De Dietrich 83758940 draught thermostat 85C

A draught thermostat is a mechanical safety device that monitors the temperature in the flue gas path of a boiler or burner system. When the flue temperature exceeds or falls below a preset switching point, the thermostat opens or closes a contact, which can interrupt the burner control sequence or trigger an alarm. Parts of this type are typically mounted on the flue gas outlet or the draught diverter, and they act directly on the control circuit without relying on a control board. The switching point, here indicated as 85°C, determines at which temperature the contact changes state – a critical parameter for ensuring safe operation and preventing damage from overheating or insufficient draught. When selecting a replacement for a draught thermostat, confirm the switching temperature and the reset type: some thermostats reset automatically once the temperature returns to normal, while others require a manual reset, which adds a layer of safety by forcing an inspection after a fault. The connection terminals and mounting method must also match the original installation, as the probe form and cable length vary between models. A typical failure of such thermostats is a drift in the switching point, causing the device to trip too early or not at all, or mechanical wear that prevents proper contact closure. Check the switching action visually with a multimeter before fitting. For a De Dietrich 83758940 draught thermostat, the catalogue number is 336.805.015. This is a direct-acting mechanical device rated at 85°C. Ensure the flue gas temperature in the application does not consistently exceed or linger near that point, or nuisance tripping may occur. Always compare the physical dimensions and electrical ratings with the part being replaced.