diff --git a/assets/js/components/Config/Markdown.vue b/assets/js/components/Config/Markdown.vue
index ffe7da61d..424778e62 100644
--- a/assets/js/components/Config/Markdown.vue
+++ b/assets/js/components/Config/Markdown.vue
@@ -1,6 +1,6 @@
 <template>
 	<!-- eslint-disable-next-line vue/no-v-html -->
-	<div v-html="compiledMarkdown"></div>
+	<div class="root" v-html="compiledMarkdown"></div>
 </template>
 
 <script>
@@ -18,3 +18,13 @@ export default {
 	},
 };
 </script>
+<style scoped>
+.root {
+	max-width: 100%;
+}
+.root :deep(pre.code) {
+	overflow-x: auto;
+	margin: 1em 0;
+	hyphens: none;
+}
+</style>
diff --git a/plugin/auth/viessmann.go b/plugin/auth/viessmann.go
new file mode 100644
index 000000000..116da2d8e
--- /dev/null
+++ b/plugin/auth/viessmann.go
@@ -0,0 +1,115 @@
+package auth
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/http/cookiejar"
+	"net/url"
+
+	"github.com/evcc-io/evcc/util"
+	"github.com/evcc-io/evcc/util/request"
+	"github.com/evcc-io/evcc/util/transport"
+	"github.com/samber/lo"
+	"golang.org/x/oauth2"
+)
+
+const (
+	OAuthURI    = "https://iam.viessmann.com/idp/v3"
+	RedirectURI = "http://localhost:4200/"
+	// ^ the value of RedirectURI doesn't matter, but it must be the same between requests
+)
+
+func OAuth2Config(clientID string) *oauth2.Config {
+	return &oauth2.Config{
+		ClientID: clientID,
+		Endpoint: oauth2.Endpoint{
+			AuthURL:   OAuthURI + "/authorize",
+			TokenURL:  OAuthURI + "/token",
+			AuthStyle: oauth2.AuthStyleInHeader,
+		},
+		RedirectURL: RedirectURI,
+		Scopes:      []string{"IoT User", "offline_access"},
+	}
+}
+
+func init() {
+	registry.AddCtx("viessmann", NewViessmannFromConfig)
+}
+
+type Viessmann struct {
+	client *http.Client
+	ts     oauth2.TokenSource
+}
+
+func NewViessmannFromConfig(ctx context.Context, other map[string]any) (Authorizer, error) {
+	var cc struct {
+		ClientID       string
+		User, Password string
+	}
+	if err := util.DecodeOther(other, &cc); err != nil {
+		return nil, err
+	}
+
+	v := &Viessmann{
+		client: request.NewClient(util.NewLogger("viessmann")),
+	}
+
+	oc := OAuth2Config(cc.ClientID)
+
+	ctx = context.WithValue(context.Background(), oauth2.HTTPClient, v.client)
+	token, err := v.login(ctx, oc, cc.User, cc.Password)
+	if err != nil {
+		return nil, err
+	}
+
+	v.ts = oc.TokenSource(ctx, token)
+
+	return v, nil
+}
+
+func (v *Viessmann) Transport(base http.RoundTripper) (http.RoundTripper, error) {
+	return &oauth2.Transport{
+		Base:   base,
+		Source: v.ts,
+	}, nil
+}
+
+func (v *Viessmann) login(ctx context.Context, oc *oauth2.Config, user, password string) (*oauth2.Token, error) {
+	cv := oauth2.GenerateVerifier()
+
+	state := lo.RandomString(16, lo.AlphanumericCharset)
+	uri := oc.AuthCodeURL(state, oauth2.S256ChallengeOption(cv))
+
+	v.client.Jar, _ = cookiejar.New(nil)
+	v.client.CheckRedirect = request.DontFollow
+	defer func() {
+		v.client.Jar = nil
+		v.client.CheckRedirect = nil
+	}()
+
+	req, _ := request.New(http.MethodGet, uri, nil, map[string]string{
+		"Authorization": transport.BasicAuthHeader(user, password),
+	})
+
+	resp, err := v.client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusFound {
+		return nil, fmt.Errorf("unexpected status %d", resp.StatusCode)
+	}
+
+	loc, err := url.Parse(resp.Header.Get("Location"))
+	if err != nil {
+		return nil, err
+	}
+	code := loc.Query().Get("code")
+
+	ctx, cancel := context.WithTimeout(ctx, request.Timeout)
+	defer cancel()
+
+	return oc.Exchange(ctx, code, oauth2.VerifierOption(cv))
+}
diff --git a/templates/definition/charger/viessmann.yaml b/templates/definition/charger/viessmann.yaml
new file mode 100644
index 000000000..63bec3526
--- /dev/null
+++ b/templates/definition/charger/viessmann.yaml
@@ -0,0 +1,148 @@
+template: viessmann
+products:
+  - brand: Viessmann
+    description:
+      generic: Heatpump (SG Ready)
+group: heating
+requirements:
+  # evcc: ["sponsorship"]
+  evcc: ["skiptest"]
+  description:
+    de: |
+      Einmalige Warmwasserbereitung auf eine konfigurierbare Solltemperatur. Das Gerät entscheidet eigenständig, ob die Wärmepumpe oder die elektrische Zusatzheizung (falls vorhanden) genutzt wird.
+    en: |
+      One-time hot water preparation to a configurable target temperature. The device automatically decides whether to use the heat pump or the auxiliary electric heater (if available).
+params:
+  - name: user
+    required: true
+    help:
+      de: Registrieren auf [app.developer.viessmann.com](https://app.developer.viessmann.com)
+      en: Register at [app.developer.viessmann.com](https://app.developer.viessmann.com)
+  - name: password
+    required: true
+    help:
+      de: Für den konfigurierten Viessmann Account.
+      en: For the configured Viessmann account.
+  - name: clientid
+    required: true
+    description:
+      de: Client ID
+      en: Client ID
+    help:
+      de: Konfigurieren in [app.developer.viessmann.com](https://app.developer.viessmann.com)
+      en: Configure at [app.developer.viessmann.com](https://app.developer.viessmann.com)
+  - name: gateway_serial
+    required: true
+    description:
+      de: Gateway Serial
+      en: Gateway Serial
+    help:
+      de: Seriennummer des VitoConnect modul (VitoCare App -> Einstellungen -> Kommunikationsmodul -> Seriennummer)
+      en: VitoConnect serial number (VitoCare App -> Settings -> Communication module -> Serial number)
+  - name: installation_id
+    required: true
+    description:
+      de: Installation ID
+      en: Installation ID
+    help:
+      de: siehe https://docs.evcc.io/docs/devices/heating#viessmann
+      en: |
+        Unfortunately you cannot simply lookup this number in the Viessmann app - instead you need to use the following commands on the command line... we're aware this is not for every user, but currently we don't have a better workflow...<br/>
+
+        Prerequisites: curl, jq, and the following parameters:
+
+        ```
+        VIESSMANN_USER=<your-user>
+        VIESSMANN_PASS=<your-password>
+        VIESSMANN_CLIENT_ID=<your-clientid>
+        ```
+
+        Then execute the following (n.b. it's best to paste the entire block as-is, since the intermediate 'CODE' is only valid for 20 seconds):
+
+        ```
+        VIESSMANN_REDIRECT_URI="http://localhost:4200/"
+        VIESSMANN_CODE_CHALLENGE="5M5nhkBfkWZCGfLZYcTL-l7esjPUN7PpZ4rq8k4cmys"
+        VIESSMANN_CODE_VERIFIER="6PygdmeK8JKPuuftlkc6q4ceyvjhMM_a_cJrPbcmcLc-SPjx2ZXTYr-SOofPUBydQ3McNYRy7Hibc2L2WtVLJFpOQ~Qbgic455ArKjUz9_UiTLnO6q8A3e.I_fIF8hAo"
+        ```
+  - name: device_id
+    required: true
+    description:
+      de: Device ID
+      en: Device ID
+    help:
+      de: normalerweise `0`
+      en: typically `0`
+    default: 0
+  - name: target_temperature
+    description:
+      de: Zieltemperatur für Einmal-Warmwasser-Zubereitung (°C)
+      en: Target temperature for one-time charge (°C)
+    help:
+      de: max. 60°C
+      en: max. 60°C
+    required: true
+    default: 45
+    type: int
+render: |
+  type: sgready
+  getmode:
+    source: http
+    uri: https://api.viessmann.com/iot/v2/features/installations/{{.installation_id}}/gateways/{{.gateway_serial}}/devices/{{.device_id}}/features/heating.dhw.oneTimeCharge
+    cache: 2s # to prevent making two identical requests straight after each other for "getmode"
+    auth:
+      source: viessmann
+      user: {{ .user }}
+      password: {{ .password }}
+      clientid: {{ .clientid }}
+    jq: '.data.properties.active.value | if . == false then 1 elif . == true then 2 else . end'
+    # false -> oneTimeCharge is disabled -> normal mode -> 1
+    # true -> oneTimeCharge is enabled -> boost mode -> 2
+  setmode:
+    source: watchdog
+    timeout: 60m # re-write at timeout/2
+    reset: 1 # reset watchdog on normal
+    set:
+      source: switch
+      switch:
+      - case: 1 # normal
+        set:
+          source: http
+          uri: https://api.viessmann.com/iot/v2/features/installations/{{.installation_id}}/gateways/{{.gateway_serial}}/devices/{{.device_id}}/features/heating.dhw.oneTimeCharge/commands/deactivate
+          method: POST 
+          headers:  
+            - content-type: application/json
+          auth:
+            source: viessmann
+            user: {{ .user }}
+            password: {{ .password }}
+            clientid: {{ .clientid }}
+          body: >
+            { }
+      - case: 2 # boost
+        set:
+          source: sequence
+          set:
+          - source: http
+            uri: https://api.viessmann.com/iot/v2/features/installations/{{.installation_id}}/gateways/{{.gateway_serial}}/devices/{{.device_id}}/features/heating.dhw.temperature.temp2/commands/setTargetTemperature
+            method: POST
+            headers:  
+              - content-type: application/json
+            auth:
+              source: viessmann
+              user: {{ .user }}
+              password: {{ .password }}
+              clientid: {{ .clientid }}
+            body: >
+              {"temperature": {{.target_temperature}}}
+          - source: http
+            uri: https://api.viessmann.com/iot/v2/features/installations/{{.installation_id}}/gateways/{{.gateway_serial}}/devices/{{.device_id}}/features/heating.dhw.oneTimeCharge/commands/activate
+            method: POST 
+            headers:  
+              - content-type: application/json
+            auth:
+              source: viessmann
+              user: {{ .user }}
+              password: {{ .password }}
+              clientid: {{ .clientid }}
+            body: >
+              { }