Lennox Furnaces - Flame Sensor warning

[Zero102]

We had one installed in our house just over 5 years ago and when we had the really cold spell in December our furnace shut down. Checking the lights showed a slow alternating blink (watchdog mode). After searching on the internet I found out this was likely just a dirty flame sensor. I used needle nose pliers to remove the wire (its on there TIGHT) then removed the 1/4" sheet metal screw that holds it in and wiped it down/scrubbed it with a paper towel. After re-installing it the furnace has been working perfectly for over 1 month now (where before it would only kick on for 30 seconds at a time). When I looked at the sensor it only had a very light white dust on it, if I didn't know better I would have said it looked perfectly fine.

We first noticed the problem when the house had problems keeping close to the set temperature. We would set the thermostat to 20*C but the temperature would vary from 16*C to 20*C and the furnace seemed to be cycling short. It did this for about 2 months until one day it just wouldn't kick on at all (waking up to a 3*C house sucks).

I was over at my dad's place the other day scanning some pictures and I heard his furnace start doing exactly the same thing. I go down and check the thermostat and it was 4*C below the set temperature (and showed calling for heat). I checked his furnace and sure enough, slow alternating blinking...

Both of our furnaces are just over 5 years old and are Lennox mid-efficiency furnaces. I just wanted to warn anybody else with a similar furnace about this issue. Hopefully it will save somebody some big bucks when they don't have to call an emergency furnace/hvac guy because their furnace shut down at night on a weekend during winter.


Cliff's Notes:
If you have a Lennox mid-efficiency furnace and are cold, it's probably your flame sensor and it can be fixed for free.

[eblend]

Do you live in evergreen?

My friends furnace shut down on them recently, apparently it is a big issue in evergreen as they all use the same furnace and never cleaned them out when they finished construction. This is what the furnace repair person said, he asked if he was in Evergreen as the first question.

This is good to know, don't have any issues myself but if I do this will be the first thing I will check

[rage2]

I had this happen a few years ago too. Always check the sensor first. Some sensors can't be fixed like that, and need replacement. Best thing to do is to find out the part # of the sensor your furnace uses, and buy some spares. They tend to go out every 5-6 years. It's fairly easy to replace, even for a home improvement idiot like myself.

[alloroc]

When you change/clean your air filter every three months also vacuum out the furnace including the fan (turn it off first - duh) and give the sensor a few wipes with a dry q-tip.

A clean furnace is a safe furnace.

[Czar]

While you're getting spares, you might as well get a spare ignitor as well.

Usually it's either the ignitor or the flame sensor. The flame sensor is pretty cheap though, so I usually replace both of them at the same time..

[Zero102]

eblend:
No, I live in Mount Pleasant (new furnace in an old house) and my dad lives in Cougar Ridge.

How expensive are the flame sensors? I haven't checked I was just happy I found a way to fix it for free

[mr2mike]

Good tip. I've got new furnaces but will remember this when the time comes.

[digi355]

I'll bump this, woke up this morning and the house was cold. The furnace was starting up, but it wasn't firing. After some looking I found the flame sensor. It was in a real awkward place, but I managed to get it pulled out. Again, as mentioned above it was covered in a white dust. I Sandpapered it off, put it back in, and turned the furnace back on. No Dice.

I did some more reading and eventually pulled the pressure sensor hoses off. Sure enough one of them had water in it thus stopping the burner from firing. I blew out the hoses (they look like bent pencils and are red and black) and plugged them back in. Turned the furnace back on and she fired.

$150 - 200 saved thanks to in start to this thread.

[Zero102]

Water in the pressure sensor hoses? That's a new one to me

[Pacman]

Where can you buy a flame sensor for a Lennox furnace in Calgary?

The two places I found in the phone book said they would only sell to contractors, not the general public.

[The_Penguin]

Originally posted by Pacman
Where can you buy a flame sensor for a Lennox furnace in Calgary?

The two places I found in the phone book said they would only sell to contractors, not the general public.

Every time I have to buy Lennox furnace parts (fscking Lennox POS furnaces!!, usually it's an expensive controller board too grrr) I get them at Chesney's on 41st Ave NE

[G]

Amry Supply has them

https://www.amresupply.com/part/52W2...SOR-KIT-LB-749

[AndyL]

Plan ahead and order some on ebay... You can get the factory units for 10$ (at least for mine) local is 40-60$. Always tape a spare ignitor and sensor to the side (but make sure its out of your wife's sight as mine moved my last spares and they still haven't reappeared)