HVAC Questions? Ask an HVAC Expert for Answers ASAP
A furnace, in the domestic context, is device that heats water or air which is either used to provide hot water or to warm building, house or other type of structure. A furnace may be fired by either gas or electricity. Common furnace problems include the furnace not working or not producing adequate heat, the furnace going on and off for no reason or problems with the unit’s fan. Experts have provided answers to a large volume of questions on furnace problems. Some of the most frequently asked question along with their answers are given below.
The most likely cause is a blown fuse. Turn off the power to the furnace. Remove the lower blower door and find the circuit board. In the board there should be a fuse like the ones you have in a car which will typically have a rating of 3 or 5 amps. Check to see if the fuse has blown and if so, replace it with one of the same rating. Turn on the power and check if the unit is functioning properly. If not, the problem could be with the flame rollout switches. If there is a red rest button at the back of the switches press them. If there is no reset switch, you can remove the wires from the switches and use a straightened paper clip to jump the 2 wires together – the R terminal to the W terminal. If the furnace and the blower start the switch is defective and may need to be replaced.
The first thing to do is to check for a defective thermostat. Turn of the power to the unit and remove the R and W wires from the rear of the thermostat and twist them together. The thermostat has been bypassed. Turn on the unit and see if it now operates without switching off- If the problem persists the next step is to check the power supply with a voltmeter. Remove the bottom panel of the furnace. Tape the door switch in and locate the control board. Find terminal L1 and a neutral from where the board received power. Turn the power on and check to see if both L1 and the neutral are getting a constant supply of 120 volts. If the supply is fluctuating, check the wire nuts that connect the high voltage power and ensure they are tight. If the voltage is correct, it is likely that there is a problem with the control board which may require replacement. The suggested course of action would be to have a technician check the board.
Open the big cylinder at the bottom of the unit and hold the door safety switch down with one hand. Watch to see if the burners ignite. I Suspect that they will not which means that the cause of the problem is probably be an open limit switch. Begin by removing the top panel door. The switch is usually square or rectangular in shape and should be inside the furnace cabinet on the wall of the back panel, above the gas valve. There should be 2 wires at the back of the switch. Remove them from the switch and jump twist them together and turn on the unit. If it works properly, the limit switch will probably need to be preplaced.
The most likely cause is a stuck fan relay that keeps the fan running constantly. The relay is mounted on the control board and you may be able to get a temporary fix by tapping the board to free the relay. But the problem will, most likely, reoccur. The best solution will be to replace the board.
Furnaces are complex devices and when handling them care should be taken to avoid electrical shock and heat related injuries. Always follow the instructions given in the owner’s manual when attempting any furnace troubleshooting. If the furnace issues or questions you have are not covered by the manual, having an Expert to help is the best option.