diff --git a/lambda/TODO b/lambda/TODO
index 3b5a2e1..135e3c1 100644
--- a/lambda/TODO
+++ b/lambda/TODO
@@ -14,5 +14,4 @@
 - Makefile: LANG = 0
 - pins.h LCD pins
 - interrupts.h TIMER0_COMP_MATCH 122/244 (124/248)
-- sensors.h: SHUNT_MILLIOHMS 100 (111)
-- rules.c: heaterTimeout(): getTime() >= 10800
\ No newline at end of file
+- sensors.h: SHUNT_MILLIOHMS 100 (111)
\ No newline at end of file
diff --git a/lambda/rules.c b/lambda/rules.c
index 6173c5c..d5f5846 100644
--- a/lambda/rules.c
+++ b/lambda/rules.c
@@ -140,8 +140,8 @@
 		return;
 	}
 	if (meas.current > milliAmpsShort || meas.current < milliAmpsDisconn ||
-			(getTime() >= 180 && meas.current > milliAmpsReady)) {
-		// short circuit or disconnected or did not warm up within 3 minutes
+			(getTime() >= 300 && meas.current > milliAmpsReady)) {
+		// short circuit or disconnected or did not warm up within 5 minutes
 		setHeaterOn(false);
 		setHeaterState(heaterStateFault);
 		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_HEATER_FAULT_0),
@@ -150,12 +150,12 @@
 }
 
 /**
- * Switches the heater off if it is still on after 3 hours and there does
+ * Switches the heater off if it is still on after 15 mins and there does
  * not seem to be a fire.
  */
 static void heaterTimeout(bool* const fired, int8_t const dir,
 		Measurement const meas) {
-	if (isHeaterOn() && getTime() >= 10800 && meas.tempI < TEMP_AIRGATE_0) {
+	if (isHeaterOn() && getTime() >= 900 && meas.tempI < TEMP_FIRE_OUT) {
 		setHeaterOn(false);
 		alert_P(3, 5, TONE, PSTR(MSG_HEATER_OFF_0),
 				PSTR(MSG_HEATER_OFF_1), false);
@@ -163,6 +163,22 @@
 }
 
 /**
+ * Switches the heater on if it is off and not in state fault and it seems
+ * obvious that there is a fire building up.
+ */
+static void heaterOn(bool* const fired, int8_t const dir,
+		Measurement const meas) {
+	if (isHeaterOn() || getHeaterState() == heaterStateFault) {
+		return;
+	}
+	if (dir != burning_down && meas.tempI > TEMP_AIRGATE_0) {
+		setHeaterOn(true);
+		alert_P(3, 5, TONE, PSTR(MSG_HEATER_UP_0),
+				PSTR(MSG_HEATER_UP_1), false);
+	}
+}
+
+/**
  * Rules applied to every nth averaged measurement.
  */
 Rule rules[] = {
@@ -180,7 +196,8 @@
 Rule heaterRules[] = {
 		{false, heaterReady},
 		{false, heaterFault},
-		{false, heaterTimeout}
+		{false, heaterTimeout},
+		{false, heaterOn}
 };
 
 int8_t getDir(void) {
@@ -217,12 +234,12 @@
 	if (age >= AGE_MEAS_PREV) {
 		dir = none;
 		if ((meas.tempI - rulesMeasPrev.tempI) >= TEMP_DELTA_UP &&
-				rulesMeasMax.tempI < TEMP_MAX && meas.lambda >= LAMBDA_MAX) {
+				rulesMeasMax.tempI < TEMP_MIN && meas.lambda >= LAMBDA_MAX) {
 			dir = firing_up;
-		} else if (meas.tempI > TEMP_AIRGATE_0 && meas.lambda < LAMBDA_MAX) {
+		} else if (meas.tempI > TEMP_MIN || meas.lambda < LAMBDA_MAX) {
 			dir = burning;
 		} else if ((rulesMeasPrev.tempI - meas.tempI) >= TEMP_DELTA_DOWN &&
-				rulesMeasMax.tempI > TEMP_MAX && meas.lambda >= LAMBDA_MAX) {
+				rulesMeasMax.tempI > TEMP_MIN && meas.lambda >= LAMBDA_MAX) {
 			dir = burning_down;
 		} else if ((meas.tempI - rulesMeasPrev.tempI) >= TEMP_DELTA_UP) {
 			// it seems wood has been added - reset some measurements and rules
@@ -232,7 +249,7 @@
 			for (size_t i = 0; i < rulesSize; i++) {
 				rules[i].fired = false;
 			}
-			if (! isHeaterOn()) {
+			if (! isHeaterOn() && getHeaterState() != heaterStateFault) {
 				setHeaterOn(true);
 			}
 		}
diff --git a/lambda/rules.h b/lambda/rules.h
index 13ccee5..4b94fea 100644
--- a/lambda/rules.h
+++ b/lambda/rules.h
@@ -18,7 +18,7 @@
 /** Age of previous measurements to compare against */
 #define AGE_MEAS_PREV 180
 /** Oven reaches at least this temperature when the fire is burning */
-#define TEMP_MAX 800
+#define TEMP_MIN 700
 /** Min. increase in temperature during AGE_MEAS_PREV when firing up */
 #define TEMP_DELTA_UP 10
 /** Min. decrease in temperature during AGE_MEAS_PREV when burning down */
@@ -26,7 +26,7 @@
 /** Min. temperature at which to set the air gate to 50% when firing up  */
 #define TEMP_AIRGATE_50 500
 /** Max. temperature at which to set the air gate to 25% when burning down */
-#define TEMP_AIRGATE_25 800
+#define TEMP_AIRGATE_25 700
 /**
  * Max. temperature at which to set the air gate to 0% and to switch off the
  * oxygen sensor heater when burning down
diff --git a/lambda/sensors.c b/lambda/sensors.c
index a37c0c9..e140069 100644
--- a/lambda/sensors.c
+++ b/lambda/sensors.c
@@ -176,7 +176,7 @@
 	size_t size = sizeof(linADCTable) / sizeof(linADCTable[0]);
 	int16_t dev = lookupLinInter(mV, linADCTable, size);
 
-	return (int32_t)mV - dev;
+	return (int32_t)mV == 0 ? 0 : mV - dev;
 }
 
 char* toInfo(uint16_t const lambda) {
diff --git a/lambda/sensors.h b/lambda/sensors.h
index 17b02f6..a4d92c7 100644
--- a/lambda/sensors.h
+++ b/lambda/sensors.h
@@ -19,7 +19,7 @@
  * Oxygen sensor heater current limits at certain states in milliamps.
  */
 typedef enum {
-	milliAmpsReady = 1400,
+	milliAmpsReady = 1350,
 	milliAmpsShort = 7500,
 	milliAmpsDisconn = 100
 } HeaterMilliAmps;