The reason for condensation of the boiler could below temperature of the coolant in return pipe and low temperature of flue gases. Condensate contains water and acids, which can corrode the metal walls of boilers and pipes very quickly. To prevent condensation, we recommend operating the boiler according to the operational manual, monitor the temperature of the coolant in the return pipe so that it does not fall below 55 C, for this purpose a three-pass valve is installed.