De Dietrich 88065564 Basic relay card

A control board of this type is the central electronic component in a modern wall‑hung boiler. It performs the same function that a dedicated burner control (flame safeguard) does in a larger commercial unit: it manages the ignition sequence, enforces the safety times (pre‑purge, ignition, flame proving, lockout on failure), reads signals from sensors and switches, and drives the fan, gas valve, ignition transformer, and circulation pump. On a basic relay card the outputs are switched via electromechanical relays rather than semiconductor devices, which is typical for simpler or older‑style control boards. Such a board is matched exactly to the boiler model. The manufacturer designs the board’s software, relay logic, and connector layout to work with a specific range of boilers. Even within the same brand, a control board from a different series or power class will not fit or will cause safety faults. When replacing a board, the correct part number must be used; a mismatch in safety times or modulation parameters is a safety issue, not merely a performance nuisance. The board communicates with the room thermostat or external controller, the NTC temperature sensors (flow and return), the air pressure switch, the ionisation electrode, and the modulating gas valve or fan. In a wall‑hung boiler, the control board also governs the three‑way valve (if combi) and the pump overrun sequence. Because the board is the logical centre of the boiler, any replacement must be verified against the boiler’s model and serial number to ensure compatibility.