diff --git a/heat_control.py b/heat_control.py
index 2974ba9..5c6b9ca 100644
--- a/heat_control.py
+++ b/heat_control.py
@@ -21,8 +21,11 @@ CONFIG_FILE = "config.json"
 # will turn on boiler after this amount of opened contour time
 # (this is to make sure valve has time for opening)
 BOILER_TURN_ON_AFTER = 90
+# will turn off boiler if it's exhaust temperature is too high
+BOILER_EXHAUST_LIMIT = 50
 
 contours = []
+boiler_exhaust_t = 0
 config: Dict[str, Any] = {}
 
 # MQTT client
@@ -72,17 +75,23 @@ def on_connect(client, userdata, flags, rc):
 		for k in contours:
 			client.subscribe(k.sensor_topic)
 			logger.info(f"Subscribed to: {k.sensor_topic}")
+		# and boiler exhaust topic
+		client.subscribe(config.get('boiler_exhaust_t'))
 	else:
 		logger.error(f"Connection failed with code: {rc}")
 
 def on_message(client, userdata, msg):
 	"""MQTT message callback - store temperature values"""
+	global contours, boiler_exhaust_t
 	try:
 		for k in contours:
 			if (k.sensor_topic == msg.topic):
 				temperature = float(msg.payload.decode('utf-8'))
 				k.update(temperature)
 				logger.debug(f"Updated {k.sensor_topic}: {temperature}°C")
+		if msg.topic == config.get('boiler_exhaust_t'):
+			boiler_exhaust_t = float(msg.payload.decode('utf-8'))
+			logger.debug(f"Updated boiler exhaust: {boiler_exhaust_t}°C")
 	except ValueError:
 		logger.error(f"Invalid temperature value: {msg.payload}")
 	except Exception as e:
@@ -94,6 +103,17 @@ any_opened = False
 def check_temperatures():
 	"""Check temperatures against target and control GPIO"""
 	global any_opened_start, any_opened
+	# check boiler exhaust, turn off if too big
+	if (boiler_exhaust_t > BOILER_EXHAUST_LIMIT):
+		logger.error("Boiler exhaust overheat")
+		# will open all contours (to force coolant circulation)
+		# and turn off the boiler of course
+		for c in contours:
+			# valves are normally-opened, so 0 means "open"
+			mqtt_client.publish(c.out_topic, "0", retain=True)
+		mqtt_client.publish(boiler_control, "0", retain=True)
+		return
+	#
 	sum_t = 0
 	count_t = 0
 	for c in contours: