The Nano 7 is designed for batch sizes of between 90 and 120g green beans. Smaller batches won't roast correctly with the default profile and the machine tries to detect them and alert the user. That is why you sometimes get the "heat too fast" message. It is caused by
- Less than approx 90 g of green beans in the roaster
- No beans in the roaster at all, and
- A batch of roasted beans in the roaster.
However, you can also get this message when you have modified the profile. If you make a change to the initial rate of rise of the profile, you must make a corresponding change to the preheat power setting. That is because preheat power, and preheat power only, controls the first 30 to 40 secs of the roast. After that the curve following commences. If preheat power drives your roast significantly above the profile curve then the roaster will never get a chance to follow the curve because the "heat too fast" error will stop the roast.
The default setting for preheat power is 1050 Watts to achieve 110°C at 60 secs. If you need a slower or faster start to the roast, adjust proportionately then collect and examine roast logs. You are looking for the roast starting out on the profile curve, not above or below the curve.
The maximum value for preheat power is 1400, but it is probably wise not to exceed 1200 to allow for variations in room temperature and mains voltage.