A double valve, suitable in particular for circulation heating with a heating boiler and a separate boiler circuit and heating circuit, to which can be fed two liquid flows of this circuit, at different temperatures, for mixing, contains an expanding material body to adjust a valve shaft supporting the two valve bodies. By means of this valve shaft, the valve bodies can be adjusted by the expanding material body as a function of its temperature, such that the boiler circuit remains inherently sealed until the water to be emitted into the heating circuit has reached a specific nominal temperature. The heating circuit is not connected directly into the boiler circuit until then. IMAGE
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