diff --git a/src/vaillant/26.vr_71.tsp b/src/vaillant/26.vr_71.tsp
index 3c6513d7..764552fe 100644
--- a/src/vaillant/26.vr_71.tsp
+++ b/src/vaillant/26.vr_71.tsp
@@ -67,7 +67,9 @@ namespace Vr_71 {
   @inherit(w_1)
   @ext(0x2, 0)
   model Mc1Operation {
-    status: onoff;
+    @values(Values_McStatus)
+    status: UCH;
+
     flowtempdesired: temp1;
 
     @in
@@ -80,7 +82,9 @@ namespace Vr_71 {
   @inherit(w_1)
   @ext(0x2, 1)
   model Mc2Operation {
-    status: onoff;
+    @values(Values_McStatus)
+    status: UCH;
+
     flowtempdesired: temp1;
 
     @in
@@ -93,7 +97,9 @@ namespace Vr_71 {
   @inherit(w_1)
   @ext(0x2, 0x2)
   model Mc3Operation {
-    status: onoff;
+    @values(Values_McStatus)
+    status: UCH;
+
     flowtempdesired: temp1;
 
     @in
@@ -137,6 +143,27 @@ namespace Vr_71 {
     on: 20,
   }
 
+  /**
+   * Mixer-circuit operation status. See issue #620.
+   *
+   * Value 4 is written by the controller in a short daily burst (~5 min) on
+   * otherwise-off circuits — a "keep valve operable" maintenance run
+   * (anti-seize).
+   *
+   * Value 2 occurs on cooling-capable systems while the circuit is cooling
+   * (reported for a VR 71 + VRC 700 driving aroVAIR convectors: flow target
+   * 10 °C at 2 versus 42.5-44 °C at 1). On those systems 1 therefore means
+   * "heating" rather than a generic "on"; the label is kept as `on` because
+   * this field used the shared `onoff` type before, and renaming it would
+   * change the reported state for every existing installation.
+   */
+  enum Values_McStatus {
+    off: 0,
+    on: 1,
+    cooling: 2,
+    keepValveOperable: 4,
+  }
+
   /** included parts */
   union _includes {
     Errors_inc,