How a TRV works
The head contains wax or liquid that expands as the room warms. It pushes a pin down, closing the valve. As the room cools it shrinks, the pin rises and hot water flows again.
What the numbers mean
- * or frost: only stops freezing.
- 1–2: cool rooms like bedrooms.
- 3: comfortable for most living spaces.
- 4–5: warmer rooms; 5 is near fully open.
Pro tip: Turning to 5 does not heat the room faster — it just lets it get hotter before closing.
Freeing a stuck pin
- Turn the head to fully open (5) and unscrew it.
- You will see a small metal pin.
- Press it gently: it should spring back up.
- If stuck down, wiggle it gently with grips and a little lubricant.
- Refit the head.
Where TRVs should not go
The room with the main heating thermostat should usually not have a TRV, or it may stop the system working properly. Check the system design.
