Arduino LCD with 2 DS18B20. Changing when cycle power - arduino

Question

I'm having a strange problem that I hope someone can help with. My sketch works perfectly when uploaded to my UNO, but when I unplug it and plug it back in, it doesn't work correctly. If I re-upload it, it works again until power is cycled.
Once uploaded, the LCD reads:
Ferm:73.4 73/75
Room:75.1 75/75
After cycling power:
Ferm:73.45 73/18
Room:74.83 75/18
So after cycling power, I now get 2 decimal places and the "high" temp is stuck at "18".
/*
The circuit:
* 5V to Arduino 5V pin
* GND to Arduino GND pin
* CLK to Analog #5
* DAT to Analog #4
*/
// include the library code:
#include "Wire.h"
#include "Adafruit_LiquidCrystal.h"
#include <OneWire.h>
#include <DallasTemperature.h>
//variables for temp readings
float fermTemp;
float fermTempL=100;
float fermTempH=5;
float roomTemp;
float roomTempL=100;
float roomTempH=5;
// set OneWire bus to digital PIN 4 on the Arduino
#define ONE_WIRE_BUS 4
// Setup OneWire instance
OneWire oneWire(ONE_WIRE_BUS);
// Pass oneWire reference to Dallas Temp
DallasTemperature sensors(&oneWire);
// Connect via i2c, default address #0 (A0-A2 not jumpered)
Adafruit_LiquidCrystal lcd(0);
void setup()
{
// set up the LCD's number of rows and columns:
lcd.begin(16, 2);
// turn on backlight
lcd.setBacklight(HIGH);
}
void loop() {
readtemp();
LCDPrint();
}
void readtemp()
{
// get data from sensors
sensors.requestTemperatures();
fermTemp = (sensors.getTempFByIndex(0));
roomTemp = (sensors.getTempFByIndex(1));
// check/set High and Low temp
if (fermTemp<fermTempL) {
fermTempL=fermTemp;
}
if (fermTemp>fermTempH) {
fermTempH=fermTemp;
}
if (roomTemp<roomTempL) {
roomTempL=roomTemp;
}
if (roomTemp>roomTempH) {
roomTempH=roomTemp;
}
}
void LCDPrint()
{
lcd.setCursor(0,0);
lcd.print("Ferm:");
lcd.print(fermTemp,1);
lcd.setCursor(11,0);
lcd.print(fermTempL,0);
lcd.print("/");
lcd.print(fermTempH,0);
lcd.setCursor(0,1);
lcd.print("Room:");
lcd.print(roomTemp,1);
lcd.setCursor(11,1);
lcd.print(roomTempL,0);
lcd.print("/");
lcd.print(roomTempH,0);
}

Answer 1

I counted your characters, 16 per line. If you have a 16X2 display, there might be characters printed beyond the screen. I suspect it was not really 18, but something larger, say 180 or 1800. That could have been a result of failed first attempt to read temperature. This reading is stuck with you as temp High. In your code, you should define a reasonable high temperature, such as 125. Don't update temp High if it is above the reasonable temperature.
To confirm it, print temp High to serial port and inspect the value.