diff --git a/.changeset/preserve-unchanged-settings.md b/.changeset/preserve-unchanged-settings.md
new file mode 100644
index 00000000..3166fb79
--- /dev/null
+++ b/.changeset/preserve-unchanged-settings.md
@@ -0,0 +1,8 @@
+---
+"ftw": patch
+---
+
+Keep unchanged form defaults out of saved settings. Opening Planner and saving
+now preserves an unset SoC limit, including when saving from another tab.
+Show the planner's 95% default maximum instead of 90%.
+Keep an untouched driver profile absent when its choices arrive after the form.
diff --git a/web/settings-shell.test.mjs b/web/settings-shell.test.mjs
index 1a4b8c6e..d231c39d 100644
--- a/web/settings-shell.test.mjs
+++ b/web/settings-shell.test.mjs
@@ -39,6 +39,7 @@ function loadShell(saveResponse, ok = true) {
   for (const id of ELEMENT_IDS) elements[id] = stubElement();
 
   const requests = [];
+  const responses = {};
   const sandbox = {
     window: { FTWSettings: { tabs: {} } },
     document: {
@@ -47,7 +48,7 @@ function loadShell(saveResponse, ok = true) {
     },
     fetch(path, opts) {
       requests.push({ path, opts });
-      return Promise.resolve({ ok, status: ok ? 200 : 400, json: () => Promise.resolve(saveResponse) });
+      return Promise.resolve({ ok, status: ok ? 200 : 400, headers: { get: () => '"config-7"' }, json: () => Promise.resolve(responses[path] ?? saveResponse) });
     },
     // The shell only uses timers to clear the "Saved" status and to poll after
     // a restart; neither is what these tests are about.
@@ -57,12 +58,137 @@ function loadShell(saveResponse, ok = true) {
   sandbox.globalThis = sandbox;
   vm.createContext(sandbox);
   vm.runInContext(source, sandbox);
-  return { elements, requests, tabs: sandbox.window.FTWSettings.tabs };
+  return { elements, requests, responses, tabs: sandbox.window.FTWSettings.tabs,
+    loadTab: file => vm.runInContext(readFileSync(new URL(file, import.meta.url), "utf8"), sandbox) };
 }
 
 // One turn of the event loop, which is all the save chain needs to settle.
 const settled = () => new Promise((resolve) => setImmediate(resolve));
 
+async function formShell(original = { site: { name: "Home" }, planner: { enabled: true }, hidden: { keep: 17 } }) {
+  const rig = loadShell(structuredClone(original));
+  const field = (path, type, value) => Object.assign(stubElement(), { dataset: { path }, type, value });
+  const fields = {
+    min: field("planner.soc_min", "number", "0.1"),
+    max: field("planner.soc_max", "number", "0.95"),
+    engine: field("planner.engine", "select-one", ""),
+    checkbox: Object.assign(stubElement(), { dataset: { checkboxPath: "optional.enabled" }, checked: false }),
+    name: field("site.name", "text", "Home"),
+  };
+  let visible = [], context;
+  rig.elements["settings-body"].querySelectorAll = selector => visible.filter(input =>
+    selector === "[data-path]" ? input.dataset.path : selector === "[data-checkbox-path]" && input.dataset.checkboxPath);
+  rig.tabs.control = { render: ctx => { context = ctx; visible = [fields.name]; return ""; } };
+  rig.tabs.planner = { render: () => { visible = [fields.min, fields.max, fields.engine, fields.checkbox]; return ""; } };
+  rig.elements["settings-btn"].handlers.click();
+  await settled();
+  return { ...rig, original, fields, context, addField: input => visible.push(input), saved: () => JSON.parse(rig.requests.filter(r => r.opts?.method === "POST").at(-1).opts.body) };
+}
+
+describe("unchanged settings fields", () => {
+  for (const visitPlanner of [false, true]) {
+    it("preserves absent values on save, visit Planner=" + visitPlanner, async () => {
+      const rig = await formShell();
+      if (visitPlanner) rig.context.navigateTab("planner");
+      await rig.context.saveConfig();
+      assert.deepEqual(rig.saved(), rig.original);
+      assert.equal(rig.requests.at(-1).opts.headers["If-Match"], '"config-7"');
+    });
+  }
+
+  it("keeps Planner defaults absent after visiting it and saving another tab", async () => {
+    const rig = await formShell();
+    rig.context.navigateTab("planner");
+    rig.context.navigateTab("control");
+    rig.fields.name.value = "New name";
+    await rig.context.saveConfig();
+    assert.deepEqual(rig.saved(), { ...rig.original, site: { name: "New name" } });
+  });
+
+  it("saves explicit number, select and checkbox edits and a later return to the rendered value", async () => {
+    const rig = await formShell();
+    rig.context.navigateTab("planner");
+    rig.fields.max.value = "0.8";
+    rig.fields.engine.value = "core";
+    rig.fields.checkbox.checked = true;
+    await rig.context.saveConfig();
+    assert.deepEqual(rig.saved().planner, { enabled: true, soc_max: 0.8, engine: "core" });
+    assert.deepEqual(rig.saved().optional, { enabled: true });
+    rig.fields.max.value = "0.95";
+    await rig.context.saveConfig();
+    assert.equal(rig.saved().planner.soc_max, 0.95);
+  });
+
+  it("preserves a late secret input until its value changes", async () => {
+    const rig = await formShell();
+    const secret = Object.assign(stubElement(), { dataset: { path: "device.secret" }, type: "password", defaultValue: "", value: "" });
+    rig.addField(secret);
+    await rig.context.saveConfig();
+    assert.deepEqual(rig.saved(), rig.original);
+    secret.value = "local-test-value";
+    await rig.context.saveConfig();
+    assert.equal(rig.saved().device.secret, "local-test-value");
+  });
+});
+
+// Run the real asynchronous Devices catalog callback. The shim parses the
+// select it inserts; like HTMLSelectElement, it has no defaultValue property.
+async function profileShell() {
+  const original = { site: { name: "Home" }, drivers: [{ name: "GoodWe", lua: "drivers/goodwe.lua",
+    capabilities: { modbus: { unit_id: 1 } }, config: {} }] };
+  const rig = await formShell(original);
+  rig.loadTab("./settings/tabs/devices.js");
+  rig.responses["/api/drivers/catalog"] = { entries: [{ id: "goodwe", path: "drivers/goodwe.lua", version: "1.0.2" }] };
+  const unit = Object.assign(stubElement(), { dataset: { path: "drivers.0.capabilities.modbus.unit_id" },
+    type: "number", defaultValue: "1", value: "1" });
+  rig.addField(unit);
+  let select;
+  const slot = {
+    getAttribute: () => "0",
+    set innerHTML(html) {
+      const options = [...html.matchAll(/<option value="([^"]*)"([^>]*)>/g)]
+        .map(([, value, attrs]) => ({ value, defaultSelected: /\bselected\b/.test(attrs) }));
+      select = Object.assign(stubElement(), { type: "select-one", options,
+        dataset: { path: html.match(/data-path="([^"]*)"/)[1] },
+        value: (options.find(option => option.defaultSelected) || options[0]).value });
+      rig.addField(select);
+    },
+    querySelector: () => select,
+  };
+  const body = rig.elements["settings-body"];
+  const fields = body.querySelectorAll;
+  body.querySelectorAll = selector => selector === ".drv-profile-slot" ? [slot] : fields(selector);
+  body.querySelector = selector => selector === '[data-path="drivers.0.capabilities.modbus.unit_id"]' ? unit : null;
+  rig.tabs.devices.after({ ...rig.context, escHtml: String, help: () => "" });
+  assert.equal(select, undefined, "the catalog has not arrived during render");
+  await settled();
+  assert.equal("defaultValue" in select, false);
+  return { ...rig, select, unit };
+}
+
+describe("late driver profile fields", () => {
+  for (const switchTab of [false, true]) {
+    it("keeps an untouched profile absent, switch tab=" + switchTab, async () => {
+      const rig = await profileShell();
+      if (switchTab) rig.context.navigateTab("control");
+      await rig.context.saveConfig();
+      assert.deepEqual(rig.saved(), rig.original);
+    });
+  }
+
+  it("saves an explicit profile and its programmatic Unit ID, including a later return", async () => {
+    const rig = await profileShell();
+    for (const [profile, unitID] of [["gw8kn-et-hk3000", 247], ["community-v1", 1]]) {
+      rig.select.value = profile;
+      rig.select.handlers.change();
+      assert.equal(rig.unit.value, String(unitID));
+      await rig.context.saveConfig();
+      assert.deepEqual(rig.saved().drivers[0], { ...rig.original.drivers[0],
+        capabilities: { modbus: { unit_id: unitID } }, config: { profile } });
+    }
+  });
+});
+
 describe("the settings shell after a save", () => {
   it("calls the tab back so it can ask the box again", async () => {
     const { elements, tabs } = loadShell({ restart_required: false, restart_reasons: [] });
diff --git a/web/settings.js b/web/settings.js
index 5692db81..9501edc0 100644
--- a/web/settings.js
+++ b/web/settings.js
@@ -18,7 +18,7 @@
 //
 // ctx is built fresh on each render and exposes the shell's helpers
 // (field, selectField, help, escHtml, getByPath, setByPath,
-// captureCurrentTab, renderTab, bodyEl, config).
+// captureCurrentTab, rememberFieldValue, renderTab, bodyEl, config).
 (function () {
   "use strict";
 
@@ -44,6 +44,7 @@
   var currentConfig = null;
   var configETag = null;
   var currentTab = "control";
+  var fieldValues = new WeakMap();
 
   openBtn.addEventListener("click", function () {
     apiFetch("/api/config")
@@ -220,9 +221,21 @@
     statusEl.className = "settings-status" + (kind ? " " + kind : "");
   }
 
+  // Async tabs register a field when they insert it, before the user can edit it.
+  function rememberFieldValue(input) {
+    fieldValues.set(input, input.dataset.checkboxPath ? input.checked : input.value);
+  }
+
+  function fieldValue(input, defaultValue) {
+    // Late inputs can also use their DOM default; selects have no defaultValue.
+    return fieldValues.has(input) ? fieldValues.get(input) : defaultValue;
+  }
+
   function captureCurrentTab() {
     var inputs = bodyEl.querySelectorAll("[data-path]");
     inputs.forEach(function (input) {
+      // A displayed default must not become a saved setting on an unchanged form.
+      if (fieldValue(input, input.defaultValue) === input.value) return;
       var path = input.dataset.path;
       var val = input.type === "number" ? parseFloat(input.value) : input.value;
       if (input.type === "number" && isNaN(val)) val = 0;
@@ -232,9 +245,12 @@
       // Preserve a stored password when the user hasn't typed over it.
       if (input.type === "password" && val === "" && getByPath(currentConfig, path, "")) return;
       setByPath(currentConfig, path, val);
+      fieldValues.set(input, input.value);
     });
     bodyEl.querySelectorAll("[data-checkbox-path]").forEach(function (input) {
+      if (fieldValue(input, input.defaultChecked) === input.checked) return;
       setByPath(currentConfig, input.dataset.checkboxPath, input.checked);
+      fieldValues.set(input, input.checked);
     });
   }
 
@@ -301,6 +317,7 @@
       getByPath: getByPath,
       setByPath: setByPath,
       captureCurrentTab: captureCurrentTab,
+      rememberFieldValue: rememberFieldValue,
       renderTab: renderTab,
       navigateTab: navigateTab,
       saveConfig: saveSettings,
@@ -314,9 +331,11 @@
       console.error("tab render:", tab, e);
     }
     bodyEl.innerHTML = html;
+    bodyEl.querySelectorAll("[data-path]").forEach(rememberFieldValue);
 
     // Generic handler for data-checkbox-path — shared across every tab.
     bodyEl.querySelectorAll("[data-checkbox-path]").forEach(function (cb) {
+      rememberFieldValue(cb);
       cb.addEventListener("change", function () {
         setByPath(currentConfig, cb.dataset.checkboxPath, cb.checked);
       });
diff --git a/web/settings/tabs/devices.js b/web/settings/tabs/devices.js
index 7d96a051..c2038696 100644
--- a/web/settings/tabs/devices.js
+++ b/web/settings/tabs/devices.js
@@ -1537,6 +1537,7 @@
           fs += '</select></fieldset>';
           slot.innerHTML = fs;
           var select = slot.querySelector(".drv-profile-select");
+          if (select) ctx.rememberFieldValue(select);
           if (select) select.addEventListener("change", function () {
             var selected = profileByValue(profiles, select.value);
             var unitInput = bodyEl.querySelector('[data-path="drivers.' + dIdx + '.capabilities.modbus.unit_id"]');
diff --git a/web/settings/tabs/planner.js b/web/settings/tabs/planner.js
index b63efed2..2dc009b5 100644
--- a/web/settings/tabs/planner.js
+++ b/web/settings/tabs/planner.js
@@ -66,8 +66,7 @@
   S.tabs.planner = {
     render: function (ctx) {
       var field = ctx.field, selectField = ctx.selectField, help = ctx.help, config = ctx.config;
-      if (!config.planner) config.planner = {};
-      var planner = config.planner;
+      var planner = config.planner || {};
       if (planner.soc_min == null && planner.soc_min_pct != null) {
         planner.soc_min = planner.soc_min_pct / 100;
       }
@@ -86,14 +85,14 @@
           '<div id="planner-hedge-line" style="display:none;color:var(--text-dim);font-size:0.8rem;margin-top:4px"></div>';
       }
       return '<fieldset><legend>MPC Planner</legend>' +
-        '<label><input type="checkbox" data-checkbox-path="planner.enabled"' + (config.planner.enabled ? ' checked' : '') + '> Enabled ' +
+        '<label><input type="checkbox" data-checkbox-path="planner.enabled"' + (planner.enabled ? ' checked' : '') + '> Enabled ' +
         help('Enable the MPC planner. When active it overrides manual mode with an optimised schedule.') + '</label>' +
         '<div class="field-row"><div>' +
         field("House reserve (min SoC, 0–1)", "planner.soc_min", "number", 0.10,
           "Lowest SoC the planner will discharge to, so the house keeps a reserve. 0.10 = 10%.") +
         '</div><div>' +
-        field("Max SoC (0–1)", "planner.soc_max", "number", 0.90,
-          "Highest SoC the planner will charge to. 0.90 = 90%.") +
+        field("Max SoC (0–1)", "planner.soc_max", "number", 0.95,
+          "Highest SoC the planner will charge to. The default is 0.95 = 95%.") +
         '</div></div>' +
         '</fieldset>' +
         '<details class="engine-details">' +
diff --git a/web/settings/tabs/planner.test.mjs b/web/settings/tabs/planner.test.mjs
index 677c57f3..f645a81f 100644
--- a/web/settings/tabs/planner.test.mjs
+++ b/web/settings/tabs/planner.test.mjs
@@ -136,6 +136,17 @@ describe("render", () => {
     assert.ok(!html.includes("planner.soc_max_pct"));
   });
 
+  it("shows Core's default bounds without adding a planner config", () => {
+    const ctx = stubCtx();
+    ctx.config = {};
+    const defaults = {};
+    ctx.field = (label, path, type, value) => { defaults[path] = value; return ""; };
+    tab.render(ctx);
+    assert.equal(defaults["planner.soc_min"], 0.1);
+    assert.equal(defaults["planner.soc_max"], 0.95);
+    assert.deepEqual(ctx.config, {});
+  });
+
   it("promotes legacy soc_min_pct / soc_max_pct into 0–1 fields", () => {
     const ctx = stubCtx();
     ctx.config.planner = { soc_min_pct: 10, soc_max_pct: 90 };