Today is a snow day after yesterday should have been a snow day and wasn’t, causing a huge traffic jam. This morning when I woke up it was 13 degrees outside and the high today was not supposed to go above freezing, so things weren’t looking good for any snow going away. Around noon I noticed it was kind of cold in the house. I checked the thermostat and it was 61 degrees even though it was set on 66 degrees. I played around with the thermostat for a while, lowering the temperature below 61 degrees and then back up to trigger the switch. I could hear the click of the relay, but I wasn’t getting any heat. I went outside and was surprised that the exhaust for the burner was running. I tried turning on the fan only from the thermostat and it seemed like only the return vents were coming on, not the supply vents. My conclusion was the natural gas wasn’t igniting and therefore the furnace wouldn’t run. Since the furnace doesn’t have a pilot light and just lights itself when needed, there isn’t a lot I can do (like light the pilot light or replace the thermistor, which are about the only things I know to do with a furnace; I went ahead and changed the filter once I went down to the crawlspace).
I called the company that installed the furnace this past Summer, hoping they could get out here today, but figuring there was no way. They didn’t answer but said if it was emergency to press 1 and an on-call tech would contact me. No heat and it is freezing outside seems like an emergency, so I pressed 1, left a message, and they did call me back pretty quickly. I explained what was happening and the tech said the only thing he could think of that I might be able to fix was the drain line for condensate might have frozen and be backing up. I said the drain line goes into the kitchen drain under the house and it isn’t below freezing in the crawlspace (I keep a remote temperature probe down there and have been very glad that it is not getting below freezing despite some very cold temperatures this year). He said they could come out tomorrow and that one thing I could try is turn the system off for 15 minutes, then turn it back on and crank the heat to 75 degrees. He then said he would call me back. I tried doing what he said, but I think that was basically the same thing as I was doing before to get the clicking of the relay. He called back and I told him it wasn’t working.
I decided I really needed to give this thing my best shot at fixing it because it would get very cold in the house as time went on. I found the type of furnace I have (a Lennox EL195) and downloaded a brochure, a user manual, and a technician manual for it. The instructions said to make sure the gas valve was turned to On and that the power switch was on. It showed a gas valve behind the main access panel. So I went down in the crawlspace to take a look. I guess due to the furnace being installed sideways and in a trench, they didn’t use a hinged door, but some metal straps with screws to hold the panel in place. I didn’t bring a screwdriver, so I had to go back in the house and come back. I found the gas valve, which was turned to On. Then I removed a second panel that covers a circuit board. On that circuit board is a LED that blinks off and on slowly. That is a good thing, called the “heartbeat.” But after the burner’s blower stopped blowing, the heartbeat started to blink rapidly. You can count the number of times it blinks before pausing to read an error message written on the control panel. I counted 10 which means “Pressure Switch opened 5 times during one heat demand”. Then I counted the blinks again and came up with 9 blinks. So I counted again for a tie breaker and it seemed to be 9. This means “Pressure Switch failed to close or opened during heat demand”. This didn’t sound like something I could fix. There is actually a little window over the LED so I think you are supposed to be able to see the LED without removed the second panel. Another window looks in near the ignition and I seemed to be able to see a red glow, which I assume was from a functioning glow plug, used to ignite the natural gas.
I went back and read the technical manual for the furnace which went into some detail about the error codes and parts. It said the pressure switch measures the difference in pressure between the intake and exhaust of the burner and if the value is not correct, the furnace won’t come on. They said the usual cause was the intake or exhaust pipes were blocked, but it could also be a lot of other things. I had looked down the exhaust with a flashlight and it didn’t seem blocked, but maybe the intake was clogged with ice or snow? I was able to take the cover off of the intake and look in, but couldn’t see a clog. There was a little ice, so I got my heat gun and knocked the ice off. It wasn’t enough ice to do anything, I don’t think. Anyway, it still didn’t work.
When the power went out many years ago, I learned I could use the stove burners to heat up the kitchen. By putting sheets over the top part of the doorways into the kitchen (there are no doors) I could keep most of the heat from escaping. I was actually able to get the kitchen up to 70 degrees pretty quickly while the rest of the house was at 58 degrees. I cleared off my dining room table so I could move it into the kitchen. That table hasn’t been clear since about 2008, but I got it cleared off and moved it into the kitchen so I could sit down and use my laptop. Austin would walk under the sheets over the doors (there was a big enough gap at the bottom for him to walk through no problem) and lie down on one of the dog beds I brought in, but Katie did not like the sheets at all and wouldn’t come in the kitchen or at least not for long. As I am sitting there editing a localsettings.php file on my laptop at the table in my cozy kitchen, the vent started blowing. I went over to the vent to make sure heat was coming out and it was definitely warm. I had fixed it! The heat kicked off before it got back up to 66 degrees, but I think maybe the furnace was just overheating or something. After a few minutes it came back on and got the house all the way warmed up.