Honeywell Gas control unit 0640520

The Honeywell Gas control unit 0640520 is a control box for two-stage forced draught burners, suitable for gas or oil fuel. It manages the burner sequence with a waiting time of 9 s, pre-purge time of 24 s, pre-ignition time of 3 s, and safety time of 3 s. The unit operates on a supply voltage of 220–240 V, consumes 10 W, and has an amplifier sensitivity of 1 µA with a minimum current from the UV tube or ionisation probe of 5 µA. It weighs 0.35 kg net, has protection class IP44, and is certified to EN 298 and CE. This control box fits the Honeywell MMG811.1 mod.33.

Parts of this type are selected by matching the supply voltage, safety time, and flame detector compatibility. The control box must be installed in any position, but the wiring base must be correctly connected. Before ordering, verify the burner's fuel type, stage count, and forced draught configuration. The unit's dimensions and mounting holes should be compared with the existing control box.

Common failures include the burner not starting, repeated lockouts, or the flame signal not being detected. Check the flame detector cable for damage, ensure the air proving switch operates within 6 s, and verify the supply voltage is within the specified range. If the control box fails, the burner may shut down and require a manual reset.