Brentford Room Thermostatic Control updated This is an old one! When these types of controls get old they do not relate to the temperature setting on the dial. The bellows inside get tired, so to achieve 20 degrees C, you may find that you are having to set it at 30 degrees C. So I replaced this with a newer version which also has a light on, a visual aid. They light doesn’t always work, it depends on the wiring already in place, but this was on a Heat only (with Hot Water Cylinder), so it had the necessary wiring. Customer happy.