Device for heat exchange between flowable media

A device for heat exchange between flowable media, at least one of which is in the fluid state, having a heat exchanger block, which is bounded on one side by an inlet chamber (1) and on the opposite side by a outlet chamber (3) for intake and discharge of the fluid medium, having fluid paths (7) for the fluid medium which extend through the block from the inlet chamber (1) to the outlet chamber (3) and which are separated from each other by flow paths positioned between them for conveyance of the other medium capable of flow, and having a cover plate (9), which, covering the fluid paths (7) and flow paths (8), extend from the inlet chamber (1) to the outlet chamber (3), characterized in that the cover plate (9) has at least one interior passage (13) which, bypassing the fluid paths (7), extends as bypass channel from the inlet chamber (1) to the outlet chamber (3), may be blocked by at least one pressure control mechanism (11), and may be unblocked by opening of the mechanism (11) on the basis of a differential pressure exceeding a predetermined threshold value and prevailing between inlet chamber (1) and outlet chamber (3).