12 replies to this topic

[seitz]

the furnace seems to be ok other than no gas flow. the igniter works,blower works, all is well but do gas flow through new valve. i put a new valve on because the inside panel said it was one of 4 things, gas pressure,gas flow, flame sensor, or the valve. since i have gas to the valve i assumed it was the valve. it cant be the flame sensor as it will not fire. help!!

[Dan Webster]

What I would do is remove the wires from the gas valve and fire that puppy off. Check if any voltage is gettin to the valve. The board won't be sending any voltage due to multiple factors. Bad board (fuse) or Bad limit(s) being the first thing I would check.
Sequence of events in the life of a draft induced high efficiency furnace:

Edited by applianceman18007260692, 14 December 2011 - 10:26 PM.

[Bobice]

Try this, also applies to furnaces and boilers. http://www.americanw...guides/fvir.pdf

[Bobice]

Gas Furnace Components – Gas Valve Troubleshooting



Multi-Meter used sometimes for Gas Valve Troubleshooting

Only qualified gas furnace technicians should troubleshoot gas furnace problems

Gas valves used in modern state of the art gas heating units are typically controlled via a state of the art electronic ignition control or a printed circuit board. Other types of gas valves include the standing pilot gas valve. Gas valves can be found on gas furnaces, gas fired steam or hot water boilers, and gas fired water heaters. When troubleshooting a gas valve the technician should only be concerned with input to the gas valve and output of the gas valve whether it is an electronically or circuit board controlled gas valve or a standing pilot gas valve. If something is wrong with the internal components of the gas valve the gas valve should be replaced and not repaired in the field. Only the gas valve manufacturer or someone certified by the manufacturer of the gas valve can make repairs and certify the safety of the gas valve. This also applies to gas valves that have been submerged under water due to flooding of your boiler or gas furnace or water heater.. The rule is if the gas valve is found to be defective internally in any way or has been submerged or partially submerged change it out for a new gas valve.

[jumptrout]

Check for continuity through the pressure switch and check for power at the gas valve.

[Dan Webster]

It is not rocket science. And as far as replacing a gas valve, test for leaks with soap bubbles before you fire that puppy off. Make some photos of your gas valve your pilot and you burners so we can know what you have. Ain't no way to look up sh!t fer HVAC on line

Edited by applianceman18007260692, 15 December 2011 - 11:16 PM.

[RegUS_PatOff]

from some GMPN series info,
a few things will prevent power to the Gas Valve:

PRESSURE SWITCH
(4) ROLLOUT SWITCHES
STACK OVERTEMP SWITCH

VENT PRESSURE SWITCH
This furnace utilizes a vent pressure switch which prevents the furnace from operating should any
portion of the vent system become restricted or a venter failure occur.
To check this switch, place the furnace in operation and remove the hose from the switch.
The gas burners will extinguish.
Replacing the hose will allow the furnace to operate normally.

FLAME ROLL-OUT SWITCH
This furnace is equipped with four (4) flame roll-out switches.
These manually resetable switches are 1/2” disc type and are non-adjustable.
They are designed to shut down the burner gas in the event that flames are detected outside the heat exchanger.
Should a switch function, contact a qualified service person to determine the cause of function before resetting.
To reset this switch press the button on top of the switch after the furnace has cooled.
To test the operation of the switch with the furnace in operation, place an open flame on the disc portion of the switch.
The switch should function to shut down the burner gas.
Wait until the furnace has cooled sufficiently before resetting the switch.

STACK OVER-TEMPERATURE SWITCH
Located on the venter blower housing, this switch is designed to shut down the burners should the
circulating air blower fail or the secondary coil become blocked.
To test this switch, bypass the main limit switch, disconnect the circulating air blower, and place the furnace in operation.
After a short period of time this switch should function shutting down the burners.
IT IS VERY IMPORTANT TO REMOVE THE BYPASS FROM THE MAIN LIMIT SWITCH
AND REPLACE THE WIRES WHICH WERE DISCONNECTED FOR THIS TEST
PRIOR TO RETURNING THE FURNACE IN NORMAL OPERATION.

[Dan Webster]

Good info Reg. I have these in my notes also:


A sampling of various failure codes on a furnace:

Read one LED flash that stays on continuously to mean your furnace has no signal coming from the thermostat and will not operate. Turn the power off and check the thermostat for improper settings or connections.

Interpret one LED flash that blinks on and off to mean your furnace has locked out because it could not ignite after three tries, and must be reset. Interrupt power to your furnace for 20 seconds or lower the thermostat so your furnace does not try to heat, then reset the thermostat to the previous setting. After one hour of lockout, your furnace will automatically reset itself and try to operate as usual.

Decipher two LED flashes to mean the draft blower is not working, or your furnace has a short in the pressure switch circuit. Turn off the furnace power and repair a short or replace the pressure switch.


Read three LED flashes to mean your furnace has an open pressure switch circuit or it has an induced draft blower operating. Check the pressure switch hose of your furnace for blocks or an improper connection. Also, look for blockages in the flue, and tighten any loose wiring.

Translate four LED flashes to mean your furnace has a primary limit circuit open, possibly from loose wiring or blocked filters. Check and clean filters, tighten wiring and check the flue for blockages.

Interpret five LED flashes to mean your furnace senses a flame without a call for heat. This could be from a gas valve closing slowly or a burner flame lingering.



Read seven LED flashes as a warning of a low flame sense microamp signal. This could happen with a coated flame sensor or a lazy flame from poor gas pressure. Turn off the power and adjust the gas pressure according to the information on the rating plate.



See eight LED flashes as meaning an igniter circuit problem due to a bad igniter or an igniter connected improperly. Replace the bad igniter or check the ground wiring, making necessary corrections.



Decipher nine LED flashes to mean the high-stage pressure switch circuit will not close during a high-stage-induced draft blower operation. Your furnace may have a pinched or blocked pressure switch hose, a blocked flue or loose wiring.

Read continuous flashing on the LED to mean your furnace has a reversed polarity of 115 volts. Turn off the power and correct the wiring polarity after reviewing the wiring diagram.

[jumptrout]

Check for continuity through the pressure switch and check for power at the gas valve.

Useful information has been provided but you are not firing the ignitor. Check your pressure switch and power to the gas valve. If they prove OK,we will go to the next step.

[Shootist]

The GMPs are pretty straightforward. If the ignitor is glowing but the gas valve is not opening then there's nothing wrong with the pressure switch or the flame sensor. I think you will find that one of the three roll out sensors is tripped as they directly break the 24v signal to the gas valve. These little sensors usually have purple connecting wires looping them together with the gas valve. They have a little square button sticking up in the center that will make a click if you press down on it when it is tripped.
Here's the deal.....these roll out sensors are there to detect a problem with the integrity of the heat exchanger. The reason there are 3 is because the GMP can be installed 3 ways. Upright, horizontal blowing left or horizontal blowing right. The most important sensor is the one on top depending on how the furnace is installed. Check the top-most sensor first and see if it is tripped. If it clicks when you press on it then try the furnace again. Now, this part is very important! If the burners now fire up carfully watch how the jets of fire are sucked into the exchanger tubes by the draft inducer fan assembly. After about 20 seconds the main blower should kick on. Carefully watch for any change in how deeply the fire is being sucked into the tubes. If one of the exchanger tubes is cracked the fire will appear to roll back out of the tube a little once the main blower kicks on. if this happens the exchanger is toast. If not then the sensor is probably just weak. The weak sensor can be swapped with one on the very bottom if horizontal or one of the sides if upright. If none of the sensors appear tripped then next take a volt meter and check for 24v to the gas valve about 5-10 seconds after the ignitor starts to glow. if you're getting 24v then there's something wrong with the valve (installed backwards?). If still no 24v to the valve then check the 3 roll-out sensors for continuity. If all else fails take the blower door off and use some heavy tape to hold down the door switch. On the GMP you may need to remove the rectangular silver cover from in front of the control board so you can actually see the red LED diagnostic light. Turn the heat on with the door off and let it go. Some error codes won't appear until after it has 3 ignition failures in a row and the furnace locks out. I think the GMP only has 5 or 6 different codes; just count the number of blinks.

[RegUS_PatOff]

... no gas flow.
... the igniter works,
... blower works,

... If the ignitor is glowing but the gas valve is not opening then there's nothing wrong with the pressure switch or the flame sensor.

GMPN wiring diagram

[Shootist]

Oops. I overlooked the "N" in the model number. I've only seen one GMPN in my career; we don't sell many 90+ furnaces here and most people looking for 90+ furnaces aren't shopping Goodman .
Looking at your schematic; the pressure switch does appear to break the 24v to the gas valve in the GMPN. However, if the pressure switch was failing to close there would be a flash code and the ignition sequence would stop. So If the pressure switch doesn't close there's no way the sequence progresses to the ignitor glowing. However, the more I look at that low-voltage wiring diagram the less it makes sense. The pressure switch is shown as "normally open" (as it should be). All the other sensors are obviously "normally closed" and in a continuous loop with the pressure switch and gas valve. Now, if one of the roll out sensors were tripped open the control board would not see the pressure switch closing and would give a flash code of "3" and a false error code of "pressure switch failed to close". Also, according to this diagram when the thermostat calls for heat 24v is sent from "W" on the thermostat directly to the gas valve after passing through the pressure switch and roll-out sensors. That would mean that the main gas valve would open the moment the pressure switch closes (and stay open as long as the pressure switch stays closed). We all know that's not how things work. The moral of the story is that Goodman's wiring diagram is pretty much worthless in troubleshooting a low voltage wiring issue.

Maybe this will help with the troubleshooting:

HEATING MODE
· The furnace control checks for an open main limit (this limit is in the normally closed ). If the
limit is open, the furnace will remain inoperable until the limit is closed. During an open limit
the circulating air blower will be energized. The status light will blink four (4) times.
· The room thermostat reacts to a demand for heat.
· The control will then check to insure that the vent pressure switch is open. If, at this point, the
vent pressure switch is closed the control will blink two (2) times and will remain inoperable
until this situation is corrected.
· The venter blower is energized.
IO-151 19
· The vent pressure switch will close when it detects a pressure in excess of it’s setting. If the
pressure switch fails to close the status light will flash three (3) times. The sequence cannot
continue until the pressure switch closes.
· The flame rollout switches are then checked to assure that they are in the closed position.
· After a pre-purge of about fifteen (15) seconds the electronic ignition device will be energized.
· After a slight delay the gas valve will open if the flame rollout swithches are closed.
· The burners will ignite and the flame sensor will detect the presence of flame. The ignition
device will deenergize. If the sensor does not detect the burner flame, the gas valve will close
and the ignition cycle will be repeated for a total of three attempts. If, after the third attempt,
the presence of flame is not detected, the furnace will go into a lockout condition for one (1)
hour. It will then repeat the ignition cycle. This one (1) hour lockout and retry will occur
indefinitely.
· Thirty (30) seconds after the main valve is energized the circulating air blower will be activated.
· The furnace will remain in operation until the demand for heat is satisfied.
· Once the demand is satisfied the venter will shut off, and the circulating air blower will shut off
after the field selectable time off is attained.
· The furnace will remain dormant until the next demand for heat.

I'm still leaning toward one of the roll-out sensors breaking 24v to the valve. With the exception of a defective or improperly installed gas valve or a bad control board the roll out sensors are about the only thing that would keep the gas valve from opening but not give an error code.

Edited by Shootist, 04 January 2012 - 11:10 PM.

[jumptrout]

Did you get this furnace working?