Gas and Oil Home Heating Furnaces - Gas Furnace Fan keeps coming on, even when

Gas Furnace Fan keeps coming on, even when it's turned "off" on the thermostat.

I have a Gas furnace and central AC. Since we've started using the AC (this is our first summer in this house), the fan keeps coming on - even when the air is off and when the wall thermostat is set to "off" also -

Sometimes it comes all the way on, other times, it just sort of starts/stops/starts/stops - Is the fan supposed to do this? What could be causing this? Thanks in advance..

I've tried replacing the thermostat with another one (new) - This didn't stop it -

The furnace is an armstrong brand and is less then 3 years old - I also have an issue to where the motor (that pumps the excess water out when the AC is on) will not "come on" while the AC is running (thus water spills everywhere) - Though, once the AC is off it pumps its little brains out!!

This motor (pump) is connected into the main "board" of the furnace itself -

I am wondering if the "mother board" of the furnace itself shot (no good).

Why in heavens name would anyone hook a condesate pump to the furnace control board? Turn the power to the furnace off at the breaker or switch (not just at the thermostat), remove the condensate pump wires from the board, put a plug on the end of the cord, & plug it into a recepticle. This might also cure the fan problem but I doubt it. Does this furnace have a pilot which stays lit all the time?

[QUOTE=Grady]Why in heavens name would anyone hook a condesate pump to the furnace control board? Turn the power to the furnace off at the breaker or switch (not just at the thermostat), remove the condensate pump wires from the board, put a plug on the end of the cord, & plug it into a recepticle.
I would suspect the pump needs some sort of control. You surely do not want it running all the time.

It could easily be hooked into the controls for the A/C but apparently are not done correctly in this case.

I'm not sure why they hooked the condensation pump to the mother board itself?? - Though this is an older home and it doesn't necessarily have a close outlet (perhaps this is why).

With that said......it still appears that the mother board doesn't have enough juice or what not to keep the fan running and run the AC at the same time (as I pointed out above...when the AC is on the pump doesn't run......but as soon as I turn the AC off it immeditely comes on and does its job......after the fact).


However....That my fan keeps turning on makes me wonder if it is just not the mother board itself (that is is flawed) and thus while not operating the fan correctly (having it come on and off all the time...regardless of the thermostat being set to "off") perhaps it is also screwing up with my condensation pump as well.


I'll probably have to replace / order a new mother board??


The fan coming on and off every 5-10 minutes regardless of the T-stat being turned to "off" is the biggest issue for me right now

Just trying to figure out whatelse it could possibly be....before I go buy a new mother board.

It is common practice to install a switch & recepticle in the incoming line voltage to the furnace. I do this on every furnace I install for several reasons: (1) It provides a means of shutting off the power which nobody can turn back on & cause me to get the crap knocked out of me while I am working on the furnace. (2) It gives me a place to plug in a drop light or vaccuum cleaner & a convenient place to plug in the condensate pump. (3) Code says there must be a switch within reach while working on the burner. BTW, the recepticle should be on the "hot" side of the switch.

On the fan problem: The pump may have something to do with it. Get the pump off that board first & let's see what happens.

Does the furnace have a pilot which stays lit all the time?

Yes - I do believe this furnace has a pilot light that stays lit all the time - It is an Armstrong brand....Ultra 5 Vantage 80 series -

Also there is a "turn off" swith located right on the furnance itself (which I have turned off now all the time....so as to keep my fan from constatnly turning on and off).

However it is just a power switch with no outlet box / recepticle along with it.....though I guess one could easily be installed there as well??? (and likely should have been when it was installed).

[QUOTE=Grady]It is common practice to install a switch & recepticle in the incoming line voltage to the furnace. I do this on every furnace I install for several reasons

I guess I should have phrased the statement as a question such as: what controls the condensate pump? I was thinking that there may be some sort of control through the a/c itself. If not, then what does control it?

note: this is from a non-HVAC guy.

[QUOTE]

I guess I should have phrased the statement as a question such as: what controls the condensate pump? I was thinking that there may be some sort of control through the a/c itself. If not, then what does control it?

note: this is from a non-HVAC guy.


I "float" type device inside the condensation pump is what triggers it to turn on (regardless of the AC itself) - It simply needs a power source from which to run from - Once that "float" device reaches a certain point (level) it turns on the pump which pumps the water out -

On my system for some reason they choose to tie its power source right to the mother board of the furnace - Which might work fine some times (I don't know).....but my system won't engage the condenstation pump while the AC itself is on (which means water everywhere).....Though once the AC shuts down (desired temp reached on the T-stat) then once the AC is off....the condenstation pump kicks in and pumps water out.

[QUOTE=meade95][QUOTE=nap]
I "float" type device inside the condensation pump is what triggers it to turn on (regardless of the AC itself) - It simply needs a power source from which to run from - Once that "float" device reaches a certain point (level) it turns on the pump which pumps the water out -

Thanks :thumbup:

Try turning the gas off either at the gas valve or the valve in the pipe just before the pipe enters the furnace. I suspect the pilot is generating enough heat to bring on the fan. This is fairly common.
A recpticle could be easily wired in right next to switch. There are switch/receptile combinations which will fit in a standard 2x4box.

Try turning the gas off either at the gas valve or the valve in the pipe just before the pipe enters the furnace. I suspect the pilot is generating enough heat to bring on the fan. This is fairly common.
A recpticle could be easily wired in right next to switch. There are switch/receptile combinations which will fit in a standard 2x4box.


That's what I'll have to do - Put in a recepticle / switch box -

With regard to "turning off the gas" via the gas valve?

Now are you speculating this is turning the fan on for what reason? - Not for cooling the house down purposes??

In that my "fan" seems to run (come on and off) without the need for the AC to be "on" -

Meaning my AC stays off....but just the fan/blower of the furnace runs for short periods of time.....(but I have my T-stat set to "off"......meaning neither the heat nor AC is activated).

Would the pilot still cause the fan itself to turn on?...

Thanks

It is entirely possible & quite common for the pilot to generate enough heat to turn the fan on via a thermal switch in the furnace. The thermostat would have no control over this process.

I have been experiencing EXACTLY the same thing, except my furnace pilot
is a static (or thermal) igniter. So, is it possible that the sensor (indicating that the box is too hot, causing the fan to come on...) is no good?

Perplexed,
Richie333

We get several of these calls every summer..Especially if the furnace is mounted in the attic.. garages also get very warm. The temp exceeds the "on" temp setting of the fan control and the blower is energized. Of course the fan control has to be the thermal type for this to happen. If the unit does not have AC just turn off disconnect for the warm season. If AC equipped run the AC to cool the furnace.

A thermal ignitor would not cause the fan to come on. Sometimes, as mbk3 stated, a hot garage or attic might be enough to trigger the fan if the fan is controled by temperature which in your case, I doubt. Where is your furnace located & can you provide us with a make & model?

My (friends) furnace is located in a very warm attic. It is a GE furnace:

Model #BLH080F936B0 with a
Honeywell S8610F module (controller, that provides the thermal heat
thing to light the gas) and that is switched by a relay
Honeywell 8239 R8222D-1006 (15amp) with 6 terminals connects.and
source power from a 24 volt transformer.

I made sure the filter is clean and all connections are tight. The furnace
starts, lights and runs perfectly. When it shuts off (or when she turns it off),
that's when it starts to starts/stops, starts/stops intermittently -- even runs
for a short time occasionally.. The air conditioning part of the system works
with no problems.

Also, her thermostat works, but is so complicated to run (a crazy early digital
nightmare), and I'm sorry, I don't have the specs. on it.

Thanks for any help you can offer...
Richie333

It is entirely possible the attic is hot enough to bring on the fan if only for a very short time. If there is no attic exhaust fan, I suggest installing one.

Thanks for your input. They do have plans to put in some more attic vents into the eve stops... I will suggest the attic (power) vent...

Only because the thermostat is such a strange (and very difficult) one to operate, I'd like to get them a much simpler one -- just heat/air and maybe time programmable... How do I choose the correct one (what criteria or which specs. should I go by)?

GE Model #BLH080F936B0 gas furnace with a
Honeywell S8610F module (controller?, that provides the thermal heat
thing to light the gas) and that is switched by a relay
Honeywell 8239 R8222D-1006.

I guess that I also wondered if the relay itself might have "seen better
days" (it's the part doing all the clicking, causing the starting/stopping)...
I suspected a short in the area at first -- seemed like every once in a while
when I jostled wires in the area it would do its thing...but all seems ok.

still wondering...
Richie333

The Honeywell "Vision" series are very nice thermostats & easy to program. They are available at most home centers.

One thing to remember about attic exhaust fans is they can only exhaust as much air as can be drawn in via soffit or gable end vents. It is amazing how much cooler an attic can become by using one.

It is possible the relay is sticking or a wire (particularly the one to the "G" terminal) is chaffed & is shorting.

The sq ft of the attic X 0.7 == the cfm of the fan you need up there to vent the attic. make sure you have the vents to let the air in. ;)

Thanks for the info about attic fans capacity (sq ft., etc.).

So can I assume that any Honeywell thermostat (with the features desired)will suffice?

almost there,
Richie333

PS I'll re-check for a short -- as far as the relay possibly sticking... should I just replace it, or is there a way to test/or clean it (like with electrical contact spray)?

If bad board or relay get a new one ;)