Discussion:
Need help with gas furnace problem
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David Ananas
2003-10-23 12:15:22 UTC
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Gas furnace: Ko-Z-Aire, Model 90 GV, Rated Input/Output per hour:
90,000/72,000 BTU

PilotStat: Honeywell, Type C418A1

Location: Baltimore, MD

Here is the problem: The furnace stopped turning on recently even when
we set the thermostat to very high. The thermostat has two wires (red
and white).

Jumpered the two wires at the thermostat, still didn't fire up.

The furnace has a magnetic gas valve. Jumpered the two wires at the
valve (disconnected the two wires at the thermostat since the manual
says not to do it because it is bad for the thermostat, why?), the
furnace DID fire up!

The two wires from thermostat: One goes directly to gas valve, one
through the PilotStat, so it seems the PilotStat is the problem. Only
two things are connected to the PilotStat: the electric wires (one
goes to thermostat wire, the other to gas valve) and a thermocouple.
Replaced the thermocouple with a brand new one from Home Depot to no
avail.

So:

1. Did I diagnose the problem correctly, that it is the PilotStat that
is the problem?

2. How do I find a replacement for this PilotStat? Can I just get a
generic PilotStat instead of the original part? Where from and how do
I find the correct match? I have no idea how old it is. The house was
built around 1955.

3. Just a side question, what is the PilotStat doing anyway? Right
now, the pilot burner keeps burning (although now we have turned the
gas input off so it is completely dead). Is this PilotStat supposed to
control the gas input to the pilot burner? If the burner is always on,
and the electric on-off switch is controlled by the thermostat, why do
we need a PilotStat? Is it OK to just bypass the PilotStat altogether,
and connect the two wires from the thermostat directly to the magnetic
gas valve?

Thanks, folks, for any help!

David
TURTLE
2003-10-23 16:28:01 UTC
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Post by David Ananas
90,000/72,000 BTU
PilotStat: Honeywell, Type C418A1
Location: Baltimore, MD
Here is the problem: The furnace stopped turning on recently even when
we set the thermostat to very high. The thermostat has two wires (red
and white).
Jumpered the two wires at the thermostat, still didn't fire up.
The furnace has a magnetic gas valve. Jumpered the two wires at the
valve (disconnected the two wires at the thermostat since the manual
says not to do it because it is bad for the thermostat, why?), the
furnace DID fire up!
The two wires from thermostat: One goes directly to gas valve, one
through the PilotStat, so it seems the PilotStat is the problem. Only
two things are connected to the PilotStat: the electric wires (one
goes to thermostat wire, the other to gas valve) and a thermocouple.
Replaced the thermocouple with a brand new one from Home Depot to no
avail.
1. Did I diagnose the problem correctly, that it is the PilotStat that
is the problem?
2. How do I find a replacement for this PilotStat? Can I just get a
generic PilotStat instead of the original part? Where from and how do
I find the correct match? I have no idea how old it is. The house was
built around 1955.
3. Just a side question, what is the PilotStat doing anyway? Right
now, the pilot burner keeps burning (although now we have turned the
gas input off so it is completely dead). Is this PilotStat supposed to
control the gas input to the pilot burner? If the burner is always on,
and the electric on-off switch is controlled by the thermostat, why do
we need a PilotStat? Is it OK to just bypass the PilotStat altogether,
and connect the two wires from the thermostat directly to the magnetic
gas valve?
Thanks, folks, for any help!
David
This is Turtle.

I can't just get a good picture of what type system you have. From what you
say here i'm taking it you have Mill volt type system with a Pilot lite
Millvolt generator. If this system is another type such as central air gas
furnace with ductwork and blower to circulate air through out your house.
I'm all wrong here. I'm will speak you as have a Gravity type system with
maybe a small electric blower in it to circulate some air in the room it is
in.

Other names of what I'm talking about
Gravity heating systems
Wall furnaces
Wall mount inferay heaters
Floor mount gravity heating system.

The pilotstat as you speak of is the power supply to open the gas valve and
have from 250 millvolt to 750 millvolts to control with. this pilotstat you
say will have a thermocouple attached to it and leads to the flame of the
pilot lite and directly infront of flame of pilot lite. When a person has
intermitte problem with the system working and and stops for no reason. It
usely is 1 of two things.

1) The Millvolt generator is defective and needs to be replaces but you
need the exact millvolt rating of the generator.
2) the pilot lite is just a little dirty and does not let enough flame hit
the generator to generate enough millvolts to open the gas valve. Clean the
polit jet out and get flame back on the millvolt thermocouple generator. It
will look the same as a hot water tank pilot lite thermocouple but usely it
will be fatter that a 24 volt thermocouple used on hot water tanks.

What i think you have a dirty pilot lite jet and not getting enough of flame
to the thermocouple.

TURTLE
Harvey
2017-01-06 16:44:01 UTC
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replying to David Ananas, Harvey wrote:
Did you get your problem solved? I realize it has been a long time since you
posted but I am having the same problem, THANKS!

--
for full context, visit https://www.homeownershub.com/maintenance/need-help-with-gas-furnace-problem-480242-.htm
m***@yahoo.com
2017-01-06 22:20:40 UTC
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Post by Harvey
Did you get your problem solved? I realize it has been a long time since you
posted but I am having the same problem, THANKS!
--
for full context, visit https://www.homeownershub.com/maintenance/need-help-with-gas-furnace-problem-480242-.htm
come over here to usenet alt.home.repair instead of home owners hub and you will be better off.

in any case

if you jump the wires at the Tstadt and no furnace

but

when you jump __the same two wires__ at the furnace and it does come on,

that means there is either a loose connection or the wire in the wall is broken.

m

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