Ferroli 39821523 Optimax HE DMB04 Honeywell S4962V2001U PCB

The Ferroli 39821523 is a printed circuit board used in Ferroli Optimax HE and Optimax HE Plus appliances. It carries the DMB04 board marking and acts as the main control PCB, handling ignition sequencing, fan and pump control, temperature sensing and fault monitoring. The board sits within the boiler's control box assembly and is the component an engineer will normally test first when an appliance shows electrical or sequencing faults.

• The boiler fails to fire and locks out, with no fault code displayed or a code that clears on reset
• The display is blank, flickers or shows erratic readings
• The fan, pump or diverter valve does not run when there is a demand for heat or hot water
• Repeated lockouts occur shortly after resetting the appliance
• The boiler ignores heating or hot water demands entirely

• Confirm the appliance model and GC number against the compatibility list before ordering
• Check that the board marking on the existing PCB reads DMB04, as Ferroli used more than one board across the Optimax range
• Note the boiler serial number and any fault codes, as these help confirm the diagnosis