diff --git a/server/routes/admin/preview.js b/server/routes/admin/preview.js
index a31a613..df1d94b 100644
--- a/server/routes/admin/preview.js
+++ b/server/routes/admin/preview.js
@@ -13,6 +13,7 @@ import { getRepoInfo } from '../../services/giteaAdmin.js'
 const router = Router()
 router.use(requireAppwriteStaff)
 
+const BUSY = 'Server ausgelastet, versuche es gleich noch mal'
 const MODES = ['auto', 'build', 'dev', 'off']
 const SHA_RE = /^[0-9a-f]{7,40}$/
 
@@ -74,13 +75,17 @@ async function triggerRebuild(doc) {
     branch,
     subdomain: doc.subdomain,
   }
-  return runDeploy(repo, branch, cfg, { project: doc })
+  const result = await runDeploy(repo, branch, cfg, { project: doc })
+  // runDeploy meldet Runner-Fehler im Ergebnis; Schutzschalter (503) an WOMS durchreichen
+  if (result?.error && /Server ausgelastet/.test(result.error)) throw fail(503, BUSY)
+  return result
 }
 
 const wrap = (fn) => async (req, res) => {
   try {
     await fn(req, res)
   } catch (err) {
+    if (!err.expected && err.status === 503) return res.status(503).json({ error: BUSY })
     const status = err.expected ? err.status : 500
     if (!err.expected) console.error('[admin/preview]', err.message)
     res.status(status).json({ error: !err.expected ? 'Preview-Aktion fehlgeschlagen' : err.message })
diff --git a/test/previewAdmin.test.js b/test/previewAdmin.test.js
index 68b041f..32a83f3 100644
--- a/test/previewAdmin.test.js
+++ b/test/previewAdmin.test.js
@@ -11,7 +11,7 @@ import { startFakeAppwrite } from './helpers/fakeAppwrite.js'
 let aw, runner, gitea, app, base, tmp, cfg, envLib, logs
 const key = crypto.randomBytes(32)
 const SHA = 'c'.repeat(40)
-const rs = { calls: [], slow: false, result: 'static' }
+const rs = { calls: [], busy: false, slow: false, result: 'static' }
 
 before(async () => {
   const seed = [
@@ -30,6 +30,7 @@ before(async () => {
     let raw = ''
     req.on('data', (c) => (raw += c))
     req.on('end', () => {
+      if (rs.busy && (req.url === '/jobs/build' || req.url.endsWith('/start'))) { res.statusCode = 503; res.setHeader('Content-Type', 'application/json'); return res.end(JSON.stringify({ error: 'Server ausgelastet' })) }
       rs.calls.push({ method: req.method, url: req.url, body: raw ? JSON.parse(raw) : null })
       res.setHeader('Content-Type', 'application/json')
       if (req.method === 'POST' && req.url === '/jobs/build') return res.end(JSON.stringify({ runId: 'run-x' }))
@@ -87,7 +88,7 @@ after(async () => {
   await fs.rm(tmp, { recursive: true, force: true })
 })
 
-beforeEach(() => { rs.slow = false; rs.result = 'static'; rs.calls = []; cfg.previewRunner.enabled = true; process.env.PREVIEW_ENV_KEY = key.toString('base64') })
+beforeEach(() => { rs.busy = false; rs.slow = false; rs.result = 'static'; rs.calls = []; cfg.previewRunner.enabled = true; process.env.PREVIEW_ENV_KEY = key.toString('base64') })
 
 const call = (method, p, body, jwt = 'jwt-admin') =>
   fetch(`${base}${p}`, {
@@ -273,3 +274,12 @@ test('dev/start ohne gespeicherten Stand: 409; dev/stop ändert failed nicht', a
   const r = await call('POST', '/pns/preview/dev/stop')
   assert.equal((await r.json()).state, 'failed')
 })
+
+test('Runner-Schutzschalter 503: rebuild und dev/start melden Server ausgelastet', async () => {
+  rs.busy = true
+  for (const p of ['/pe/preview/rebuild', '/pw/preview/dev/start']) {
+    const r = await call('POST', p)
+    assert.equal(r.status, 503, p)
+    assert.deepEqual(await r.json(), { error: 'Server ausgelastet, versuche es gleich noch mal' })
+  }
+})