The A03 alarm appears on MCZ pellet stoves when the temperature of the pellet container is too high. This is a safety alarm.
You should switch off the appliance and wait for it to cool down, then you can switch it on again.
We can advise you to run the hot air blowers at a higher speed, in order to evacuate the heat from the stove more efficiently during its use.
If the alarm goes off again afterwards, it is often necessary to call a technician.