CWLee wrote:

How does a "vent safety switch" work?

I'm trouble-shooting a friend's gas furnace (Empire Comfort Systems
Model #GW-25-6). I have isolated the problem to what the instruction
booklet calls a "manual reset vent safety switch." It says this safety
device will switch off the gas flow if "the ventilation is not proper"
or similar wording. I'm trying to figure out if the switch is
defective, or if there is a ventilation problem. I'm satisfied that the
pilot and burner mechanism work properly, and that the thermostat works
properly. Nevertheless, the furnace shuts off unexpectedly, but will
restart promptly if the vent safety switch is reset, meaning a button on
it is pushed.

What variable does the switch sense in order to determine if the
ventilation is proper?

My first thought is that it is temperature, and that if the temperature
of the air around it is above some threshold the switch cuts off the
electric current that is keeping the gas valve open.

My second hypothesis is that the switch senses air flow (how would it do
that?) and if the speed of air passing the switch is below some
threshold the switch cuts off the electric current that is keeping the
gas valve open.

Enlightenment, explanations, elaborations, etc. appreciated.


Is this a wall furnace? Would the model number start with "GWT" instead
of "GW"? If it is what I think it is and the vent safety switch is not
defective, the vent cap on the roof could be messed up. Of course it
would help to know if it's a gravity vented wall furnace.

TDD

"The Daring Dufas" wrote:

Is this a wall furnace?

Yes.

Would the model number start with "GWT" instead
of "GW"?

I may have failed to record the letter T - I do make
mistakes now and then - but I'm pretty sure it is as I
listed it. I'll have a chance to double check later today,
or perhaps tomorrow.

If it is what I think it is and the vent safety switch is
not
defective, the vent cap on the roof could be messed up. Of
course it
would help to know if it's a gravity vented wall furnace.

Yes, it appears to be gravity vented. Here is more info I
recorded but failed to post:

Gravity Vented Wall Furnace
ANS Z21.49b-1995 wall furnace
Model# GW-25-6
Serial# P-43-451101
Input btu/hr 25,000
Gas nat

Does that additional info help you?

Thanks.

CWLee wrote:


"The Daring Dufas" wrote:

Is this a wall furnace?

Yes.

Would the model number start with "GWT" instead
of "GW"?

I may have failed to record the letter T - I do make mistakes now and
then - but I'm pretty sure it is as I listed it. I'll have a chance to
double check later today, or perhaps tomorrow.

If it is what I think it is and the vent safety switch is not
defective, the vent cap on the roof could be messed up. Of course it
would help to know if it's a gravity vented wall furnace.

Yes, it appears to be gravity vented. Here is more info I recorded but
failed to post:

Gravity Vented Wall Furnace
ANS Z21.49b-1995 wall furnace
Model# GW-25-6
Serial# P-43-451101
Input btu/hr 25,000
Gas nat

Does that additional info help you?

Thanks.



Yea, I thought it may be a wall furnace. The newest models are the
"GWT". The vent safety switch is a simple bi-metal manual reset
thermal switch. It is the equivalent of the "roll out switch" on
forced air furnaces that will shut one of that type down if the
flames roll out of the burner assembly. In your case, the baffle
where the safety switch is located will overheat when the hot flue
exhaust spills out into the living space. If the pipe that vents
the furnace through the roof is somehow damaged or blocked, this
could be causing the problem. You could probably feel the hot exhaust
spilling out past the baffle with your hand when the burners light
up. You might get something like a yucky cigarette to watch if the
smoke from it is blown back into the room instead of being pulled up
the stack by the draft. If you get a good draft up the vent stack,
there is a possibility that the safety switch has become too sensitive.
I've seen it happen before to temperature switches but it's rare.

TDD

TDD beat me to the reply. Another possibility of flue gas not venting
properly even with the vent pipe clean and intact is that the room is in
a negative pressure and the gases are being sucked out of the draft
diverter. The air going up the vent pipe has to be replaced by outside
air somehow. Usually, especially with a small furnace like this one,
enough air leakage occurs naturally. However, a fireplace or anything
else that pulls air out of the house can cause a negative. Larry

CWLee wrote:


"The Daring Dufas" wrote:

Is this a wall furnace?

Yes.

Would the model number start with "GWT" instead
of "GW"?

I may have failed to record the letter T - I do make mistakes now and
then - but I'm pretty sure it is as I listed it. I'll have a chance to
double check later today, or perhaps tomorrow.

If it is what I think it is and the vent safety switch is not
defective, the vent cap on the roof could be messed up. Of course it
would help to know if it's a gravity vented wall furnace.

Yes, it appears to be gravity vented. Here is more info I recorded but
failed to post:

Gravity Vented Wall Furnace
ANS Z21.49b-1995 wall furnace
Model# GW-25-6
Serial# P-43-451101
Input btu/hr 25,000
Gas nat

Does that additional info help you?

Thanks.




Go to alt.hvac. Their friendly members are experts and would gladly help
you.

Lp1331 1p1331 wrote:
TDD beat me to the reply. Another possibility of flue gas not venting
properly even with the vent pipe clean and intact is that the room is in
a negative pressure and the gases are being sucked out of the draft
diverter. The air going up the vent pipe has to be replaced by outside
air somehow. Usually, especially with a small furnace like this one,
enough air leakage occurs naturally. However, a fireplace or anything
else that pulls air out of the house can cause a negative. Larry


Years ago I lived in a house with a fireplace and every time the
bathroom vent was turned on, we smelled the odor of burning wood.
The bathroom vent was pulling air back down the chimney into the
house. Same thing can happen with a clothes dryer that is vented
to the outside.

TDD

Cheerfully, and with smiles. Be sure to mention you think
it's a bad thermostat.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"zimpzampzormp" wrote in
message ...

Go to alt.hvac. Their friendly members are experts and would
gladly help
you.

I was installing a furnace in a house, the owners lit up a
wood fire in the fire place. The make up air aparently came
right down the furnace flue, which brought in about 99%
woodsmoke, and nearly choked me to death.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"The Daring Dufas" wrote
in message ...

Years ago I lived in a house with a fireplace and every time
the
bathroom vent was turned on, we smelled the odor of burning
wood.
The bathroom vent was pulling air back down the chimney into
the
house. Same thing can happen with a clothes dryer that is
vented
to the outside.

TDD

"Stormin Mormon" wrote:

Be sure to mention you think
it's a bad thermostat.

I don't think the thermostat is bad. I think it is a
thermostatic vent safety switch that is bad, a different
device.

Does that make sense to you?

Thanks.

CWLee wrote:
"Stormin Mormon" wrote:

Be sure to mention you think
it's a bad thermostat.

I don't think the thermostat is bad. I think it is a
thermostatic vent safety switch that is bad, a different
device.

Does that make sense to you?

Just don't go to the hvac group unless you like being abused.

You havn't been on alt.hvac? I call it alternating havoc.
It's been a bit slow, lately. But mentioning a thermosat
there. It's like throwing bloody chum to starving
alligators. Take a couple Valium before reading the replies.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"CWLee" wrote in message
...


"Stormin Mormon" wrote:

Be sure to mention you think
it's a bad thermostat.

I don't think the thermostat is bad. I think it is a
thermostatic vent safety switch that is bad, a different
device.

Does that make sense to you?

Thanks.

Yes, it makes perfect sense. Now, the questions. Is there
really a venting problem, or is the switch growing weak?
Does the switch read pressure, air flow, or temperature?

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"CWLee" wrote in message
...


"Stormin Mormon" wrote:

Be sure to mention you think
it's a bad thermostat.

I don't think the thermostat is bad. I think it is a
thermostatic vent safety switch that is bad, a different
device.

Does that make sense to you?

Thanks.

"Stormin Mormon" wrote:

Now, the questions. Is there
really a venting problem, or is the switch growing weak?

That's exactly what I'm trying to determine.

Does the switch read pressure, air flow, or temperature?

An off-line continuation of this thread with one of the
posters leads me to believe that it is a temperature sensing
device. It may be called a thermodisk or thermodisc. I'm
told the red dot on it signifies that it trips at 195
degrees.

One of my ideas is to remove it, take it to a
heating/plumbing supply store, and see if I can match it.
Once I have it removed I may be able to do some bench
testing to see if it is working. My off-line advisor said
the switch should "click" when it is reset. So far, I can't
get it to click, but access is difficult so I'm suspending
judgment until I have it off the furnace.

Thanks for your continuing assistance.

Many snap disk have a temperature number on there, some
where. Maybe the wall heater manufacture can sell you a new
one, and be done with it.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"CWLee" wrote in message
m...


"Stormin Mormon" wrote:

Now, the questions. Is there
really a venting problem, or is the switch growing weak?

That's exactly what I'm trying to determine.

Does the switch read pressure, air flow, or temperature?

An off-line continuation of this thread with one of the
posters leads me to believe that it is a temperature sensing
device. It may be called a thermodisk or thermodisc. I'm
told the red dot on it signifies that it trips at 195
degrees.

One of my ideas is to remove it, take it to a
heating/plumbing supply store, and see if I can match it.
Once I have it removed I may be able to do some bench
testing to see if it is working. My off-line advisor said
the switch should "click" when it is reset. So far, I can't
get it to click, but access is difficult so I'm suspending
judgment until I have it off the furnace.

Thanks for your continuing assistance.

In article ,
"Stormin Mormon" wrote:

Many snap disk have a temperature number on there, some
where. Maybe the wall heater manufacture can sell you a new
one, and be done with it.


They're about as generic as a piece of string. Likely the mfr. will ask
10x the price of any parts house.