Part of a complex that catalyzes the reversible reduction of CoM-S-S-CoB to the thiol-coenzymes H-S-CoM (coenzyme M) and H-S-CoB (coenzyme B). coenzyme B + coenzyme M + 2 H(+) + 2 reduced [2Fe-2S]-[ferredoxin] = coenzyme M-coenzyme B heterodisulfide + 2 H2 + 2 oxidized [2Fe-2S]-[ferredoxin] Binds 2 [4Fe-4S] clusters per subunit. Cofactor metabolism; coenzyme M-coenzyme B heterodisulfide reduction; coenzyme B and coenzyme M from coenzyme M-coenzyme B heterodisulfide: step 1/1. The heterodisulfide reductase is composed of three subunits; HdrA, HdrB and HdrC. It forms a complex with the F420-non-reducing hydrogenase (Mvh), which provides the reducing equivalents to the heterodisulfide reductase. Belongs to the HdrC family.