A mixing unit for a mixer tap, the mixing unit comprising: - an initial inlet for an initial incoming stream of fluid having an initial temperature (Tf), - a second inlet for a second incoming stream of fluid having a second temperature (Tc) higher than the initial temperature, - mixing means for mixing the initial incoming stream with the second incoming stream to form an outgoing stream of fluid having an outlet temperature (Tm), - an outlet for the outgoing stream, - a valve, which can be moved in translation along a closure axis between a position in which the second inlet is open and a position in which the second inlet is closed, - an actuating element of the valve, which is arranged at least partially at the outlet so as to deform, depending on the outlet temperature, between: ∘ an initial form, to move the valve to the open position, and ∘ a second form, to move the valve to the closed position, in which - the mixing unit comprises a housing duct which connects the outlet to the second inlet extending along the closure axis, - the valve comprises a plunger extending into the housing duct, via which the actuating element actuates the valve; the mixing unit being characterised in that: - the actuating element is made of a shape-memory alloy; - the actuating element closes the housing duct; - the mixing unit comprises a static seal for sealing the housing duct by the actuating element; - the actuating element comprises: ∘ a perimeter portion surrounding the housing duct and through which the actuating element is attached to the housing duct, and ∘ a central portion, which is displaced along the closure axis relative to the perimeter portion, when the actuating element deforms between its initial and second form, the closure being translationally connected to the central portion along the closure axis. - an initial inlet for an initial incoming stream of fluid having an initial temperature (Tf), - a second inlet for a second incoming stream of fluid having a second temperature (Tc) higher than the initial temperature, - mixing means for mixing the initial incoming stream with the second incoming stream to form an outgoing stream of fluid having an outlet temperature (Tm), - an outlet for the outgoing stream, - a valve, which can be moved in translation along a closure axis between a position in which the second inlet is open and a position in which the second inlet is closed, - an actuating element of the valve, which is arranged at least partially at the outlet so as to deform, depending on the outlet temperature, between: ∘ an initial form, to move the valve to the open position, and ∘ a second form, to move the valve to the closed position, ∘ an initial form, to move the valve to the open position, and ∘ a second form, to move the valve to the closed position, - the mixing unit comprises a housing duct which connects the outlet to the second inlet extending along the closure axis, - the valve comprises a plunger extending into the housing duct, via which the actuating element actuates the valve; - the actuating element is made of a shape-memory alloy; - the actuating element closes the housing duct; - the mixing unit comprises a static seal for sealing the housing duct by the actuating element; - the actuating element comprises: ∘ a perimeter portion surrounding the housing duct and through which the actuating element is attached to the housing duct, and ∘ a central portion, which is displaced along the closure axis relative to the perimeter portion, when the actuating element deforms between its initial and second form, the closure being translationally connected to the central portion along the closure axis. ∘ a perimeter portion surrounding the housing duct and through which the actuating element is attached to the housing duct, and ∘ a central portion, which is displaced along the closure axis relative to the perimeter portion, when the actuating element deforms between its initial and second form, the closure being translationally connected to the central portion along the closure axis.