diff --git a/esphome/core/template_lambda.h b/esphome/core/template_lambda.h
index 1977265c33..894b5edffa 100644
--- a/esphome/core/template_lambda.h
+++ b/esphome/core/template_lambda.h
@@ -1,120 +1,51 @@
 #pragma once
 
-#include <functional>
-#include <concepts>
 #include "esphome/core/optional.h"
 
 namespace esphome {
 
-/** Helper class for template platforms that stores either a stateless lambda (function pointer)
- * or a stateful lambda (std::function pointer).
+/** Lightweight wrapper for template platform lambdas (stateless function pointers only).
  *
- * This provides backward compatibility with PR #11555 while maintaining the optimization:
- * - Stateless lambdas (no capture) → function pointer (4 bytes on ESP32)
- * - Stateful lambdas (with capture) → pointer to std::function (4 bytes on ESP32)
- * Total size: enum (1 byte) + union (4 bytes) + padding = 8 bytes (same as PR #11555)
+ * This optimizes template platforms by storing only a function pointer (4 bytes on ESP32)
+ * instead of std::function (16-32 bytes).
  *
- * Both lambda types must return optional<T> (as YAML codegen does) to support the pattern:
- *   return {};  // Don't publish a value
+ * IMPORTANT: This only supports stateless lambdas (no captures). The set_template() method
+ * is an internal API used by YAML codegen, not intended for external use.
+ *
+ * Lambdas must return optional<T> to support the pattern:
+ *   return {};    // Don't publish a value
  *   return 42.0;  // Publish this value
  *
- * operator() returns optional<T>, returning nullopt when no lambda is set (type == NONE).
- * This eliminates redundant "is lambda set" checks by reusing optional's discriminator.
+ * operator() returns optional<T>, returning nullopt when no lambda is set (nullptr check).
  *
- * @tparam T The return type (e.g., float for TemplateLambda<optional<float>>)
+ * @tparam T The return type (e.g., float for sensor values)
  * @tparam Args Optional arguments for the lambda
  */
 template<typename T, typename... Args> class TemplateLambda {
  public:
-  TemplateLambda() : type_(NONE) {}
+  TemplateLambda() : f_(nullptr) {}
 
-  // For stateless lambdas: use function pointer
-  template<typename F>
-  requires std::invocable<F, Args...> && std::convertible_to < F, optional<T>(*)
-  (Args...) > void set(F f) {
-    this->reset_();
-    this->type_ = STATELESS_LAMBDA;
-    this->stateless_f_ = f;  // Implicit conversion to function pointer
-  }
+  /** Set the lambda function pointer.
+   * INTERNAL API: Only for use by YAML codegen.
+   * Only stateless lambdas (no captures) are supported.
+   */
+  void set(optional<T> (*f)(Args...)) { this->f_ = f; }
 
-  // For stateful lambdas: use std::function pointer
-  template<typename F>
-  requires std::invocable<F, Args...> &&
-      (!std::convertible_to<F, optional<T> (*)(Args...)>) &&std::convertible_to<std::invoke_result_t<F, Args...>,
-                                                                                optional<T>> void set(F &&f) {
-    this->reset_();
-    this->type_ = LAMBDA;
-    this->f_ = new std::function<optional<T>(Args...)>(std::forward<F>(f));
-  }
+  /** Check if a lambda is set */
+  bool has_value() const { return this->f_ != nullptr; }
 
-  ~TemplateLambda() { this->reset_(); }
-
-  // Copy constructor
-  TemplateLambda(const TemplateLambda &) = delete;
-  TemplateLambda &operator=(const TemplateLambda &) = delete;
-
-  // Move constructor
-  TemplateLambda(TemplateLambda &&other) noexcept : type_(other.type_) {
-    if (type_ == LAMBDA) {
-      this->f_ = other.f_;
-      other.f_ = nullptr;
-    } else if (type_ == STATELESS_LAMBDA) {
-      this->stateless_f_ = other.stateless_f_;
-    }
-    other.type_ = NONE;
-  }
-
-  TemplateLambda &operator=(TemplateLambda &&other) noexcept {
-    if (this != &other) {
-      this->reset_();
-      this->type_ = other.type_;
-      if (type_ == LAMBDA) {
-        this->f_ = other.f_;
-        other.f_ = nullptr;
-      } else if (type_ == STATELESS_LAMBDA) {
-        this->stateless_f_ = other.stateless_f_;
-      }
-      other.type_ = NONE;
-    }
-    return *this;
-  }
-
-  bool has_value() const { return this->type_ != NONE; }
-
-  // Returns optional<T>, returning nullopt if no lambda is set
+  /** Call the lambda, returning nullopt if no lambda is set */
   optional<T> operator()(Args... args) {
-    switch (this->type_) {
-      case STATELESS_LAMBDA:
-        return this->stateless_f_(args...);  // Direct function pointer call
-      case LAMBDA:
-        return (*this->f_)(args...);  // std::function call via pointer
-      case NONE:
-      default:
-        return nullopt;  // No lambda set
-    }
+    if (this->f_ == nullptr)
+      return nullopt;
+    return this->f_(args...);
   }
 
+  /** Alias for operator() for compatibility */
   optional<T> call(Args... args) { return (*this)(args...); }
 
  protected:
-  void reset_() {
-    if (this->type_ == LAMBDA) {
-      delete this->f_;
-      this->f_ = nullptr;
-    }
-    this->type_ = NONE;
-  }
-
-  enum : uint8_t {
-    NONE,
-    STATELESS_LAMBDA,
-    LAMBDA,
-  } type_;
-
-  union {
-    optional<T> (*stateless_f_)(Args...);     // Function pointer (4 bytes on ESP32)
-    std::function<optional<T>(Args...)> *f_;  // Pointer to std::function (4 bytes on ESP32)
-  };
+  optional<T> (*f_)(Args...);  // Function pointer (4 bytes on ESP32)
 };
 
 }  // namespace esphome
diff --git a/tests/components/template/common-base.yaml b/tests/components/template/common-base.yaml
index 7d2cb19077..f101eea942 100644
--- a/tests/components/template/common-base.yaml
+++ b/tests/components/template/common-base.yaml
@@ -10,26 +10,12 @@ esphome:
         state: !lambda "return 42.0;"
 
     # Test C++ API: set_template() with stateless lambda (no captures)
+    # NOTE: set_template() is not intended to be a public API, but we test it to ensure it doesn't break.
     - lambda: |-
         id(template_sens).set_template([]() -> esphome::optional<float> {
           return 123.0f;
         });
 
-    # Test C++ API: set_template() with stateful lambda (with captures)
-    # This is the regression test for issue #11555
-    - lambda: |-
-        float captured_value = 456.0f;
-        id(template_sens).set_template([captured_value]() -> esphome::optional<float> {
-          return captured_value;
-        });
-
-    # Test C++ API: set_template() with more complex capture
-    - lambda: |-
-        auto sensor_id = id(template_sens);
-        id(template_number).set_template([sensor_id]() -> esphome::optional<float> {
-          return sensor_id->state * 2.0f;
-        });
-
     - datetime.date.set:
         id: test_date
         date: