diff --git a/src/control/levelBased.js b/src/control/levelBased.js
index aed0e1b..1668cf4 100644
--- a/src/control/levelBased.js
+++ b/src/control/levelBased.js
@@ -253,6 +253,26 @@ async function run(ctx, controlState, direction) {
     `Level-based: level=${level} dir=${direction} armed=${shiftArmed} hold=${shiftHold} pct=${percControl}`
   );
 
+  // We are past every off-gate, so the station is engaged and the computed
+  // demand is meant to drive pumps. If no machine group is registered the
+  // demand has nowhere to go and the pumps stay silent — the signature of a
+  // dropped Port 2 parent↔group registration (e.g. after a partial redeploy
+  // that recreated this node). Warn once until a group reappears so the
+  // failure isn't invisible.
+  const groupCount = machineGroups ? Object.keys(machineGroups).length : 0;
+  if (groupCount === 0) {
+    if (host && !host._warnedNoMachineGroup) {
+      logger?.warn?.(
+        `Level-based control engaged (demand ${percControl.toFixed(1)} %) but no machine group is registered — `
+        + `pumps cannot be driven. The parent↔group registration was likely lost on a partial redeploy; `
+        + `redeploy/restart fully to re-run the Port 2 registration handshake.`
+      );
+      host._warnedNoMachineGroup = true;
+    }
+  } else if (host) {
+    host._warnedNoMachineGroup = false;
+  }
+
   await _applyMachineGroupLevelControl(machineGroups, percControl, logger);
 }
 
diff --git a/src/control/manual.js b/src/control/manual.js
index e86f890..bb39c83 100644
--- a/src/control/manual.js
+++ b/src/control/manual.js
@@ -28,6 +28,18 @@ async function forwardDemand(ctx, demand) {
       }
     }
   }
+
+  // Neither a group nor a direct machine is registered, so the operator's
+  // demand silently goes nowhere. Surface it — the usual cause is a dropped
+  // Port 2 parent↔child registration after a partial redeploy.
+  const noGroups = !machineGroups || Object.keys(machineGroups).length === 0;
+  const noMachines = !machines || Object.keys(machines).length === 0;
+  if (noGroups && noMachines) {
+    logger?.warn?.(
+      `Manual demand ${demand} not forwarded — no machine group or machine is registered to this pumping station. `
+      + `Check the parent↔child Port 2 registration (redeploy/restart fully to restore it).`
+    );
+  }
 }
 
 module.exports = {
diff --git a/test/basic/control-levelBased.basic.test.js b/test/basic/control-levelBased.basic.test.js
index 6c0fc86..96eedaf 100644
--- a/test/basic/control-levelBased.basic.test.js
+++ b/test/basic/control-levelBased.basic.test.js
@@ -182,3 +182,51 @@ test('no valid level → warns and returns without mutating percControl or calli
     assert.equal(g._calls.handleInput.length, 0);
   }
 });
+
+// Regression: a station engaged above startLevel but with no machine group
+// registered (e.g. the Port 2 parent↔group registration was dropped by a
+// partial redeploy) computes a real demand that goes nowhere. The strategy
+// must surface this once, not fail silently. See the 2026-05-27 "PS not
+// reacting to level" trace.
+test('engaged with NO machine group registered → warns once (throttled via host)', async () => {
+  const ctx = makeCtx(3, { levelbased: { holdLevel: 2 } }); // level 3 > startLevel 2 → engaged
+  ctx.machineGroups = {};                                   // registration lost
+  ctx.host = {};
+  const warns = [];
+  ctx.logger.warn = (m) => warns.push(m);
+
+  const state = { percControl: 0 };
+  await levelBased.run(ctx, state);
+
+  assert.ok(state.percControl > 0, 'demand is computed even though there is no group');
+  assert.equal(warns.length, 1, 'warns exactly once');
+  assert.match(warns[0], /no machine group is registered/i);
+  assert.equal(ctx.host._warnedNoMachineGroup, true);
+
+  // Subsequent ticks while still group-less stay quiet (no log spam).
+  await levelBased.run(ctx, state);
+  assert.equal(warns.length, 1, 'throttled: no repeat warning on the next tick');
+});
+
+test('warning re-arms after a group reappears then disappears again', async () => {
+  const ctx = makeCtx(3, { levelbased: { holdLevel: 2 } });
+  ctx.host = {};
+  const warns = [];
+  ctx.logger.warn = (m) => warns.push(m);
+  const state = { percControl: 0 };
+
+  ctx.machineGroups = {};
+  await levelBased.run(ctx, state);
+  assert.equal(warns.length, 1);
+
+  // Group registers again → flag clears, no new warning.
+  ctx.machineGroups = { a: makeGroup('A') };
+  await levelBased.run(ctx, state);
+  assert.equal(warns.length, 1);
+  assert.equal(ctx.host._warnedNoMachineGroup, false);
+
+  // Group lost again → warns once more.
+  ctx.machineGroups = {};
+  await levelBased.run(ctx, state);
+  assert.equal(warns.length, 2, 're-armed after recovery');
+});