The steam function has a built-in safety cutoff that automatically stops steam delivery after about three minutes to prevent damage.
If it stops after only a minute, it is often because the cappuccino maker system is dirty and needs cleaning.
To fix it, wait a few minutes for the system to reset before trying the steam function again. If the problem persists, unplug the machine, then remove the cappuccino maker, detach the steam nozzle, and wash all parts with warm water. It is important to check that the two small holes in the nozzle are completely clear.
You should never attempt to override the safety cutoff.