The electric ignitor always starts up correctly (it's not a spark
igniter, it's more like a glow plug).

Sometimes the solenoid for the the gas valve opens and the burners
ignite the main blower comes on and it works fine for about five minutes.

Even when this all works properly, after about five minutes of heating
the burners go out, then the controller tries four times to light them.

When the burners go out, the 24V on the gas valve connections goes away
so the gas valve closes. But when the controller tries to restart the
burners, the ingiter does come on, then there is 24V on the gas valve,
but the gas valve doesn't open (at least I don't smell gas) and the
burners don't ignite.

What is it that is tripping and thinking that the gas needs to be shut
down in the first place? Why doesn't the gas turn back on when the 24V
is on the gas valve terminals?

I don't think it's the flame sensor, because the gas should come on when
the burners try to be ignited then the controller only turns off the gas
if the flame sensor doesn't detect a flame.

The draft inducer motor runs fine, and pulling off the hose, there is
air coming out. I bypassed the pressure sensing switch (you have to have
in open in order for the system to start, then closed once the draft
inducer is running) to see if it was failing, and even with it bypassed
the gas still shuts off long before the thermostat temperature is reached.

I bypassed the three firebox flame-out sensors (one by one) and it
didn't help (I did not try bypassing all three at a time).

Any ideas? I would say it's the gas valve but since it works fine, one
time, I wonder how likely intermittent operation is.

The flashing trouble code LED just indicates "fail to ignite," and
indicates that the trouble could be the gas valve, the gas pressure from
the supply, or the flame sensor.

It's an old Sears Furnace, probably 25 years old. I can't find the model
number anywhere. The gas valve is a White-Rodgers 36E36 227. How hard is
it to replace these. It looks like just removing the pipes from the gas
supply and the manifold. I'm just worried about damaging the manifold if
it's really tight.

SMS wrote:
The electric ignitor always starts up correctly (it's not a spark
igniter, it's more like a glow plug).

Sometimes the solenoid for the the gas valve opens and the burners
ignite the main blower comes on and it works fine for about five minutes.

Even when this all works properly, after about five minutes of heating
the burners go out, then the controller tries four times to light them.

When the burners go out, the 24V on the gas valve connections goes away
so the gas valve closes. But when the controller tries to restart the
burners, the ingiter does come on, then there is 24V on the gas valve,
but the gas valve doesn't open (at least I don't smell gas) and the
burners don't ignite.

What is it that is tripping and thinking that the gas needs to be shut
down in the first place? Why doesn't the gas turn back on when the 24V
is on the gas valve terminals?

I don't think it's the flame sensor, because the gas should come on when
the burners try to be ignited then the controller only turns off the gas
if the flame sensor doesn't detect a flame.

The draft inducer motor runs fine, and pulling off the hose, there is
air coming out. I bypassed the pressure sensing switch (you have to have
in open in order for the system to start, then closed once the draft
inducer is running) to see if it was failing, and even with it bypassed
the gas still shuts off long before the thermostat temperature is reached.

I bypassed the three firebox flame-out sensors (one by one) and it
didn't help (I did not try bypassing all three at a time).

Any ideas? I would say it's the gas valve but since it works fine, one
time, I wonder how likely intermittent operation is.

The flashing trouble code LED just indicates "fail to ignite," and
indicates that the trouble could be the gas valve, the gas pressure from
the supply, or the flame sensor.

It's an old Sears Furnace, probably 25 years old. I can't find the model
number anywhere. The gas valve is a White-Rodgers 36E36 227. How hard is
it to replace these. It looks like just removing the pipes from the gas
supply and the manifold. I'm just worried about damaging the manifold if
it's really tight.
Hi,
Doee the furnace have a flame sensor? Then that is prime suspect. Clean
it and try again. Furnace usually goes into lock up mode when
it fails to stay running after ignition(safety issue). It usually stay
locked up an hour or two. If you want to reset it turn the power on/off.
No blinking LED indicator to spell out the trouble code?

On 11/11/2012 6:49 PM, Tony Hwang wrote:

Hi,
Doee the furnace have a flame sensor? Then that is prime suspect. Clean
it and try again. Furnace usually goes into lock up mode when
it fails to stay running after ignition(safety issue). It usually stay
locked up an hour or two. If you want to reset it turn the power on/off.
No blinking LED indicator to spell out the trouble code?

As I wrote above,

The flashing trouble code LED just indicates "fail to ignite," and
indicates that the trouble could be the gas valve, the gas pressure from
the supply, or the flame sensor.

A bad flame sensor would not stop the burners from igniting, it would
just shut them down when the controller looked at the flame sensor and
didn't see an indication that the flame was present (I've had that
happen on a water heater).

As I understand the operation, the controller checks the flame sensor
maybe 5-10 seconds _after_ the gas valve opens and the burners light (to
give some time for the flame to heat up the sensor). But in this case
the gas valve doesn't open to start the flame. So yes, it's almost
certainly the flame sensor that's the reason the system shuts down, but
the reason there's no flame is because the gas valve isn't opening. I do
see the controller trying to open the gas valve (24V on the gas valve
terminals) but there is no gas.

Things I tried:

Ignite the flame manually in case the glow plug ignitor wasn't hot
enough. No effect because I don't think the gas is on.

Checked that the gas valve is getting 24V shortly after the glow plug
ignitor is ready. The valve is getting 24V. The main solenoid coil is
energized (can feel the magnetic force when it gets 24V). I can't feel
anything on the secondary solenoid.

Checked that none of the flame-out sensors or pressure switch sensor was
tripped (but this is obviously the case since the controller would not
even try to energize the gas valve if any sensor was tripped).

I'm pretty sure that it's a flaky gas valve. One HVAC tech wrote: "Make
sure you have a 24 volt signal to the gas valve terminals. If you do and
it doesn't light, the gas valve is bad." This is exactly what is happening.

On 11/12/2012 5:20 AM, wrote:

Given the above and the other symptoms, I would suspect
either a bad gas valve or some kind of blockage in the
gas lines. With the similar gas valves I've had, you could
also hear it click when energized. If the valve is failing, but
not completely shot, it may open sometimes, then later
perhaps warm up, go open, causing the gas to then shut
off again.

The thing I don't understand is why the gas valve opens before the
thermostat temperature is reached. I suspect that the solenoid is
occasionally able to open the valve but then as it heats up it releases
it, then the flame goes out and the flame sensor removes the 24V from
the valve. But verifying this sequence is difficult.

I hooked up two volt meters, one to the gas valve connection and one to
the flame sensor in an attempt to see the sequence of things.

1. If the furnace is cold:

The hot surface ignitor comes on
24V goes to the gas valve
The gas valve opens
The burners ignite
The hot surface ignitor goes off
The flame sensor goes high
About five minutes later the gas valve closes and the flame sensor goes
low, but I can't see which happens first with a volt meter (need a logic
analyzer).

2. If the furnace is warm:

The hot surface ignitor comes on
24V goes to the gas valve
The gas valve opens
The burners ignite
The hot surface ignitor goes off
A few seconds later the gas valve closes and the flame sensor goes low,
but I can't see which happens first with a volt meter (need a logic
analyzer).

It seems to me that the gas valve is opening too soon after the burners
ignite for it to be the flame sensor causing it to open; I don't know
how many seconds the controller waits before looking at the flame sensor.

3. If the furnace is hot:

The hot surface ignitor comes on
24V goes to the gas valve
The gas valve doesn't open
The burners don't ignite
The flame sensor stays low
The hot surface ignitor goes off
A few seconds 24V is removed from the gas valve, presumably because the
flame sensor doesn't detect a flame.

It's number 3 that leads me to believe that it's got to be the gas
valve. In this case the gas valve isn't opening at all even with 24V on it.

On 11/12/2012 9:27 AM, SMS wrote:
On 11/12/2012 5:20 AM, wrote:

Given the above and the other symptoms, I would suspect
either a bad gas valve or some kind of blockage in the
gas lines. With the similar gas valves I've had, you could
also hear it click when energized. If the valve is failing, but
not completely shot, it may open sometimes, then later
perhaps warm up, go open, causing the gas to then shut
off again.

The thing I don't understand is why the gas valve opens before the

I mean "...why the gas valve closes..."

thermostat temperature is reached. I suspect that the solenoid is
occasionally able to open the valve but then as it heats up it releases
it, then the flame goes out and the flame sensor removes the 24V from
the valve. But verifying this sequence is difficult.

I hooked up two volt meters, one to the gas valve connection and one to
the flame sensor in an attempt to see the sequence of things.

1. If the furnace is cold:

The hot surface ignitor comes on
24V goes to the gas valve
The gas valve opens
The burners ignite
The hot surface ignitor goes off
The flame sensor goes high
About five minutes later the gas valve closes and the flame sensor goes
low, but I can't see which happens first with a volt meter (need a logic
analyzer).

2. If the furnace is warm:

The hot surface ignitor comes on
24V goes to the gas valve
The gas valve opens
The burners ignite
The hot surface ignitor goes off
A few seconds later the gas valve closes and the flame sensor goes low,
but I can't see which happens first with a volt meter (need a logic
analyzer).

It seems to me that the gas valve is opening too soon after the burners
ignite for it to be the flame sensor causing it to open; I don't know
how many seconds the controller waits before looking at the flame sensor.

3. If the furnace is hot:

The hot surface ignitor comes on
24V goes to the gas valve
The gas valve doesn't open
The burners don't ignite
The flame sensor stays low
The hot surface ignitor goes off
A few seconds 24V is removed from the gas valve, presumably because the
flame sensor doesn't detect a flame.

It's number 3 that leads me to believe that it's got to be the gas
valve. In this case the gas valve isn't opening at all even with 24V on it.

On Nov 12, 12:27*pm, SMS wrote:
On 11/12/2012 5:20 AM, wrote:

Given the above and the other symptoms, I would suspect
either a bad gas valve or some kind of blockage in the
gas lines. *With the similar gas valves I've had, you could
also hear it click when energized. *If the valve is failing, but
not completely shot, it may open sometimes, then later
perhaps warm up, go open, causing the gas to then shut
off again.

The thing I don't understand is why the gas valve opens before the
thermostat temperature is reached. I suspect that the solenoid is
occasionally able to open the valve but then as it heats up it releases
it, then the flame goes out and the flame sensor removes the 24V from
the valve. But verifying this sequence is difficult.

I hooked up two volt meters, one to the gas valve connection and one to
the flame sensor in an attempt to see the sequence of things.

1. If the furnace is cold:

The hot surface ignitor comes on
24V goes to the gas valve
The gas valve opens
The burners ignite
The hot surface ignitor goes off
The flame sensor goes high
About five minutes later the gas valve closes and the flame sensor goes
low, but I can't see which happens first with a volt meter (need a logic
analyzer).

2. If the furnace is warm:

The hot surface ignitor comes on
24V goes to the gas valve
The gas valve opens
The burners ignite
The hot surface ignitor goes off
A few seconds later the gas valve closes and the flame sensor goes low,
but I can't see which happens first with a volt meter (need a logic
analyzer).

Yes, I see what you mean. You can''t see what happens first. You
could connect a volt meter on the gas valve and then stand there and
watch the fire. If the control circuitry
is shutting off the gas for some reason, then you should see
the voltage go away and the flame go out at the same time. If the
gas valve is closing on it's own, then you
might be able to see a couple seconds between the flame
first going out, then the voltage on the gas valve going away
as the controller senses no flame and cuts it off.

Alternatively, if you suspect the gas valve is bad and
the coil goes open after it gets warmed up after a bit,
here is what I'd do. Close the gas shut-off valve to the
furnace so no gas can flow. Then jumper 24V direct to
the gas valve for 15 mins. Then remove the jumper, turn
the gas back on and try to start the furnace.

On 11/12/2012 10:45 AM, wrote:

Alternatively, if you suspect the gas valve is bad and
the coil goes open after it gets warmed up after a bit,
here is what I'd do. Close the gas shut-off valve to the
furnace so no gas can flow. Then jumper 24V direct to
the gas valve for 15 mins. Then remove the jumper, turn
the gas back on and try to start the furnace.

I did this (had to run to the surplus store for a transformer). They
only had a 42V CT, so I got 21V or so, but that was enough for the 24V
solenoid, and if it's a heat problem in the coil then the lower voltage
means higher current so it should heat up even more. The valve opens and
closes just fine. Even after 1/2 hour if I turn on the gas it flows
through the valve. I connected the valve back to the control board and
started the furnace and it started. It ran for about the same amount of
time before the valve closed. Then the same symptom, the 24V goes onto
the terminals of the valve but the it doesn't open.

Perhaps it's a heat related problem.

SMS wrote:
On 11/12/2012 10:45 AM, wrote:

Alternatively, if you suspect the gas valve is bad and
the coil goes open after it gets warmed up after a bit,
here is what I'd do. Close the gas shut-off valve to the
furnace so no gas can flow. Then jumper 24V direct to
the gas valve for 15 mins. Then remove the jumper, turn
the gas back on and try to start the furnace.

I did this (had to run to the surplus store for a transformer). They only
had a 42V CT, so I got 21V or so, but that was enough for the 24V
solenoid, and if it's a heat problem in the coil then the lower voltage
means higher current so it should heat up even more. The valve opens and
closes just fine. Even after 1/2 hour if I turn on the gas it flows
through the valve. I connected the valve back to the control board and
started the furnace and it started. It ran for about the same amount of
time before the valve closed. Then the same symptom, the 24V goes onto
the terminals of the valve but the it doesn't open.

Perhaps it's a heat related problem.

Assuming the filter is clean, I would open all of the registers to insure
the problem is not being caused by reduced air flow causing overheating in
the furnace...

On 11/12/2012 7:57 PM, SMS wrote:
On 11/12/2012 10:45 AM, wrote:

Alternatively, if you suspect the gas valve is bad and
the coil goes open after it gets warmed up after a bit,
here is what I'd do. Close the gas shut-off valve to the
furnace so no gas can flow. Then jumper 24V direct to
the gas valve for 15 mins. Then remove the jumper, turn
the gas back on and try to start the furnace.

I did this (had to run to the surplus store for a transformer). They
only had a 42V CT, so I got 21V or so, but that was enough for the 24V
solenoid, and if it's a heat problem in the coil then the lower voltage
means higher current so it should heat up even more. The valve opens and
closes just fine. Even after 1/2 hour if I turn on the gas it flows
through the valve. I connected the valve back to the control board and
started the furnace and it started. It ran for about the same amount of
time before the valve closed. Then the same symptom, the 24V goes onto
the terminals of the valve but the it doesn't open.

Perhaps it's a heat related problem.

Oh, and even though maybe I shouldn't have done this, after the control
board would no longer open the gas valve I turned on the furnace with
the gas control valve connected to the external transformer, and when
the ignitor came on I plugged it in to open the valve and ignite the
burners. It didn't open and the burners didn't ignite.

On 11/12/2012 8:19 PM, Ned Flanders wrote:
SMS wrote:
On 11/12/2012 10:45 AM, wrote:

Alternatively, if you suspect the gas valve is bad and
the coil goes open after it gets warmed up after a bit,
here is what I'd do. Close the gas shut-off valve to the
furnace so no gas can flow. Then jumper 24V direct to
the gas valve for 15 mins. Then remove the jumper, turn
the gas back on and try to start the furnace.

I did this (had to run to the surplus store for a transformer). They only
had a 42V CT, so I got 21V or so, but that was enough for the 24V
solenoid, and if it's a heat problem in the coil then the lower voltage
means higher current so it should heat up even more. The valve opens and
closes just fine. Even after 1/2 hour if I turn on the gas it flows
through the valve. I connected the valve back to the control board and
started the furnace and it started. It ran for about the same amount of
time before the valve closed. Then the same symptom, the 24V goes onto
the terminals of the valve but the it doesn't open.

Perhaps it's a heat related problem.

Assuming the filter is clean, I would open all of the registers to insure
the problem is not being caused by reduced air flow causing overheating in
the furnace...

I'm pretty sure it is heat related since when the furnace is off and I
apply power to the valve it works just fine and stays open indefinitely.

Early on, I tried running the furnace without the filter for a cycle in
case the filter was the problem (even though it's not dirty) no dice. A
lot of the registers are closed off, but they've been closed for years
without a problem, but I opened them to try that theory--no dice.

When the gas valve doesn't open, I do hear the click of the relay on the
control board, but not the thunk of the solenoid on the valve (and as I
said the valve is getting 24VAC). Even applying 21V directly on the
solenoid (after the hot glow ignitor comes on) doesn't activate the
solenoid.

On Nov 13, 6:19*am, SMS wrote:
On 11/12/2012 8:19 PM, Ned Flanders wrote:





SMS wrote:
On 11/12/2012 10:45 AM, wrote:

Alternatively, if you suspect the gas valve is bad and
the coil goes open after it gets warmed up after a bit,
here is what I'd do. * Close the gas shut-off valve to the
furnace so no gas can flow. * Then jumper 24V direct to
the gas valve for 15 mins. * Then remove the jumper, turn
the gas back on and try to start the furnace.

I did this (had to run to the surplus store for a transformer). They only
had a 42V CT, so I got 21V or so, but that was enough for the 24V
solenoid, and if it's a heat problem in the coil then the lower voltage
means higher current so it should heat up even more. The valve opens and
closes just fine. Even after 1/2 hour if I turn on the gas it flows
through the valve. I connected the valve back to the control board and
started the furnace and it started. It ran for about the same amount of
time before the valve closed. Then the same symptom, the 24V goes onto
the terminals of the valve but the it doesn't open.

Perhaps it's a heat related problem.

Assuming the filter is clean, I would open all of the registers to insure
the problem is not being caused by reduced air flow causing overheating in
the furnace...

I'm pretty sure it is heat related since when the furnace is off and I
apply power to the valve it works just fine and stays open indefinitely.

Early on, I tried running the furnace without the filter for a cycle in
case the filter was the problem (even though it's not dirty) no dice. A
lot of the registers are closed off, but they've been closed for years
without a problem, but I opened them to try that theory--no dice.

When the gas valve doesn't open, I do hear the click of the relay on the
control board, but not the thunk of the solenoid on the valve (and as I
said the valve is getting 24VAC). Even applying 21V directly on the
solenoid (after the hot glow ignitor comes on) doesn't activate the
solenoid.- Hide quoted text -

- Show quoted text -

Well from the above it would seem very clear to me.
You have a bad gas valve. At times, it won't open or
stay open with 24V directly on it. You've seen that with
the votage applied both from the furnace control board
and from your seperate experimental transformer.
Has 24V and won't open = bad gas valve. And you know
it's an opening issue at the valve, not a gas supply
problem, because you say you also don't here the normal
"thunk" sound of it opening.

On 11/13/2012 4:58 AM, wrote:

Well from the above it would seem very clear to me.
You have a bad gas valve. At times, it won't open or
stay open with 24V directly on it. You've seen that with
the votage applied both from the furnace control board
and from your seperate experimental transformer.
Has 24V and won't open = bad gas valve. And you know
it's an opening issue at the valve, not a gas supply
problem, because you say you also don't here the normal
"thunk" sound of it opening.

I hate intermittent problems.

SMS wrote:
The electric ignitor always starts up correctly (it's not a spark
igniter, it's more like a glow plug).

Sometimes the solenoid for the the gas valve opens and the burners
ignite the main blower comes on and it works fine for about five
minutes.
Even when this all works properly, after about five minutes of heating
the burners go out, then the controller tries four times to light
them.
When the burners go out, the 24V on the gas valve connections goes
away so the gas valve closes. But when the controller tries to
restart the burners, the ingiter does come on, then there is 24V on
the gas valve, but the gas valve doesn't open (at least I don't smell
gas) and the burners don't ignite.

What is it that is tripping and thinking that the gas needs to be shut
down in the first place? Why doesn't the gas turn back on when the 24V
is on the gas valve terminals?

I don't think it's the flame sensor, because the gas should come on
when the burners try to be ignited then the controller only turns off
the gas if the flame sensor doesn't detect a flame.

The draft inducer motor runs fine, and pulling off the hose, there is
air coming out. I bypassed the pressure sensing switch (you have to
have in open in order for the system to start, then closed once the
draft inducer is running) to see if it was failing, and even with it
bypassed the gas still shuts off long before the thermostat
temperature is reached.
I bypassed the three firebox flame-out sensors (one by one) and it
didn't help (I did not try bypassing all three at a time).

Any ideas? I would say it's the gas valve but since it works fine, one
time, I wonder how likely intermittent operation is.

The flashing trouble code LED just indicates "fail to ignite," and
indicates that the trouble could be the gas valve, the gas pressure
from the supply, or the flame sensor.

It's an old Sears Furnace, probably 25 years old. I can't find the
model number anywhere. The gas valve is a White-Rodgers 36E36 227.
How hard is it to replace these. It looks like just removing the
pipes from the gas supply and the manifold. I'm just worried about
damaging the manifold if it's really tight.

I wonder if it is the electric ignitor that is the problem, even though the
ignitor glows and appears to be working.

The reason that I wonder about that is that I had a similar problem with a
gas oven that wouldn't heat up. The ignitor appeared to be working because
it glowed when the oven was turned on. I did some Google searching and
learned that even though the ignitor was glowing, it still could be the
cause of the problem. At least with a gas oven, the ignitor has to allow a
certain amount of current to go through before the gas valve will open up so
the oven can be ignited. If a gas furnace has a similar setup (I don't know
if it does), then maybe the ignitor is the problem -- despite any voltage
readings that you may be getting. Apparently, it is not just voltage (in
the case of a gas oven), but it also requires a certain amount of current
(amperage) to be drawn before the gas valve will open or open fully.

Here are two links about that in regard to gas ovens:
http://www.applianceblog.com/mainfor...ont-light.html



http://www.youtube.com/watch?v=zkV4Wj0klkQ



Again, I don't know if a gas oven and a gas furnace have a similar setup,
but I thought I'd pass this on in case it helps.



I also just tried a little Google search regarding furnace ignitors and this
link has a post by "Kokomo" that says the only way to test the furnace
ignitor is by measuring the current (amperage) draw:



http://www.doityourself.com/forum/ga...e-igniter.html .



Good luck and let us know what the problem turns out to be.

On Tue, 13 Nov 2012 18:06:11 -0500, "TomR" wrote:



Again, I don't know if a gas oven and a gas furnace have a similar setup,
but I thought I'd pass this on in case it helps.

My furnace looks for inducer negative pressure and ignitor glow before
the gas valve opens. Then good flame sensor sensing keeps it open if
flame is present.
I've replaced an inducer pressure switch for no purpose at all. You
can hear the switch close, and if the ignitor glows, it's okay.
Mine is timed for about 30 seconds before the ignitor glows.
I don't know how "glow" is detected by the circuitry, but I do know no
glow, no gas valve open, because I've replaced an ignitor that didn't
glow. Gas valve never opened.. But maybe there's other failure modes.
And I know a bad/dirty/flaky flame sensor can shut the gas valve.
Seen that happen too. Always immediately after flame ignition in my
case.
Pretty sure the gas valve has 2 steps. Low volume during the flame
sensor check, then high volume and main blower kicks on.
Been about 5 years since I've had a problem and actually looked at it.
This is all start-up ciruit logic, and I have no idea about logic in
effect during running operation.
AFAIK my roll-out sensors have never been tested, so I don't know if
they work.
A good manual for the controls should tell you all this. I also have
schematics in the furnace case, but don't know how to read them.
I'm an electricity know-nothing.
My furnace manual came with about 5 different possible control
setups, so you have to get that right first.
There's control board logic circuitry that can get messed up just like
an automobile ECU.
If you're guessing and confused, a pro will fix you up.

On Nov 13, 8:59*am, SMS wrote:
On 11/13/2012 4:58 AM, wrote:

Well from the above it would seem very clear to me.
You have a bad gas valve. *At times, it won't open or
stay open with 24V directly on it. * You've seen that with
the votage applied both from the furnace control board
and from your seperate experimental transformer.
Has 24V and won't open = bad gas valve. *And you know
it's an opening issue at the valve, not a gas supply
problem, *because you say you also don't here the normal
"thunk" sound of it opening.

I hate intermittent problems.

if you apply THE CORRECT voltage directly to the valve coil and it
doesn't open, it's bad..

check it with an Ohm meter, the coil could be open intermittently

or there could be an intermittent short from the coil to the frame
which might mess up the controller but not mess up your external test
power source

or the valve could stick mechanically in which case you won't see any
problem with electrical tests

you're not in Indianapolis by any chance?

Mark

why does no one ever effing post when they have found the solution?!