Protein build up is quite normal during the brewing process. The element will struggle if there are burnt protein/sugars on the bottom, which is why you may see the unit not hit the target. 

There are two main reasons for for a protein build up: 

1. Low amount of water in the base of the boiler causing scorching due to, wort with too high a sugar content, collecting on the element. Ensure your recipe creator uses the recoverable dead space for the Grainfather units.  
2. Grain matter settling on the element and burning on the element. Ensure your grain crush has a good proportion of course and fine crushes. Also, consider using the overflow filter to help stop grain matter getting in to the bottom the boiler.  

The Grainfather High Performance Cleaner is specifically designed to remove burnt on proteins.

If using another cleaner, use as directed on the cleaner.

1. Fill the boiler up with 7.5 L (1.98 US Gal) of water.
2. Add 30 ml (1 US fl oz) of Grainfather cleaner (if using another cleaner, use as directed on the cleaner instructions); remember to set the temperature to 55°C (131°F).
3. See details under the cleaning section of the Grainfather manual.

Also, don’t be scared to give the bottom and sides a good scrub with a soft bristle brush. If need be you can increase the temperature to 65°C (149°F) and soak for 30 minutes to soften the buildup. It is best to scrape the element every now and then during the boiling process to minimise protein build up. If you don't, you may cause the element to trip or cut out during boiling.