What do the symbols on radiator valves mean?

By Sam Wood •  Updated: 10/04/21 

Radiator valves can be a strange thing to understand, what do all the symbols mean? And what temperature do the numbers correlate to? Well worry not, we have a simple, easy to understand guide for you below.

Radiator Valve Manufacturer

Different manufacturers use different symbols on their valves, but they are usually very similar and it can be worked out what each one means. For the purpose of this article, I will be using a Danfoss Thermostatic Radiator Valve as that is what was in my house! It turns out they are a really common valve though so this should be a really good place to start from.

Star or Snowflake Symbol

Star Snowflake Symbol
Star Snowflake Symbol

This is commonly a snowflake but looks more like a star on my radiator. This is the symbol for frost protection mode. In this mode, the radiator and pipes will not be allowed to go below roughly 5°C. This is to stop the water from inside from ever freezing, which if it does can lead to burst pipes. For everyday use, this is essentially the “off” position. Your radiator will not be heating the room but will be protected from frost if the temperature ever gets that low.

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1 Symbol

1 Symbol
1 Symbol

This is the lowest heat setting. On different thermostatic valves, this will mean different temperatures. They will however all be similar heat settings. On the Danfoss this represents a room temperature of 12°C.

Obviously, your radiator is not that precise when it comes to heating the room, and it doesn’t know what the actual room temperature is. So all of these are just guides, they can be effected by the size of the room, insulation level and a ton of other factors. Consider this as your radiator on a low heat setting.

2 Symbol

2 Symbol
2 Symbol

Now we are just working our way through the different heat settings. On my Danfoss, this correlates to 16°C.

3 Symbol

3 Symbol
3 Symbol

This correlates to 20°C and is the mid-range setting.

4 Symbol

4 Symbol
4 Symbol

On my valve this represents 24°C.

Max Open Symbol

Max Open Symbol
Max Open Symbol

Now next to the 4 symbol we have a different icon. This represents the radiator in the max heat setting. When the valve is set here it is fully open and is letting the maximum amount of hot water through from your boiler.

Fully Closed

Fully Closed Symbol
Fully Closed Symbol

This represents the radiator in the fully closed position. The valve is fully shut off and there is no water flowing into it. This is used for when to want to perform maintenance on the radiator and remove it from the wall.

This should not be used as the off setting and you should instead use the frost protection mode. You may face some resistance when trying to get the radiator onto this setting. This is normal and is there to prevent you from doing it by accident.

Related Reading

While you are here you may be interested in these other radiator based posts!

Sam Wood

Wood by name, wood by nature. I am a fully qualified, time-served, award-winning joiner with an NVQ Level 3 in Carpentry and Joinery as well as an HNC in Construction. Beyond my joinery qualifications, I have also earned a degree in building surveying. I believe these qualifications make me perfectly positioned to provide expert advice on many different areas of DIY as well as share all of the tips I have picked up in over a decade working on building sites!