When a boiler detects a fault, it "locks out" and displays a fault code. Pressing the reset button clears the lockout and restarts the ignition sequence. Here's how to do it on the most common boiler brands.
Before you reset
Note down the fault code displayed. This tells you (and any engineer) what caused the lockout. Resetting without fixing the underlying cause may just trigger the same lockout again.
Worcester Bosch
Press and hold the reset button (flame icon) for 3 seconds. The button is usually on the front panel, right side. The boiler will attempt to ignite — if it fires up and stabilises, you're good. If it locks out again, call an engineer.
Vaillant
On ecoTEC models: press the reset button (usually a flame with a line through it) for 3 seconds. On older models with a rotary dial, turn the dial to the reset position and hold for 3 seconds.
Baxi
Press the reset button on the front panel. On the 600 and 700 series, it's marked with "R" or a reset symbol. Hold for 3 seconds.
Ideal
On the Logic Max, navigate to the fault screen and select reset. On older Logic models, press the reset button on the front panel.
When NOT to reset
If you smell gas, do not attempt to reset the boiler. Leave the property, turn off the gas at the meter, and call the National Gas Emergency line: 0800 111 999.