The first useful distinction is whether the machine is completely cold or only the steam side has stopped heating. Write that down before ordering a heating element.
A machine can light its display while a boiler remains cold. The Linea PB manual gives separate messages for filling, a missing temperature-probe signal, overheating and failure to reach temperature. They call for different investigations.
Start with the affected system
On a machine with separate brew and steam boilers, tell the technician which side still works. Include the exact display wording and when it appeared. A photograph of the normal screen is useful; opening a panel to photograph wiring is not an operator check.
Also report a recent water interruption or a change to the filter supply. The Linea PB filling-failure message means the controller did not receive a full signal in the allowed time. Its heating message reports failure to reach temperature. Neither message, by itself, proves that the element is the failed part.
The heating circuit has to be checked as a system
The heating element, the controls that switch it and the safety devices all belong in the diagnosis. The technician follows the circuit for the exact model, checks the reported fault and tests the relevant components. A parts order should follow that finding.
La Marzocco’s technician-maintenance list includes wiring condition, boiler safety switches, the autofill probe and valve operation. It does not tell an operator to rank those parts by how commonly they supposedly fail.
If the machine overheated before it went cold, include that sequence in the report. Resetting an internal safety thermostat does not explain why it operated. Do not bypass a safety device or repeatedly restart a machine with an electrical fault.
What staff can do
Use only the normal controls and checks described in the operator manual. Note the switch or displayed operating state, any visible water-supply issue and the message on screen. Do not loosen a fitting to prove that water is reaching the boiler.
Keep covers closed. Electrical testing, opening a boiler and internal resets require trained service personnel. The machine’s shutdown instructions still matter: switching it off is not permission to open a hot, pressurized system.
Before approving repair
Ask which test supports the proposed part and whether the original cause has been addressed. If the diagnosis includes water or scale trouble, keep that finding with the maintenance record.
For a machine under manufacturer warranty, start with the manufacturer’s service channel. For other equipment, send us the model and symptoms so we can confirm the service path and arrange diagnosis.
Source: La Marzocco Linea PB manual, safety and maintenance on PDF pages 13 and 21–24, and the distinct boiler/filling messages on PDF page 135. The examples identify diagnostic branches; they are not reset instructions for other machines.