Why is my furnace blowing cold air sometimes? Why is my heat not coming on?

Question

There is nothing more disheartening than to discover my own heat furnace blowing cold air in the middle of the winter months. One day when I came back home and I realised that my whole house felt kinda cold. At first, I thought it must be because the weather outside is too cold and that's the reason why my heat furnace is unable to catch up with heating my whole house. I shrugged it off for the first time it happened assuming it to be something one off happening once only. Anyways, I was very tired coming back from work and I didn't want to have to deal with this problem that day. I just put on some extra warm clothes and did my daily chores and snuggled into my warm blanket.

In the middle of the night I did feel some heat coming back from the furnace vent in my room but it wasn't very warm enough. Barely felt like room temperature air was coming from the air vent in my room. Again I felt back to sleep and didn't bother to investigate the problem. Well, in the morning when I got off my bed, the whole house felt so cold and my hardwood floor was chilly to the touch. I quickly turned on the hot water tap and enjoyed the warmth of the hot tap water for a while.

Now I knew something wasn't quite right with my heat furnace. When I bought this house three years ago, I didn't know how long the furnace had been the previous owner and if they had changed a new furnace or not. As long as it was working I wasn't complaining much about the heat furnace. Having spent much of my money into purchasing this house I think I would like to fix the heat furnace problem myself rather than call a heat furnace repair man. I don't want to spent further expenses on repair work as my pocket has become shallow now.

My sibling had called a heat furnace repair man one day to check on his heat furnace which wasn't working and he was charged $60 just for taking a look without any work being done. The repair man came to his house, inspected the heat furnace and gave two options: repair the worn out parts or buy a new furnace. My sibling went with the option of buying a new heat furnace but he still had to pay for the repair man's visitation fees. The repair man told him that it would cost quite a lot of money to fix the furnace problem and that he is better off buying a new heat furnace unit. Repair man mentioned that he would waive the fees if my sibling bought a new unit from their company. My sibling didn't end up buying with that company.

Answer 1

The most common reason why your heat furnace was blowing old air lies with the problem with your flame sensor. 

1. Flame sensor looks like the picture below:

You should open up your heater furnace front metal and you should see something like this picture below:

See the white wire with the pink tip connector? You need to unscrew that flame sensor and using a semi rough Scotch Brite Scrubber to clean out the carbon dust on the long metal tip of flame sensor.

After cleaning the metal portion of the flame sensor, screw the parts back onto the metal plate and test to see if your heat furnace works or not. If it does not work, then this flame sensor may need to be replaced with a new parts. You can order the parts from Amazon.ca.

2. Your heat furnace air filter may be dirty and needs to be replaced with a new one. Usually heat filter can last for a month or two and needs to be replaced, if you don't want your heat furnace to work extra hard to get air circulation going through.

3. Check to see if all the rubber pipes inside the heat furnace is intact and that none of the rubber pipes had slipped or popped out on its own. In my case, i found a rubber pipes had slipped out on its own due to the regular vibration of the heat furnace. I reattached the rubber pipes and my heat furnace was working fine after that.

4. Sometimes you may need to change the position of the flame sensor to make it work.

Example: if you look at the picture above, the flame sensor is located at the left position. If it doesn't work, you can relocate your flame sensor to the right side of the metal frame if there is a hole for it to be screwed onto. For my heat furnace, i noticed that the flames on the leftmost position was starting at a very late stage and the flame sensor was sensing no flames and shutting the heat furnace right away. So i placed the flame sensor onto the right side position where the flames starts first. This way, the flame sensor will sense the flames first and will not shut down the heat furnace unit.

Flame sensor is a safety feature created by the manufacturer to prevent the unburned natural gas from entering the house vents throughout the house. Unburned natural gas can be potentially deadly if inhaled in large quantity. When the Flame sensor senses no flames present, then it shuts down the whole heat furnace unit.

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