The Gaggia TS uses a level probe in the water boiler to detect the water level by measuring the conductivity of the water.
The probe is connected to the controller, and there is also a connection to the base of the boiler to form a complete circuit through the boiler and water when the level rises to contact the probe.
If water is not detected by the controller as being in contact with probe, it does not allow the boiler element to switch on.
Over time, scale can build up on the probe, effectively insulating it. In this case, the boiler level may be incorrect (as the water can rise until it is in contact with part of the probe which does not have scale formed on it yet). Over time the level of water will rise in the boiler, and there will be less space for steam.
In the worst case, the water level will not be detected by the controller, and to prevent overfilling, it will stop the fill pump and close the fill solenoid. In this case, the element will not switch on. Note a faulty element, pressurstat, or controller, can also give these symptoms.
To clean the element, remove the orange wire and loosen the smaller lock-nut. The probe can then be withdrawn.
Soak the probe in a small amount of descaler to remove any accumulated calcium carbonate build up.
Re-insert the cleaned probe back through the white insulator and tighten the locknut.
Replace the lid and switch the machine on. Check for steam leaks from the probe area once the boiler is up to pressure. If necessary, switch off and depressurise the boiler (by opening the steam tap) and tighten the probe securing nut.
The following video shows the correct operation of the water level probe.