Naboo - How do you solve the error message “A03 boiler safety alarm”?

A03 Boiler safety alarm warn that boiler safety thermostat F3 switch. 
As consequence C6 will open deactivating any function and generating the message.

This message requires the intervention of an authorized technician; causes of the fault must be investigated as per prescriptions.

Description

The boiler expansion PCB get power (230V AC) on inlet 47 and in case of no power supply generate the error message.

Warning

The boiler safety switch open when exceeded boiler limit of 150°C/302°F. 
L’intervento avviene anche nel caso le temperature scendano vicino a 0°C/32°F

Reset

Open front panel and reactivate the thermal safety F3 pressing the reset button.

Checks

Perform following checks: 
- Check current on power lines, must be about 0A - Check C6 contacts; must be open with C6 not powered; in case they stay closed change C6. - Check C4 and C5 (C3 for smaller unit) contacts or SSR stay open when unit is OFF or in standby mode; in case change them. 
- Check boiler status and if limescale exists. - Check status of level probes.

In the event of a serious failure of the boiler system, it is possible to temporarily deactivate the boiler and operate the appliance in direct steam mode by acting from service level – oven model. 
Remember to turn off the water pressure switch.