Any Furnace guys around?

[Jigger]

Hi guys. I'm having a problem with my furnace. Essentially, it appears to be misfiring. I woke up this morning to a colder than normal temp. of 16deg. The thermostat is set for 18 and up to 22 at 6AM when people start to rise. Got a call from my wife in the late morning telling me it was still the same. I ran her through the do's of how to manually operate the thermostat and did come home to a 20deg house. Which isn't really saying much, it was a fair day today. Anyhow, got the covers off the furnace so I could see the sight glass. When I replaced the bottom panel and the switch activated, there was an initial flame for about 6sec. That was it. For the next 5min, I timed the cycle... After 39sec the light came on, no flame. Another 52sec, light but no flame. Again at 1:17, same thing.

 

Is there something I can do here besides wear a good pair of woolies to bed tonight? Thanks for any help.

 

Edit: Just to add that there is good suction on the intake pipe. Also, when I turn the thermostat from AUTO to RUN, the fan kicks in, but it doesn't want to blow when on the AUTO setting?

Edited March 28, 2012 by Jigger

[danbouck]

I had the same problem last year. I cleaned the metal sensor things lol (cant remember the name) with steel wool and changed the filter.

[Jigger]

I had the same problem last year. I cleaned the metal sensor things lol (cant remember the name) with steel wool and changed the filter.

 

Thanks for the reply Dan. Not sure which sensor you're talking about? Filter is waiting until the weekend as I don't think its my primary problem.

[danbouck]

Flame sensors, clean those up and try that.

 

What it's doing is not sensing a flame so it is shutting down.

[The Urban Fisherman]

It's called a thermocouple and looks like this

 

Dan is exactly right about the heat sensor thingy heh... It's a safety thing to make sure your furnace doesn't keep pumping gas into your house if there's no flame... if it's dirty it won't detect the flame...

 

For example furnaces with pilot lights, the pilot flame usually heat's the thermocouple and the thermocouple sends a signal to the board that says everything is a-ok and that there's flame... if the pilot flame goes out the thermocouple cools down and no longer sends that signal, so the furnace shuts itself down.

 

I don't know for sure if the thermocouple your problem but it was always the first thing we looked at when I was an apprentice... ( I changed career paths shortly after )

 

Does your furnace have flashing lights on it? Usually there's a flashig light that will tell you the main problem based on codes...the codes (combination of flashes) are usually on a sticker on the inside door?

[Gerritt]

Sounds like a possible thermocoupler issue as Dan says. They are inexpensive to replace and if you are somewhat handy you can do it yourself in a couple of minutes.

[Jigger]

Flame sensors, clean those up and try that.

 

What it's doing is not sensing a flame so it is shutting down.

 

Still not sure what they look like Dan, but may done something thats helping. Noticed that when I had both doors off, the switch inside the unit started everything up beauty when I just held it with my thumb. Flame for over 30sec. When I put the door back on, it didn't want to cycle and certainly didn't hold a flame... So I bent the door in a little to engage the switch a little better and The furnace started up real quick! Cycled for 41sec then flame for almost 2minutes!! After that, the intervals were close between flames, approx 1min then would spark up with flame for 16, 8 and 39seconds at a time. Then the furnace stopped. Thermostat still at 20 as we speak. Thanks again Dan. Still not sure what the sensors look like.

[Jigger]

It's called a thermocouple and looks like this

 

Dan is exactly right about the heat sensor thingy heh... It's a safety thing to make sure your furnace doesn't keep pumping gas into your house if there's no flame... if it's dirty it won't detect the flame...

 

For example furnaces with pilot lights, the pilot flame usually heat's the thermocouple and the thermocouple sends a signal to the board that says everything is a-ok and that there's flame... if the pilot flame goes out the thermocouple cools down and no longer sends that signal, so the furnace shuts itself down.

 

I don't know for sure if the thermocouple your problem but it was always the first thing we looked at when I was an apprentice... ( I changed career paths shortly after )

 

Does your furnace have flashing lights on it? Usually there's a flashig light that will tell you the main problem based on codes...the codes (combination of flashes) are usually on a sticker on the inside door?

 

Perfect. Thanks for that guys. I did notice that the light did have a sequence...3flashes followed by 6flashes. I'll have to look for the code on the door I guess. Thanks for the idea guys.

[livinisfishin]

If your furnace has a hot surface ignitor there won't be a thermocouple. The flame sensor is what you are looking for. Its on the opposite side of the ignitor in direct flame contact near the last burner to light. I think it will have 1 wire coming off of it going directly to the board. Remove the screw pull it down and use a fine grit sand paper andd lightly clean it up a bit as suggested. If that was your problem you should be good to go. The code you will most likely getting if that is the issue is " failure to prove ignition". If that isn't the problem post what code you are getting.

[Jigger]

The code is an ope pressure switch. On the diagrams, there are 2, it shows a pressure switch on both of the schematics. The fan still isnt blowing even if i manually hold the switch. The unit fires up for about 6min total and then the code flashes again. Ill give the flame sensor a little cleaning and see if that helps. Thanks again for the replies!

[danc]

Sounds like a flame sensor, as others have mentioned. Basically it a metal probe, about 3/16's in diameter that is seated in direct contact with your ignition flame. Take it out, gently clean it up with some fine sandpaper or emery cloth and you should be good to go. Over time they get dirty, or covered in debris. The debris insulates the probe and prevents it from detecting the heat from the ignition flame quick enough, so the unit shuts down, thinking that ignition has not taken place.

[livinisfishin]

Flame sensor isn't your problem anymore. Could be a number of things...I would love to beable to help you further but I pretty much have to be there to figure it out. Just started getting intothe service thing regularily this winter when I switched companies..the last one I was with was mainly fireplaces. Are you close to barrie?

[Jigger]

No, in brooklin. Thanks anyways.

 

I took the sensor out and gave it a good scrubbing. It came on for a bit but shut off again. Code showing the pressure switch has come on again... Not llokin too good.

[roska]

Thanks for the reply Dan. Not sure which sensor you're talking about? Filter is waiting until the weekend as I don't think its my primary problem.

 

 

Hi jigger

 

The flame sensor

One metal thin rod is dirty

You can take it out and clean with 5dollar bill like a sand paper

Put it back

It should work

But if this thing happen again you need to change it

 

Hopefully will help

Jason

Edited March 29, 2012 by xOmOX

[Blue Lk]

I had a similar problem with an oiler powered boiler last year,it turned out the switch on the power vent line was plugged,if you have a power vent it might be something to check.

[livinisfishin]

Most of "the stuck open pressure switch " problems I've head were weak ventor motors..they were noisy and I knew something was wrong. The other things are plugged drains and hoses. A plugged vent outside( ice or snow build up in the pipe) or anything that can get in there. A lot of times the pressure switches themselves just get weak over time . If I were you I would just make sure your vent is clear and that all the hoses from your ventor motor and pressure switches are free of debris and are firmly connected. Also if you can try and check the condensate drain for obstructions.

[danc]

The code is an ope pressure switch. On the diagrams, there are 2, it shows a pressure switch on both of the schematics. The fan still isnt blowing even if i manually hold the switch. The unit fires up for about 6min total and then the code flashes again. Ill give the flame sensor a little cleaning and see if that helps. Thanks again for the replies!

 

Ok. Since the unit is firing, the pressure switch is working on ignition. Pressure switches get dirty and weak over time too. Take the rubber hoses off of whatever they are connected to, leaving them attached to the switches. Suck and blow (HA! Can't believe I said that ) briskly into the hose several times. You should hear the switch opening or closing by a small click sound. You may have some debris between the contactors in the pressure switch and this may clean them up.

[Viking]

Air switch refers to combustion ventor fan. Could be plugged venting (leaves in inlet pipe),bad air switch or I'd guess condensate drain is plugged. I'd inspect venting and if ok remove and clean all condensate drain lines and also make sure tubes to air switch is clear. Just make sure everything goes back where it came from (as in one tube at a time).

[Viking]

Sorry Dan didn't see your reply

[danc]

Sorry Dan didn't see your reply

 

NP Viking. I actually haven't done residential work in a couple of decades. Most of the hvac units I install now are the size of box cars. But they all work the same way. We,re all here just trying to help.

[Jigger]

Ok. Since the unit is firing, the pressure switch is working on ignition. Pressure switches get dirty and weak over time too. Take the rubber hoses off of whatever they are connected to, leaving them attached to the switches. Suck and blow (HA! Can't believe I said that ) briskly into the hose several times. You should hear the switch opening or closing by a small click sound. You may have some debris between the contactors in the pressure switch and this may clean them up.

 

This is the winner so far. You guys know your stuff!! Thanks so much for your help, the unit is firing for over 2min now with intervals of roughly 40sec and the fan is hauling away!! Cant say it enough, Thanks a ton!

[danc]

This is the winner so far. You guys know your stuff!! Thanks so much for your help, the unit is firing for over 2min now with intervals of roughly 40sec and the fan is hauling away!! Cant say it enough, Thanks a ton!

 

Fantastic Jigger. You owe me a slice of ham.

[GBW]

This is the winner so far. You guys know your stuff!! Thanks so much for your help, the unit is firing for over 2min now with intervals of roughly 40sec and the fan is hauling away!! Cant say it enough, Thanks a ton!

To me it's funny that I had to get the same work done last week too

[Jigger]

Ya Dan it was a treat to get up and feel some warmth for sure! Just let me know if thats a honey glaze or blackforest....

 

Geoff, im really not too sure what to say. Is your wife aware of your extra-curricular activities???

[Spiel]

Ok. Since the unit is firing, the pressure switch is working on ignition. Pressure switches get dirty and weak over time too. Take the rubber hoses off of whatever they are connected to, leaving them attached to the switches. Suck and blow (HA! Can't believe I said that ) briskly into the hose several times. You should hear the switch opening or closing by a small click sound. You may have some debris between the contactors in the pressure switch and this may clean them up.

 

This is exactly what happened to mine a year ago at the beginning of the heating season, on advice from the installer I took the hose off at the one end and blew through to the switch till I could hear it operating. They said it was likely a spider or web blocking it. No issues since.