The Gaggia TS grouphead is unusual in that it is electrically heated, with an 80W element inside and a thermostat mounted on the top.
Other manufacturers use a group such as the E61, which rely on a thermo-syphon system to keep the head at brew temperature. There is a pipe circuit through the head and boiler forming a loop. Heated water flows around the loop through convection, keeping the group warm.
The TS group only has a single feed of water from the boiler heat-exchanger, and so would not be heated as quickly or efficiently as the E61 with its circulation loop.
The element thermostat is fixed at 103degC, although other values can be substituted to suit the users’s taste.
On the side of the head is the 3-way valve. This provides a route for the pressurised water from above the coffee puck to flow to the drip tray after the shot is completed, so the user is not sprayed with boiling hot coffee under pressure when they remove the portafilter.
Once a week it is recommended to backflush the group head (using Puly Caff or similar), to remove stale coffee residue in the screen, group head, and 3-way valve.