HVAC Experts..... I have a question.

[BubsFinn]

Now that the cooler weather has creeped into Texas, I find the need to run my heater from time to time. Lately, it has been cycling on and off very quickly. Like the fan will come on for a second or two then kick off just as it gets up to speed. Then it's off for a few seconds and kicks back on for another second or two. Then off again. The process goes on for 5 or 6 cycles then it comes on and stays on until the room warms up. I can also hear a faint, intermittent rubbing noise from the fan.
I had the whole system replaced less than three years ago so everything is under warranty. What's going on? I have a tech scheduled to come out tomorrow afternoon, but I'd like to get an idea of what's happening.

 

[billanole]

Now that the cooler weather has creeped into Texas, I find the need to run my heater from time to time. Lately, it has been cycling on and off very quickly. Like the fan will come on for a second or two then kick off just as it gets up to speed. Then it's off for a few seconds and kicks back on for another second or two. Then off again. The process goes on for 5 or 6 cycles then it comes on and stays on until the room warms up. I can also hear a faint, intermittent rubbing noise from the fan.
I had the whole system replaced less than three years ago so everything is under warranty. What's going on? I have a tech scheduled to come out tomorrow afternoon, but I'd like to get an idea of what's happening.

??

 

[Moral]

My guess is the flame sensor needs cleaned.

 

[Joes Place]

My guess is the flame sensor needs cleaned.

Yep.
Eventually, it won't be able to start at all when that's too gunked up.

I clean mine every fall, and bought a spare I keep in the furnace room in case it fails entirely.

 

[bagdropper]

The fan rubbing noises might very well be why it cycles off and on quickly.

I'm no HVAC expert, but my bet is if it's a newer unit as you say, there's some sort of shut off sensor if the fan is "struggling"...call it maybe an overload sensor.

Fan gets signal per thermostat to furnace once the heat cycle has begun to turn on. Fan has some sort of obstruction (or is simply faulty) where the system senses abnormally high power draw, and kicks off immediately to save the motor from burning up. Then this series of events repeats itself until it finally has a "free fan" and completes a normal run cycle.


Just guessing of course, but it wouldn't surprise me if it's something along those lines.

 

[DeangeloVickers]

My guess is the flame sensor needs cleaned.

This. It's possible your ignitor is starting to fail but it's start with the flame sense rod.

 

[Joes Place]

I have a tech scheduled to come out tomorrow afternoon, but I'd like to get an idea of what's happening.

Watch exactly what your tech does, because it'll (likely) be super simple for you to DIY and avoid the nuisance of having a furnace not working while you wait for an appointment.

Also, ask him to show you where the fuses in the system boards are (mainly, the 24v control one); those are most likely the same as automotive blade fuses and you can buy yourself a pack of them for $5 and have on hand if one goes out.

I had my wall controller wires come loose and short out the 24v, and was going to have them send out a tech (under warranty) when they told me it's probably the fuse. I just replaced it myself and saved them the trip, because it was beneficial to me to have my system running vs waiting for them to show up (and having to be home when they showed up). Plus, now I have spare fuses and know exactly where to replace if it happens again.

Two replacement parts you want on-hand for your electronic-start furnace are the flame sensor, and the ignitor/glow bar. Both are inexpensive ($10-15) and require just a screwdriver to replace. You can have the tech point those out to you, too, and take phone pics you can label for future reference if you're not super-technical with stuff. If you have a multimeter, you can check your ignitor resistance and see if that's still within spec (typically 45-55 ohms), as those will eventually burn out and read infinite ohms or higher resistance as they age. You get many furnace problems beyond those simple parts, and you need a service guy (like for any of the electronic gas valves, etc); that's not stuff to mess with yourself.

 

[Joes Place]

This. It's possible your ignitor is starting to fail but it's start with the flame sense rod.

The multiple "tries" to start is the kicker here- that's exactly what happens. Systems tries to ramp up, turns on the ignitor and gas and doesn't get the flame sense fast enough due to carbon buildup. It has to sense heat within a second or so, or it shuts the gas off and will try again. After 4 or 5 times, it'll throw a code (might even be blinking a code now)

 

[Joes Place]

Another winter tip for your HVAC system - check your A/C drain trap.

Those dry out, completely, in winter, letting a little air escape through that tube, and small amounts of dirt starts to build up in the trap. Eventually, that will clog the trap, entirely, so when it tries to drain condensation water in the summer, it backs up and starts filling your exchanger with water, which can then drip on to your system/control boards, etc.

A good idea to add a cup or so of water into the trap every month or so over winter to keep it from getting air/dirt running through it that will turn into mud/sludge next summer. You should see clear water coming out the end when you pour water above/before the trap.

My original installer did not include an access point to my trap, and the tech who came out was going to charge $200-300 to "rebuild" it (I had water backed up, dripping inside the system). I just drilled in an access hole and tapped it to add in a removeable cap on the existing PVC, so I can rinse/add water during the dry winter months and keep it from clogging again. I also got some pipe cleaner snakes I can use to clear it out if it does get gunked up again.

 

[BubsFinn]

My guess is the flame sensor needs cleaned.

It's electric, so no flame. Or is that a generic term that applies to electric heaters as well?

 

[DFSNOLE]

It's electric, so no flame. Or is that a generic term that applies to electric heaters as well?

Being in Texas, do you have a heat pump?

 

[BubsFinn]

Being in Texas, do you have a heat pump?

No. I live in a condo and the cost break down didn't pan out for a heat pump. It would have required permission from the HOA and quite a bit of expensive retro fitting.

 

[THE_DEVIL]

Just unplug it, wait 30 seconds and then plug back in. (I find playing elevator music during the interlude helps )

 

[alaskanseminole]

Now that the cooler weather has creeped into Texas, I find the need to run my heater from time to time. Lately, it has been cycling on and off very quickly. Like the fan will come on for a second or two then kick off just as it gets up to speed. Then it's off for a few seconds and kicks back on for another second or two. Then off again. The process goes on for 5 or 6 cycles then it comes on and stays on until the room warms up. I can also hear a faint, intermittent rubbing noise from the fan.
I had the whole system replaced less than three years ago so everything is under warranty. What's going on? I have a tech scheduled to come out tomorrow afternoon, but I'd like to get an idea of what's happening.

Yes, mine short cycles from time-to-time as well and makes me really nervous when I'm tuned into it. I've found that sometimes it's indicative of me needing to change all the filters and when I do so, it corrects itself. Other times, not so much. However, I've had "Ron" my AC guy checking my system 2x per year and it always gets a clean bill of health.

 

[Lindemann]

Being in Texas, do you have a heat pump?

If you have a heat pump then the ignitor and/or sensor isn't the problem. If it's a heat pump I'd look at the outdoor unit capacitor. It's a fairly common failure on a heat pump system.

 

[Joes Place]

It's electric, so no flame. Or is that a generic term that applies to electric heaters as well?

Not a natural gas heater?

If all electric, it's got something funky with a relay then.

 

[Joes Place]

It's electric, so no flame. Or is that a generic term that applies to electric heaters as well?

Might be a multi-stage fan system for the heating elements that's not kicking on properly.

A/C systems have a 'starter capacitor' to give them enough juice to start the motor from a stopped position; when those go out, the fan cannot start or starts too slowly or can stall and can short out fuses.

So, if there's a fan system inside the unit, that may not be kicking in and has a similar issue.

 

[southlakehawk]

This. It's possible your ignitor is starting to fail but it's start with the flame sense rod.

I think this might help your situation Deangelo....just saying

 

[Hawgk]

Another winter tip for your HVAC system - check your A/C drain trap.

Those dry out, completely, in winter, letting a little air escape through that tube, and small amounts of dirt starts to build up in the trap. Eventually, that will clog the trap, entirely, so when it tries to drain condensation water in the summer, it backs up and starts filling your exchanger with water, which can then drip on to your system/control boards, etc.

A good idea to add a cup or so of water into the trap every month or so over winter to keep it from getting air/dirt running through it that will turn into mud/sludge next summer. You should see clear water coming out the end when you pour water above/before the trap.

My original installer did not include an access point to my trap, and the tech who came out was going to charge $200-300 to "rebuild" it (I had water backed up, dripping inside the system). I just drilled in an access hole and tapped it to add in a removeable cap on the existing PVC, so I can rinse/add water during the dry winter months and keep it from clogging again. I also got some pipe cleaner snakes I can use to clear it out if it does get gunked up again.

Good tip. Only thing I’d add is sending a little white vinegar down the drain line about 15 mins before adding fresh water. Keep ahead of the mold and mildew that inevitably builds up and clogs the drain line.

 

[waterboy4582]

No. I live in a condo and the cost break down didn't pan out for a heat pump. It would have required permission from the HOA and quite a bit of expensive retro fitting.

The bullshit being spewed by the posters in this thread is comical. I would just wait and let the tech tell you what is wrong.

 

[onlyTheObvious]

I had something similar. The error codes suggesting something wrong with venting. A bird had tried building a next in exhaust pipe.

go outside and shine flashlight down vent pipe to make sure it’s clear.

 

[waterboy4582]

I had something similar. The error codes suggesting something wrong with venting. A bird had tried building a next in exhaust pipe.

go outside and shine flashlight down vent pipe to make sure it’s clear.

He has an electric furnace so no vent pipe.

 

[onlyTheObvious]

has an electric furnace so no vent pipe.

Maybe he just thinks it is.
…

 

[waterboy4582]

Maybe he just thinks it is.
…

It definitely uses electricity

 

[Joes Place]

Good tip. Only thing I’d add is sending a little white vinegar down the drain line about 15 mins before adding fresh water. Keep ahead of the mold and mildew that inevitably builds up and clogs the drain line.

Have not had this issue, but good suggestion. I'll dump a quarter or half cup into my trap this month.

 

[BubsFinn]

Maybe he just thinks it is.
…

I'm in my mid to late 50s. I know where and where I do not have gas.