If you notice odd noises, leaks or a smell of gas, stop and call a Gas Safe registered engineer; in a gas emergency call the National Gas Emergency Service. Keep a working carbon monoxide alarm; see carbon monoxide alarm guide.
Frequently asked questions
Should I turn the heating off when I go out?
For several hours, yes, or reduce it with the timer. Well-insulated homes lose heat slowly, so short outings make little difference either way.
What number should TRVs be set to?
Around 3 suits many living rooms, with 2 for bedrooms. Adjust to comfort.
Do smart thermostats save money?
They can, if they help you heat only when needed. Savings depend on your habits and home.