Check the thermometer

Compare it with a probe

Weber UK: the lid thermometer reads the air under the dome; for accurate low and slow cooking use a probe near the food. Weber gives no check or adjustment for the dial; the boiling-water check below is general practice.

1. Light a medium indirect fire and let it settle.
2. Clip a thermometer's air probe at grate level, near the middle.
3. After 15 minutes, compare the probe with the dial.
4. Expect a difference: the dome is not the grate. Cook to the probe.
5. If the dial looks wrong even cold, take it out and stand its stem in boiling water: 100 °C at sea level, a little less higher up.
6. If it sticks, fogs or is far out, replace it.