Greetings,

I have a Nordyne gas furnace model CMF 80 PG CONV. This unit has a controller box made by United Technologies (1018 series hot surface ignition). When the thermostat calls for heat:
1. the burner motor turns on
2. the hot surface igniter turns on
3. the gas valve opens and the flame lights
4. the blower eventually turns on
5. warm air circulates the house for about 15 minutes
6. the gas valve shuts off even though there is still a call for heat from the thermostat
7. the blower fan runs for about 5 minutes and shuts off
8. the controller box blinks the led a sequence of 2 flashes

if I turn off the heat call from the thermostat and then back on again, the controller box stops flashing and the process above repeats, but the flame doesn't appear to stay on for more than 5 minutes the second time around. When starting from cold, the flame stays on longer.
This unit recently had a new heat sensor igniter and a new controller box installed. Previously, it would keep the flame on only for a few seconds and give a 3 flash error code. With new HSI and controller box it stays on longer but when it fails, it flashes twice.

Can anyone help me with this? I would appreciate a link to an error code chart.
Best regards,
Unidentified

 

Give it a go...report back if you can't figure it out.
https://www.manualslib.com/manual/90...Pg.html#manual

 

Hi 57TinkerMan,

thank you for the link! The sequence of events I observe in my furnace is the same as described on page 22 of the manual you shared with me. The problem starts after about 15 minutes continuously operating, when suddenly the burner motor stops working. According to the manual, the burner motor is controlled by the voltage on the "W" terminal from the controller box. The manual says that 24V to "W" will lead to the energizing of the burner motor.

Coupled to the burner motor is also a centrifugal switch, which is activated by the spinning of the motor. This centrifugal switch is covered by an end cap. I am assuming this switch is working, because the burner motor spins, and the sequence progresses to the energizing of the heat surface igniter.

Why would the burner motor stop after 15 minutes of operation even though there is a call for heat from the thermostat? Does that mean that the voltage to terminal "W" is dropping from 24V to zero?

I am wondering whether the burner motor is worn out. Or is the centrifugal switch worn out. Could the motor start losing speed after it warms up, leading to opening the centrifugal switch?

The two flashes error code means: "the control is in lockout because the signal was not received by the control that the inducer centrifugal switch had closed within the time".

I am not sure where to look next. Do you have any ideas? I appreciate your time going over what I wrote.

 

The draft inducer has to run to prove the centrifugal switch. If the inducer doesn't run.... the switch will not prove and you will get that code.

Set your meter for 24vAC and check from C to W for 24vAC. If that drops out then it's a thermostat problem. If that stays normal and the inducer stops it points to the control.

Your problem sounds more like the furnace is overheating. The manual shows a receptacle where the burner section plugs in. There must always be 120vAC at the receptacle. If there is not..... you have a safety limit opening.

 

Hi PJmax and 57TinkerMan,

You are correct about the overheating issue.

While troubleshooting my furnace problem with a salesclerk in my local hardware store today,
he pickedup that he furnace is overheating because the house is totally cold (35F).
The furnace cannot satisfy the thermostat quickly enough, so the furnace heats up and the safety limit is triggered, cutting off the power to the draft motor, leading to shut off of gas valve.
I tested his theory by running the furnace in alternating intervals of 5 minutes ON and 5 minutes OFF for 1 hour today. The furnace never went into lock out.

I greatly appreciate that you both took the time to read what I wrote and replied back! The manual was really helpful. I feel I learned something valuable by going through this troubleshoot. I can certainly say that now I understand better how my furnace works. It always intimidated me before.

I wish you both success on any projects your are currently working on.

 

You don't mention if this is your first winter with this furnace, but I assume it's not and the furnace has worked fine in the past. A couple of easy things to check first before digging into the furnace itself. If it's tripping out on high bonnet temperature (overheat), I assume you've checked to make sure the filter is relatively clean. Have you closed off a large number of heat registers, trying to avoid heating unused rooms? Do you have central AC installed on this furnace? If you do, you might try setting the blower switch at the thermostat to continuous on. With AC installations, this usually kicks the blower up to a higher speed and might increase the air flow enough to either allow for a longer heating cycle, or perhaps totally avoid tripping out on overheat. If this does the trick, you may need to change the blower speed to a higher setting. Just some things to check in order to get you through the holiday without freezing things up.

 

That furnace is made for use with package A/C only. Setting the stat to "fan on" would likely run the fan on the package A/C, if it did anything at all. Beachboy makes a couple of good points regarding the filter & closed registers. I would add, to check the fan to ensure the blades are clean. Even with long runs, the furnace shouldn't be overheating.