diff --git a/README.md b/README.md
index d766302..ce8b818 100755
--- a/README.md
+++ b/README.md
@@ -196,6 +196,10 @@ Activates or deactivates a circuit. See [`SLSetCircuitStateMessage`](#slsetcircu
 
 Sets the heating setpoint for any body. See [`SLSetHeatSetPointMessage`](#slsetheatsetpointmessage) documentation for argument values. Emits the `setPointChanged` event when response is acknowledged.
 
+### setHeatMode(controllerId, bodyType, heatMode)
+
+Sets the preferred heat mode. See [`SLSetHeatModeMessage`](#slsetheatmodemessage) documentation for argument values. Emits the `heatModeChanged` event when response is acknowledged.
+
 ### sendLightCommand(controllerId, command)
 
 Sends a lighting command. See [`SLLightControlMessage`](#sllightcontrolmessage) documentation for argument values. Emits the `sentLightCommand` event when response is acknowledged.
@@ -380,6 +384,17 @@ Passed as an argument to the emitted `setPointChanged` event. The passed version
 * `bodyType` - integer indicating the type of body to set the setpoint of. The pool is body `0` and the spa is body `1`.
 * `temperature` - integer indicating the desired setpoint. This is presumably in whatever units your system is set to (celsius or fahrenheit).
 
+## SLSetHeatModeMessage
+
+Passed as an argument to the emitted `setHeatMode` event. The passed version is empty, however, since the response is just an acknowledgement of receipt of the set command.
+
+### Properties
+
+* `controllerId` - integer indicating the ID of the controller to send this command to.
+  * Note that while `SLControllerConfigMessage` includes a controllerId, this ID, in my experience, should always be 0.
+* `bodyType` - integer indicating the type of body to set the setpoint of. The pool is body `0` and the spa is body `1`.
+* `heatMode` - integer indicating the desired heater mode. Valid values are: 0: "Off", 1: "Solar", 2 : "Solar Preferred", 3 : "Heat Pump", 4: "Don't Change"
+
 ## SLLightControlMessage
 
 Passed as an argument to the emitted `sentLightCommand` event. The passed version is empty, however, since the response is just an acknowledgement of receipt of the light command.
diff --git a/heatmodetest.js b/heatmodetest.js
new file mode 100755
index 0000000..0a1a485
--- /dev/null
+++ b/heatmodetest.js
@@ -0,0 +1,49 @@
+'use strict';
+
+const ScreenLogic = require('./index');
+
+// use this to find and connect to units local to the network this is running on
+var finder = new ScreenLogic.FindUnits();
+finder.on('serverFound', function(server) {
+  finder.close();
+  connect(new ScreenLogic.UnitConnection(server));
+});
+
+finder.search();
+
+// use this if you want to use a direct connection to a known unit
+// connect(new ScreenLogic.UnitConnection(80, '10.0.0.85'));
+
+// use this to remote connect to a system by name (going through the Pentair servers)
+// const systemName = 'Pentair: xx-xx-xx';
+// const password = '1234';
+
+// var remote = new ScreenLogic.RemoteLogin(systemName);
+// remote.on('gatewayFound', function(unit) {
+//   remote.close();
+//   if (unit && unit.gatewayFound) {
+//     console.log('unit ' + remote.systemName + ' found at ' + unit.ipAddr + ':' + unit.port);
+//     connect(new ScreenLogic.UnitConnection(unit.port, unit.ipAddr, password));
+//   } else {
+//     console.log('no unit found by that name');
+//   }
+// });
+
+// remote.connect();
+
+// generic connection method used by all above examples
+function connect(client) {
+  client.on('loggedIn', function() {
+    this.getVersion();
+  }).on('version', function(version) {
+    this.setHeatMode(0, 0, 3);
+    console.log(' version=' + version.version);
+  }).on('heatModeChanged', function() {
+    client.close();
+  }).on('loginFailed', function() {
+    console.log(' unable to login (wrong password?)');
+    client.close();
+  });
+
+  client.connect();
+}
diff --git a/index.js b/index.js
index 5218760..4c4fbc5 100644
--- a/index.js
+++ b/index.js
@@ -210,6 +210,10 @@ class UnitConnection extends EventEmitter {
     this.client.write(new messages.SLSetHeatSetPointMessage(controllerId, bodyType, temperature).toBuffer());
   }
 
+  setHeatMode(controllerId, bodyType, heatMode) {
+    this.client.write(new messages.SLSetHeatModeMessage(controllerId, bodyType, heatMode).toBuffer());
+  }
+
   sendLightCommand(controllerId, command) {
     this.client.write(new messages.SLLightControlMessage(controllerId, command).toBuffer());
   }
@@ -259,6 +263,10 @@ class UnitConnection extends EventEmitter {
         // console.log("  it's a setpoint ack");
         this.emit('setPointChanged', new messages.SLSetHeatSetPointMessage());
         break;
+      case messages.SLSetHeatModeMessage.getResponseId():
+        // console.log("  it's a heater mode ack");
+        this.emit('heatModeChanged', new messages.SLSetHeatModeMessage());
+        break;
       case messages.SLLightControlMessage.getResponseId():
         // console.log("  it's a light control ack");
         this.emit('sentLightCommand', new messages.SLLightControlMessage());
diff --git a/messages/SLSetHeatMode.js b/messages/SLSetHeatMode.js
new file mode 100644
index 0000000..9460915
--- /dev/null
+++ b/messages/SLSetHeatMode.js
@@ -0,0 +1,29 @@
+'use strict';
+
+const SLMessage = require('./SLMessage.js').SLMessage;
+
+const MSG_ID = 12538;
+
+exports.SLSetHeatMode = class SLSetHeatMode extends SLMessage {
+  constructor(controllerIndex, bodyType, heatMode) {
+    super(0, MSG_ID);
+
+    this.controllerIndex = controllerIndex;
+    this.bodyType = bodyType;
+    this.heatMode = heatMode;
+    // heatmodes:
+    // 0: "Off", 1: "Solar", 2 : "Solar Preferred", 3 : "Heat Pump", 4: "Don't Change"
+  }
+
+  encode() {
+    this.writeInt32LE(this.controllerIndex || 0);
+    this.writeInt32LE(this.bodyType || 0);
+    this.writeInt32LE(this.heatMode || 0);
+
+    super.encode();
+  }
+
+  static getResponseId() {
+    return MSG_ID + 1;
+  }
+};
diff --git a/messages/index.js b/messages/index.js
index fdd1c59..d099248 100644
--- a/messages/index.js
+++ b/messages/index.js
@@ -10,4 +10,5 @@ exports.SLVersionMessage = require('./SLVersionMessage.js').SLVersionMessage;
 exports.SLSetCircuitStateMessage = require('./SLSetCircuitStateMessage.js').SLSetCircuitStateMessage;
 exports.SLGetGatewayDataMessage = require('./SLGetGatewayDataMessage.js').SLGetGatewayDataMessage;
 exports.SLSetHeatSetPointMessage = require('./SLSetHeatSetPoint.js').SLSetHeatSetPoint;
+exports.SLSetHeatModeMessage = require('./SLSetHeatMode.js').SLSetHeatMode;
 exports.SLLightControlMessage = require('./SLLightControl.js').SLLightControl;