Some have discussed this potential improvement to temperature stability. (Like an impeller approach, or similar.) I connected a potable water, high temperature circulator pump from one grouphead to the adjacent one and insulated the connecting pipes. Basically it constantly circulates (at pretty high speed) the water in the entire boiler-group system to keep a uniform temperature. The closeup photo shows one of the pipes exiting one head at its group cap. I drilled and tapped the caps for pipe fittings. In addition, I disconnected the two remaining groups and connected the outlet of one of them to the inlet of the boiler with the circulator, so it's preheated. This machine has two boilers, so now the first boiler is dedicated to preheating the second. Finally, the banjo tube of one head is lengthened and the element controlled by PID controller with a thermocouple in the boiler thermowell. The result is an amazingly predictable and stable temperature in the puck. Basically what this gets me is the ability to dial in a temperature and simply know that's the temperature hitting the cake. I can postflush for cleaning until the cows come home because the preheating boiler prevents cooling during this flush. Sorry for the stinky pictures but thought some would be interested anyway. I've had this working flawlessly for more than six months now. The pump is only rated to 125 psi (~8.6 bars) but seems to be ok so far. This has not made every shot perfect. I still need to learn to roast better and tamp and/or distribute consistently, but any question on my temperature has been completely eliminated.
Keith
O yeah, those keypads...
