TRV Settings Explained: What the Numbers on a Radiator Valve Mean
What a thermostatic radiator valve (TRV) does, what the numbers 1 to 5 and the snowflake mean, which setting to use in each room, and why turning it to 5 won't heat a room faster.
The numbers on a thermostatic radiator valve (TRV) set the room temperature at which the valve closes, not how hot the radiator gets. On most heads, the snowflake or star is frost protection, 1 is cool, 3 is around a comfortable 20°C and 5 is fully open. The exact temperatures vary by make. Setting 3 suits most living rooms, 2 to 3 suits bedrooms, and turning a TRV up to 5 won't heat a cold room any faster. It only lets the room get hotter before the valve shuts.
Key Takeaways
- A TRV senses the air around it and closes when the room reaches the level you set. The number is a target, not a power setting.
- Roughly: snowflake is frost protection, 1 is cool, 3 is about 20°C, 5 is fully open. Check your valve maker's chart for exact figures.
- Setting 3 suits most living rooms. Bedrooms are usually comfortable on 2 or 3, and a rarely used room can sit on 1 or the snowflake.
- Leave the TRV fully open, or fit a plain valve, on the radiator in the room with your main wall thermostat, or the two controls fight each other.
- If a radiator stays cold whatever number you choose, the pin may be stuck, the radiator may need bleeding, or the system may need balancing.
The numbers on a thermostatic radiator valve (TRV) set the room temperature at which the valve closes. They don't control how hot the radiator itself gets. On most TRV heads the snowflake is frost protection, 1 is cool, 3 is around a comfortable 20°C and 5 is fully open, though the exact figures vary by manufacturer. Setting 3 suits most living rooms and 2 to 3 suits bedrooms. Turning a TRV up to 5 won't heat a cold room faster. It just lets the room get hotter before the valve shuts off. With the heating going back on for autumn, this guide explains how to set each radiator properly and what it means when a TRV makes no difference.
What a TRV does
A TRV is the valve with a numbered head, usually on one end of the radiator. Inside the head is a capsule of wax, liquid or gas that expands as the room warms up. As it expands it pushes a pin down into the valve body, which reduces the flow of hot water into the radiator. When the room cools, the capsule contracts, the pin springs back up and hot water flows again.
So a TRV is a small thermostat for one room. It isn't a tap that makes the radiator hotter or cooler. The water reaching the radiator is the same temperature whatever number you pick. What changes is the point at which the valve starts to close.
At the other end of the radiator there's usually a second valve with a plain cap. That's the lockshield, which is set once when the system is balanced and then left alone. If you're not sure which is which, our guide to what a lockshield valve is shows the difference.
What the numbers mean
Most TRV heads use a scale from 0 or the snowflake up to 5, sometimes with small dots between the numbers. The temperatures below are typical, not exact. Each manufacturer publishes its own chart, and the reading depends on where the head sits in the room.
| Setting | Roughly | What it's for |
|---|---|---|
| 0 / off | Closed | Not every head has a true off. Where it does, the radiator stays cold |
| Snowflake / star | About 5 to 8°C | Frost protection for empty rooms in winter |
| 1 | About 10 to 14°C | Unused rooms, hallways, storage |
| 2 | About 15 to 17°C | Bedrooms, landings |
| 3 | About 19 to 21°C | Living rooms, kitchens, home offices |
| 4 | About 22 to 24°C | Bathrooms, rooms for someone who feels the cold |
| 5 / max | About 25°C and above, or fully open | Rarely needed. Useful in summer to rest the pin |
If you want to know what your own valves do, put a cheap room thermometer at sitting height, away from the radiator, and see where the room settles on each number over an evening.
Best setting for each room
- Living room: start on 3. If it feels cool after a couple of hours, go up half a step, not straight to 5.
- Bedrooms: 2 to 3. Most people sleep better in a slightly cooler room.
- Bathroom: 3 to 4, as you're there with wet skin. If you have a heated towel rail on the same circuit, see our guide to a towel rail not heating up if it stays cold.
- Hallway and landing: 2. These spaces take heat from the rest of the house, so they rarely need much of their own.
- Spare rooms: 1 or the snowflake, with the door closed. Don't turn them fully off in a cold spell, as a very cold room makes condensation and mould more likely.
Older people, babies and anyone with a health condition may need rooms kept warmer. Public health advice for cold weather is to heat the rooms you use to at least 18°C.
TRVs and your room thermostat
Most homes have a main room thermostat on a wall, or a smart thermostat, as well as TRVs. The room thermostat tells the boiler when to fire. The TRVs then share out the heat room by room.
The radiator in the same room as the main thermostat shouldn't have its own TRV turned down. If it does, that TRV closes first, the room thermostat never reaches its target, and the boiler keeps running to heat the rest of the house. The usual advice is to leave that radiator's TRV fully open, or have a plain valve fitted instead. Set the room temperature on the wall thermostat and use the TRVs to trim the other rooms. Our guide to how room thermostats work explains where the wall thermostat should go and how to test it.
If you're thinking of room-by-room control from your phone, smart TRV heads replace the numbered head on most modern valve bodies. Our smart thermostat installation and heating controls pages cover what's involved.
Common TRV mistakes
- Turning it to 5 to warm up faster. The valve is already open when the room is cold. All 5 does is overshoot, and it usually gets left there.
- Blocking the head. Curtains, sofas and radiator covers trap warm air around the head, so it closes early and the room stays cool.
- Closing every TRV at once. On some older systems, if every valve shuts and there's no bypass, the boiler can overheat or make a noise. Keep at least one radiator open, usually the one near the room thermostat.
- Leaving them closed all summer. The pin can seize in the down position. Turn them fully open when the heating goes off for the season.
- Adjusting the lockshield instead. The plain-capped valve is for balancing. Turning it by mistake can leave a radiator lukewarm.
When the setting makes no difference
If a radiator stays cold on every number, or stays hot even on 1, the setting isn't the problem. The usual causes are:
| What you notice | Likely cause | Where to start |
|---|---|---|
| Cold on every setting | Pin stuck down | Freeing a stuck TRV pin |
| Hot even on 1 | Pin stuck up, or the head has failed | Check the pin, then replace the head |
| Cold at the top, warm at the bottom | Air in the radiator | How to bleed a radiator |
| Warm at the top, cold at the bottom | Sludge | Radiator not heating up |
| Near radiators hot, far ones lukewarm | System out of balance | How to balance radiators |
| Water round the valve | Worn gland seal or loose joint | Leaking radiator |
A TRV head that's cracked, won't click through its numbers or turns without moving the pin is worn out. Heads can often be replaced without draining the system, but only if the new head fits the existing valve body. If the body itself is corroded or leaking, the radiator needs to be isolated or the system partly drained to change it.
When to call a heating engineer
Call us if a TRV won't free up, a valve is leaking, you want old valves replaced with new TRVs, or several radiators are behaving oddly at once and you can't find a pattern. We cover TRV repair and replacement, radiator repairs and wider central heating faults across London. Our labour is £95 an hour, the £60 call-out is waived when the job runs over 2 hours, and we confirm the price before any work starts.
Radiator ignoring its valve?
Tell us which radiators are affected and whether they stay hot or cold. We'll confirm the price before starting.
📞 Call 020 7870 3200Or see our TRV repairs and pricing.
Frequently Asked Questions
What number should my radiator valve be on?
For most living rooms, 3 is a good starting point, which on most valves is around 20°C. Bedrooms are usually comfortable on 2 or 3, and a spare room you rarely use can sit on 1 or the frost setting. Adjust by one number at a time and give the room a few hours to settle before changing it again.
What temperature is number 3 on a TRV?
On most TRV heads, 3 is roughly 20°C, but it varies between manufacturers and with where the valve sits. A head in a draught or behind a curtain reads the room differently. If you want to know exactly, put a room thermometer at sitting height and see where the room settles on each number.
Does turning a TRV up to 5 heat the room faster?
No. Below its set point a TRV is open, whatever the number, so the radiator heats at the same rate. A higher number only means the room gets hotter before the valve closes. Setting 5 and forgetting to turn it back down is one of the most common ways heating bills creep up.
What does the snowflake on a radiator valve mean?
The snowflake or star is the frost protection setting. The valve stays closed unless the room gets very cold, typically somewhere around 5 to 8°C depending on the make, and then opens to stop pipes and the radiator freezing. It is useful for unused rooms in winter.
Should I turn TRVs off in summer?
It is usually better to turn them fully open in summer when the heating is off. A TRV left closed for months holds its pin down, and the pin is more likely to stick. Turn the heads to the top setting in spring, then set them back to your usual numbers when the heating goes on in autumn.
Sources and further reading
Source links checked 27 September 2026. Scheme rules and manufacturer instructions can change; use the current official guidance for your account or exact appliance.