diff --git a/apps/frontend/src/app/features/sites/site-detail/site-detail.html b/apps/frontend/src/app/features/sites/site-detail/site-detail.html
index e95ac75..9c4a4bc 100644
--- a/apps/frontend/src/app/features/sites/site-detail/site-detail.html
+++ b/apps/frontend/src/app/features/sites/site-detail/site-detail.html
@@ -36,13 +36,18 @@
       <section class="overview">
         <ev-card class="card card--gauge">
           <span class="card__label">Consommation vs capacité</span>
-          <app-consumption-gauge
-            [consumption]="current()?.consumption_kw ?? 0"
-            [capacity]="s.capacity_kw ?? 0"
-          />
-          <span class="card__value">
-            {{ current()?.consumption_kw ?? '-' }} / {{ s.capacity_kw ?? '-' }} kW
-          </span>
+          @let consumption = consumptionKw();
+          @if (consumption !== null) {
+            <app-consumption-gauge [consumption]="consumption" [capacity]="s.capacity_kw ?? 0" />
+            <span class="card__value">
+              {{ consumptionLabel() }} / {{ s.capacity_kw ?? '-' }} kW
+            </span>
+          } @else {
+            <p class="card__unavailable">
+              Consommation indisponible
+              <span class="metric__reason">({{ consumptionReason() }})</span>
+            </p>
+          }
         </ev-card>
 
         <ev-card class="metrics-card">
diff --git a/apps/frontend/src/app/features/sites/site-detail/site-detail.scss b/apps/frontend/src/app/features/sites/site-detail/site-detail.scss
index 78dd9ed..a0032be 100644
--- a/apps/frontend/src/app/features/sites/site-detail/site-detail.scss
+++ b/apps/frontend/src/app/features/sites/site-detail/site-detail.scss
@@ -74,6 +74,11 @@
   font-weight: 700;
 }
 
+.card__unavailable {
+  color: var(--color-text-muted);
+  margin: 0;
+}
+
 .metrics-grid {
   display: grid;
   grid-template-columns: repeat(2, 1fr);
diff --git a/apps/frontend/src/app/features/sites/site-detail/site-detail.spec.ts b/apps/frontend/src/app/features/sites/site-detail/site-detail.spec.ts
index 3fdc269..5e3cf46 100644
--- a/apps/frontend/src/app/features/sites/site-detail/site-detail.spec.ts
+++ b/apps/frontend/src/app/features/sites/site-detail/site-detail.spec.ts
@@ -116,6 +116,86 @@ describe('SiteDetail', () => {
     expect(fixture.componentInstance.site()).toBeNull();
   });
 
+  it('efface les données du site précédent quand le chargement du suivant échoue', () => {
+    const getSite = vi
+      .fn()
+      .mockReturnValueOnce(of(SITE))
+      .mockReturnValueOnce(throwError(() => new Error('404')));
+    const { fixture, paramMap } = setup(
+      'SITE001',
+      { getSite, getCurrent: vi.fn().mockReturnValue(of(CURRENT_COMPLET)) },
+      { getHistory: vi.fn().mockReturnValue(of([LECTURE])) },
+    );
+
+    fixture.detectChanges();
+    expect(fixture.componentInstance.site()?.site_id).toBe('SITE001');
+
+    paramMap.next(convertToParamMap({ siteId: 'SITE002' }));
+    fixture.detectChanges();
+
+    expect(fixture.componentInstance.error()).not.toBeNull();
+    expect(fixture.componentInstance.site()).toBeNull();
+    expect(fixture.componentInstance.current()).toBeNull();
+    expect(fixture.componentInstance.history()).toEqual([]);
+    expect(fixture.nativeElement.textContent).not.toContain('Site 1');
+  });
+
+  it('interroge le site et sa mesure courante en parallèle', () => {
+    const getSite = vi.fn().mockReturnValue(of(SITE));
+    const getCurrent = vi.fn().mockReturnValue(of(CURRENT_COMPLET));
+    const { fixture } = setup(
+      'SITE001',
+      { getSite, getCurrent },
+      { getHistory: vi.fn().mockReturnValue(of([])) },
+    );
+
+    fixture.detectChanges();
+
+    expect(getSite).toHaveBeenCalledWith('SITE001');
+    expect(getCurrent).toHaveBeenCalledWith('SITE001');
+  });
+
+  it('signale la panne du capteur de consommation au lieu de tracer une jauge à zéro', () => {
+    const sansConsommation = {
+      ...CURRENT_COMPLET,
+      consumption_kw: null,
+      null_reasons: ['consumption_sensor_failure'],
+      data_quality: 'partial' as const,
+    };
+    const { fixture } = setup(
+      'SITE001',
+      {
+        getSite: vi.fn().mockReturnValue(of(SITE)),
+        getCurrent: vi.fn().mockReturnValue(of(sansConsommation)),
+      },
+      { getHistory: vi.fn().mockReturnValue(of([LECTURE])) },
+    );
+
+    fixture.detectChanges();
+
+    expect(fixture.componentInstance.consumptionKw()).toBeNull();
+    expect(fixture.componentInstance.consumptionReason()).toBe('capteur de consommation en panne');
+    expect(fixture.nativeElement.querySelector('app-consumption-gauge')).toBeNull();
+    expect(fixture.nativeElement.textContent).toContain('Consommation indisponible');
+  });
+
+  it('trace la jauge pour une consommation nulle réellement mesurée', () => {
+    const { fixture } = setup(
+      'SITE001',
+      {
+        getSite: vi.fn().mockReturnValue(of(SITE)),
+        getCurrent: vi.fn().mockReturnValue(of({ ...CURRENT_COMPLET, consumption_kw: 0 })),
+      },
+      { getHistory: vi.fn().mockReturnValue(of([LECTURE])) },
+    );
+
+    fixture.detectChanges();
+
+    expect(fixture.componentInstance.consumptionLabel()).toBe('0.0 kW');
+    expect(fixture.nativeElement.querySelector('app-consumption-gauge')).not.toBeNull();
+    expect(fixture.nativeElement.textContent).not.toContain('Consommation indisponible');
+  });
+
   it('affiche explicitement les champs null avec leur raison plutôt que de les masquer', () => {
     const partielle = {
       ...CURRENT_COMPLET,
diff --git a/apps/frontend/src/app/features/sites/site-detail/site-detail.ts b/apps/frontend/src/app/features/sites/site-detail/site-detail.ts
index 047614a..21e716d 100644
--- a/apps/frontend/src/app/features/sites/site-detail/site-detail.ts
+++ b/apps/frontend/src/app/features/sites/site-detail/site-detail.ts
@@ -1,7 +1,7 @@
 import { Component, DestroyRef, computed, inject, signal } from '@angular/core';
 import { takeUntilDestroyed, toObservable, toSignal } from '@angular/core/rxjs-interop';
 import { ActivatedRoute, RouterLink } from '@angular/router';
-import { catchError, EMPTY, filter, map, Observable, of, switchMap } from 'rxjs';
+import { catchError, EMPTY, filter, forkJoin, map, Observable, of, switchMap } from 'rxjs';
 import { SitesService } from '../../../core/services/sites.service';
 import { ReadingsService } from '../../../core/services/readings.service';
 import { Site } from '../../../shared/models/site.model';
@@ -52,8 +52,14 @@ interface MetricDef {
   format: (value: number) => string;
 }
 
+const CONSUMPTION_DEF: MetricDef = {
+  key: 'consumption_kw',
+  label: 'Consommation',
+  format: (v) => `${v.toFixed(1)} kW`,
+};
+
 const METRIC_DEFS: MetricDef[] = [
-  { key: 'consumption_kw', label: 'Consommation', format: (v) => `${v.toFixed(1)} kW` },
+  CONSUMPTION_DEF,
   { key: 'voltage_v', label: 'Tension', format: (v) => `${v.toFixed(1)} V` },
   { key: 'current_a', label: 'Courant', format: (v) => `${v.toFixed(1)} A` },
   { key: 'power_factor', label: 'Cos φ', format: (v) => v.toFixed(2) },
@@ -111,6 +117,15 @@ export class SiteDetail {
 
   hasMeasurement = computed(() => this.current()?.timestamp != null);
 
+  consumptionKw = computed(() => this.current()?.consumption_kw ?? null);
+
+  consumptionLabel = computed(() => {
+    const kw = this.consumptionKw();
+    return kw != null ? CONSUMPTION_DEF.format(kw) : null;
+  });
+
+  consumptionReason = computed(() => this.reasonFor('consumption_kw', this.current()));
+
   qualityLabel = computed(() => {
     const quality = this.current()?.data_quality;
     return quality ? LIBELLE_PAR_QUALITE[quality] : null;
@@ -156,10 +171,10 @@ export class SiteDetail {
   }
 
   private load(siteId: string) {
-    return this.sitesService.getSite(siteId).pipe(
-      switchMap((site) =>
-        this.sitesService.getCurrent(siteId).pipe(map((current) => ({ site, current }))),
-      ),
+    return forkJoin({
+      site: this.sitesService.getSite(siteId),
+      current: this.sitesService.getCurrent(siteId),
+    }).pipe(
       switchMap(({ site, current }) =>
         this.loadHistory(siteId, current).pipe(map((history) => ({ site, current, history }))),
       ),
@@ -186,8 +201,13 @@ export class SiteDetail {
     return trouvees.length > 0 ? trouvees.join(', ') : 'cause inconnue';
   }
 
+  // Piège : vider les signaux avec l'erreur, sinon la page garde le site précédemment chargé
+  // sous le bandeau et laisse lire les chiffres de A en croyant regarder B.
   private reportUnavailable(): Observable<never> {
     this.error.set(UNAVAILABLE_MESSAGE);
+    this.site.set(null);
+    this.current.set(null);
+    this.history.set([]);
     return EMPTY;
   }
 }
diff --git a/apps/frontend/src/app/shared/components/reading-history-chart/reading-history-chart.spec.ts b/apps/frontend/src/app/shared/components/reading-history-chart/reading-history-chart.spec.ts
index bb6232f..63be883 100644
--- a/apps/frontend/src/app/shared/components/reading-history-chart/reading-history-chart.spec.ts
+++ b/apps/frontend/src/app/shared/components/reading-history-chart/reading-history-chart.spec.ts
@@ -9,15 +9,21 @@ vi.mock('chart.js', () => {
     static register = vi.fn();
     update = vi.fn();
     destroy = vi.fn();
-    data = { datasets: [{}] };
-    constructor() {
+    data: { labels?: unknown[]; datasets: Record<string, unknown>[] } = { datasets: [{}] };
+    constructor(_canvas: unknown, config?: { data?: ChartMock['data'] }) {
+      if (config?.data) {
+        this.data = config.data;
+      }
       ChartMock.instances.push(this);
     }
   }
   return { Chart: ChartMock, registerables: [] };
 });
 
-type ChartDouble = { destroy: ReturnType<typeof vi.fn> };
+type ChartDouble = {
+  destroy: ReturnType<typeof vi.fn>;
+  data: { labels?: unknown[]; datasets: Record<string, unknown>[] };
+};
 
 function lastChart(): ChartDouble | undefined {
   return (Chart as unknown as { instances: ChartDouble[] }).instances.at(-1);
@@ -66,6 +72,21 @@ describe('ReadingHistoryChart', () => {
     expect(() => fixture.detectChanges()).not.toThrow();
   });
 
+  it("trace du plus ancien au plus récent, quel que soit l'ordre reçu de l'API", () => {
+    TestBed.configureTestingModule({ imports: [ReadingHistoryChart] });
+    const fixture = TestBed.createComponent(ReadingHistoryChart);
+    // L'API trie en timestamp décroissant : le composant doit rétablir la chronologie.
+    fixture.componentRef.setInput('readings', [
+      { ...READING, reading_id: 2, timestamp: '2026-09-17T11:00:00Z', consumption_kw: 60 },
+      { ...READING, reading_id: 1, timestamp: '2026-09-17T10:00:00Z', consumption_kw: 42 },
+    ]);
+    fixture.detectChanges();
+
+    const chart = lastChart();
+    expect(chart?.data.labels).toEqual(['2026-09-17T10:00:00Z', '2026-09-17T11:00:00Z']);
+    expect(chart?.data.datasets[0]['data']).toEqual([42, 60]);
+  });
+
   it('détruit le graphique quand le composant est détruit', () => {
     TestBed.configureTestingModule({ imports: [ReadingHistoryChart] });
     const fixture = TestBed.createComponent(ReadingHistoryChart);
diff --git a/apps/frontend/src/app/shared/components/reading-history-chart/reading-history-chart.ts b/apps/frontend/src/app/shared/components/reading-history-chart/reading-history-chart.ts
index 922ca01..17d1e06 100644
--- a/apps/frontend/src/app/shared/components/reading-history-chart/reading-history-chart.ts
+++ b/apps/frontend/src/app/shared/components/reading-history-chart/reading-history-chart.ts
@@ -20,8 +20,23 @@ const QUALITY_COLORS: Record<ReadingDataQuality, string> = {
 };
 const UNKNOWN_QUALITY_COLOR = '#9ca3af';
 
-function pointColors(readings: Reading[]): string[] {
-  return readings.map((r) => (r.data_quality ? QUALITY_COLORS[r.data_quality] : UNKNOWN_QUALITY_COLOR));
+interface ChartSeries {
+  labels: string[];
+  values: number[];
+  colors: string[];
+}
+
+// Piège : l'API renvoie les lectures du plus récent au plus ancien (ReadingRepository.list_history
+// trie en timestamp desc) ; sans ce tri l'axe des abscisses se lirait à rebours.
+function toSeries(readings: Reading[]): ChartSeries {
+  const ordered = [...readings].sort((a, b) => Date.parse(a.timestamp) - Date.parse(b.timestamp));
+  return {
+    labels: ordered.map((r) => r.timestamp),
+    values: ordered.map((r) => r.consumption_kw ?? 0),
+    colors: ordered.map((r) =>
+      r.data_quality ? QUALITY_COLORS[r.data_quality] : UNKNOWN_QUALITY_COLOR,
+    ),
+  };
 }
 
 @Component({
@@ -38,27 +53,27 @@ export class ReadingHistoryChart implements AfterViewInit, OnDestroy {
 
   constructor() {
     effect(() => {
-      const readings = this.readings();
+      const series = toSeries(this.readings());
       if (this.chart) {
-        this.chart.data.labels = readings.map((r) => r.timestamp);
-        this.chart.data.datasets[0].data = readings.map((r) => r.consumption_kw ?? 0);
-        this.chart.data.datasets[0].pointBackgroundColor = pointColors(readings);
+        this.chart.data.labels = series.labels;
+        this.chart.data.datasets[0].data = series.values;
+        this.chart.data.datasets[0].pointBackgroundColor = series.colors;
         this.chart.update('none');
       }
     });
   }
 
   ngAfterViewInit(): void {
-    const readings = this.readings();
+    const series = toSeries(this.readings());
     this.chart = new Chart(this.canvasRef.nativeElement, {
       type: 'line',
       data: {
-        labels: readings.map((r) => r.timestamp),
+        labels: series.labels,
         datasets: [
           {
-            data: readings.map((r) => r.consumption_kw ?? 0),
+            data: series.values,
             borderColor: '#3b82f6',
-            pointBackgroundColor: pointColors(readings),
+            pointBackgroundColor: series.colors,
             tension: 0.25,
           },
         ],