Gas furnace cycles every 1 - 5 minutes

[Rudy Taraschi]

Hi folks,

I'm having problems with my Amana 80 gas furnace. Every few minutes, the flame will shut off, and immediately, the igniter powers up, gas valve opens, and the flame lights again. A couple of minutes later, the flame shuts off and the cycle repeats. It's real cold (-24C/-11F) if that makes any difference.

What I've done so far:

1) sanded the flame sensor, which wasn't really dirty - no change 2) shielded the backflow sensor from heat - no change 3) checked the trouble code LED - no codes 4) both fans work 5) chimney relay did not trip

Any ideas or experiences to share would be much appreciated.

[Matt]

You have a decision:

A) Continue playing with something you have no clue about. B) Call someone who can fix it. Follow any advice but B at your own peril.

[~KJPRO~]

Un-shield the so called 'back flow sensor'!

Next if your design temp is close to the actual temps you are experiencing, maybe the stat is calling for heat before the fan shuts down. If not there is a definite problem.

I suggest you call an HVAC company to clean and inspect the unit. When was the last time it was done?

~kjpro~

[Rudy Taraschi]

Sorry I wasn't clear in my original post. I shielded the sensor for just long enough to see that the problem still occurred (a couple of minutes with me watching like a hawk). I did not bypass it permanently.

The fan is set up to run constantly. On my thermostat, this is called "Emergency heat" mode; the furnace is set up to use this switch to shut off the heatpump during deep freeze temperatures (basically January and February).

You're the second person to suggest the thermostat (I got another answer by private email because the person did not feel like getting flamed publicly if he said something wrong). My symptoms are exactly like someone sitting at the thermostat (old mercury style) and moving the setpoint above and below ambient every few minutes.

I had an HVAC guy do a cursory check about a year ago (furnace is less than 10 years old). I've called for a full service checkup (inspect, clean, etc) and am waiting for an appointmnet. They're pretty busy when it's this cold outside.

Thanks again!

[Gideon]

Matt,

You have passed the first set of criteria for considering a career as a quintessential HVAC professional - smug, critical and offering no useful advice.

Gideon

(My apologies to the HVAC experts who aren't jerks.)

======================

A) Continue playing with something you have no clue about. B) Call someone who can fix it. Follow any advice but B at your own peril.

[Bubba]

Just too damn funny. First its an 80% gas furnace and all of a sudden the heat pump pops into the picture. Best advice you'll ever get:

1) Leave the damn thing alone 2) Call your service company back again (or another company) and tell them your furnace is NOT working properly. This is NOT a freaking tune-up or a clean and check call. You are trying to get off cheap. You need a service call to correct the problem and THEN you can consider getting it cleaned and checked. "Oh my, my furnace is broke but I'll just call for a clean and check so it wont cost so much." You arent fooling anyone and especially you wont fool the tech that comes out. Bubba

[Rudy Taraschi]

Unless I'm missing something, the heatpump is *not* in the picture

- it's switched out. I've been switching out the heatpump when it gets cold for 10+ years. This setup is pretty standard up here in Montreal.

I'm not trying to fix the thing, I'm trying to do my homework and figure out what's wrong so that (a) I don't get fleeced, and (b) if I get a brain donor for a tech, I won't be left with a broken furnace two weeks after he "fixes" it.

The previous two times I had someone over, they were techs from local HVAC service companies. This time, I actually went directly to the Gaz company for their expen$ive techs. I'm not trying to save money, I'm trying to get my furnace fixed, and have time to kill before the tech arrives Saturday morning.

Err ... not really. What I told the phone operator was exactly what I said in my original email. My furnace isn't working right. It does this blah blah blah. Please send someone to check what's wrong, FIX IT, and do a routine service on it while he's here. I logged the call as a "problem" and not a "routine service call".

[kj]

Then he is a pussy, or a clueless Hack like Stormin.

If he was a real pro, he'd have nothing to worry about! People make mistakes, but not to post on the web is just crazy.

Most likely he is afraid to say something wrong cause he/she is a new tech...so be it...they'll never learn if they don't post to find out the correct answers.

If they say something wrong and they get corrected...oh well...they learned something. That's part of it!

No, I didn't say it could be the stat, I said that if you are experiancing around design ambient temps that the stat could be calling for heat soon after the stat is satified.

Which means, your home is loosing heat very rapidly...when the furnace runs amd heats the home to temp...then it doesn't take long for the home to cool and call for heat once again.

kjpro

[TURTLE]

This is Turtle.

After all is said and done it just sounds like the Heat Antisipator is set wrong , not on the thermostat, or burnt. As I have read your using the gas heat as back up to a heat pump but you probley have a heat pump type thermostat on it and some heat pump thermostats don't have antisipators on them to be used in this application. If this is the case your short cycling on having no Heat antisipator on the heat pump thermostat.

TURTLE