No coffee today due to a Gaggia TS fault. The red neon on the front panel is permanently lit (usually meaning the water tank is empty). Unfortunately for me it is completely full.
I even tried a pinch of salt in the water to see if it would increase the conductivity and also removing one of the metal strips in the tank and holding it in contact with the other to see if that fooled the controller into thinking there was plenty of water. No luck.
Next thing to check is the wiring. Hoping for a fault here, as a break in the wires from the sensing plates to the controller could save some expense. Sadly these were fine also.
Only thing left was to replace the controller which is low down on the right hand side.
Once unbolted, the connections can be numbered for easy relocation to the replacement controller.
The connections to the tank level probes are on pin 10 (earth to the boiler and to one of the tank probes), and 8 (to the other tank probe). Connection 9 is to the boiler probe.
The new controller is a Giemme RL0 1E/1S/4C/F (also coded as 01.03.0036).
Once in, everything was back to normal.
In case you need to check your own controller, the video below shows how it should work.