Abstract: A burner control for a condensing furnace having a flame proving circuit that incorporates the flame at the burner to be closed and that opens upon absence of a flame to cause a gas valve to close and block the flow of gas to the burner. A short circuit shunting the flame proving circuit includes a probe that projects into the outlet manifold of the condensing furnace. If liquid level in the outlet manifold reaches the probe, a short circuit is closed between the probe and a ground on the manifold. The control to the valve is energized to close the valve in the same manner as if the flame had extinguished at the burner. Upon closing the gas valve, the burner is extinguished.