Automatic dishwasher detergent is effective, safe and rinses clean easily. It is also in-expensive and readily available at any restaurant supply, walmart, or grocery store. Try about a teaspoonful, add hot water, stir or shake to mix, let soak for 20 minutes (or overnight), then rinse clear. If the deposits are extra-thick, you may need to repeat the procedure, but if you follow a regular cleaning procedure then the deposits clean off quickly.
I like cascade gel, because it dissolves quickly for faster cleaning. It is also safer than espresso machine cleaners and de-scalers, because some of them will react poorly with the plastic components that are in some thermal dispensers or the flow valves.
This works great at home and in cafe's. The cafe' should follow this procedure nightly, then in a.m. rinse clear with hot water and the thermal dispenser is warmed up and ready for brewing.