Furnaces can sometimes give you head aches, especially if it's cold outside and you need it more than ever. To make sure you don't need furnace repair services on a winter day, save yourself some time and money and learn how to repair your furnace and keep it in a good condition.First of all, here are some of the major causes you might need furnace repair services: if you have a gas furnace or heater your problems might involve the thermocouple, the pilot right or some component of the electrical system. In order to get access to the pilot burner you have to pull the door out of the furnace housing or, depending on the situation, remove the panel that covers the pilot and gas burners. In an assembly at the front of the furnace you should be able to find everything you need to start your repairs: the pilot light controls, reset buttons, gas valves and the thermocouple.If your gas furnace just won't run, check for blown fuses or tripped circuit breakers at main entrance panel, at separate entrance panel, and on or in furnace and try to restore the circuit. If it's still not receiving power then it's time to get some professional repair services. Also, make sure the the gas valve is fully open and it's receiving fuel. While you're here, check for gas leaks. Here's what you need to do: stir up a mixture of liquid detergent and water and paint this mixture on the gas supply line along its connections and valves. If you have gas leaks then the soapy water will bubble. To repair it. Try tightening the leaking connection with a pipe wrench, but be careful not to over-tighten the connection.If there's not enough heat, maybe the thermostat is set too low or you need to clean or replace the filter. Also make sure all registers are open, or aren't blocked by tugs, drapes or furniture. However, if the burner is dirty you need professional furnace repair service. If you need to replace a thermocouple here is what you need to do: Unscrew the copper lead and connection nut inside threaded connection to gas line. Under the mounting bracket at thermocouple tube, unscrew the bracket nut that holds the tube in place. Then insert the new thermocouple and be sure the steel tube is up can the copper lead is down. Under the bracket, screw bracket nut over tube. Push the connection nut to threaded connection where copper lead connects to gas line. Make sure connection is clean and dry and then tightly screw nut into place, but do not over-tighten it.