diff --git a/include/cantera/equil/vcs_MultiPhaseEquil.h b/include/cantera/equil/vcs_MultiPhaseEquil.h
index 9e48cc1e7..77ffb8c21 100644
--- a/include/cantera/equil/vcs_MultiPhaseEquil.h
+++ b/include/cantera/equil/vcs_MultiPhaseEquil.h
@@ -272,6 +272,7 @@ public:
      *     stdout from the vcs package (Note, you may have to compile with debug
      *     flags to get some printing).
      * @param logLevel  Determines the amount of printing to the output file.
+     * @deprecated Broken and unused. To be removed after Cantera 2.3.
      */
     int determine_PhaseStability(int iph, double& funcStab, int printLvl= 0, int logLevel = -99);
 
diff --git a/include/cantera/equil/vcs_solve.h b/include/cantera/equil/vcs_solve.h
index e3695760a..86046971b 100644
--- a/include/cantera/equil/vcs_solve.h
+++ b/include/cantera/equil/vcs_solve.h
@@ -120,6 +120,7 @@ public:
      */
     int vcs_solve_TP(int print_lvl, int printDetails, int maxit);
 
+    //! @deprecated Broken and unused. To be removed after Cantera 2.3.
     int vcs_PS(VCS_PROB* vprob, int iph, int printLvl, double& feStable);
 
     /*!
@@ -624,6 +625,7 @@ public:
      *   returned.
      * - -1 = Maximum number of iterations is exceeded. Convergence was not
      *   found.
+     * @deprecated Broken and unused. To be removed after Cantera 2.3.
      */
     int vcs_solve_phaseStability(const int iphase, int ifunc, double& funcval, int print_lvl);
 
diff --git a/src/equil/vcs_MultiPhaseEquil.cpp b/src/equil/vcs_MultiPhaseEquil.cpp
index ae99b77f9..b88544ad9 100644
--- a/src/equil/vcs_MultiPhaseEquil.cpp
+++ b/src/equil/vcs_MultiPhaseEquil.cpp
@@ -1131,6 +1131,8 @@ size_t vcs_MultiPhaseEquil::component(size_t m) const
 
 int vcs_MultiPhaseEquil::determine_PhaseStability(int iph, double& funcStab, int printLvl, int loglevel)
 {
+    warn_deprecated("vcs_MultiPhaseEquil::determine_PhaseStability",
+                    "Broken and unused. To be removed after Cantera 2.3.");
     clockWC tickTock;
     m_printLvl = printLvl;
     m_vprob.m_printLvl = printLvl;
diff --git a/src/equil/vcs_solve_phaseStability.cpp b/src/equil/vcs_solve_phaseStability.cpp
index e1565e4f7..a886934a6 100644
--- a/src/equil/vcs_solve_phaseStability.cpp
+++ b/src/equil/vcs_solve_phaseStability.cpp
@@ -16,6 +16,8 @@ namespace Cantera
 
 int VCS_SOLVE::vcs_PS(VCS_PROB* vprob, int iphase, int printLvl, double& feStable)
 {
+    warn_deprecated("VCS_SOLVE::vcs_PS",
+                    "Broken and unused. To be removed after Cantera 2.3.");
     // ifunc determines the problem type
     int ifunc = 0;
 
@@ -106,6 +108,8 @@ int VCS_SOLVE::vcs_solve_phaseStability(const int iph, const int ifunc,
                                         double& funcVal,
                                         int printLvl)
 {
+    warn_deprecated("VCS_SOLVE::vcs_solve_phaseStability",
+                    "Broken and unused. To be removed after Cantera 2.3.");
     double test = -1.0E-10;
     bool usedZeroedSpecies;