You just need to leave the unit swiched on and wait for a little time. After the first incorrect attempt the unit locks and you have to wait for 1 minute, two wrong attempts and it's 2 minutes then 4, 8, 16 and 32 minutes with each further incorrect attempt. Any doubts on how to input the code you should refer to the manufacturers handbook which is available online in pif format
Sharpy, April 2008