Hello
I have a Tempstar/Keeprite furnace model HGF120NE-1, Serial number 8464124770. (the exterior of the furnace has Tempstar logo and interior of furnace has Keeprite logo.)
This furnace has an intermittent pilot light system.

At times, especially in the morning after allowing a temperature drop over night, the furnace will not function. If I switch the "emergency furnace switch" off and then on again, the pilot light ignition begins, the pilot lights and then the main burners and the furnace functions as normal. Sometimes the furnace will continue normal operation until the next evening cool down period. Sometimes the furnace will need another "manual" start with the "furnace switch" to function normally. It acts like the furnace is "locked out" and the off/on procedure with the "furnace switch" is resetting the furnace, at least for that cycle.

I believe I eliminated the thermostat as a possible problem as I have a backup non-digital thermostat installed about 10 years ago. (We get -40 degree temperatures so a backup thermostat without batteries gives some degree of safety) I removed the digital thermostat and the results with the old style thermostat were identical. I also replaced the "emergency furnace switch" just to make certain that it was not an issue.

The malfunctions are, of course, happening more often.

Does your furnace vent with plastic or metal pipe?

It vents with metal pipe. It is an older furnace. It does have the intermittent pilot system but does not have the evacuation fan (induced draft furnace) of most mid efficient furnaces. Strange.

Have you cleaned the flame sencer or t-couple lots of times on the tempstars the piloit will spark and light but will never sense the flame to turn on the main burner

I will do that today, but the problem appears to exist before the flame sensor would come into play. (I think) When it works correctly the high voltage pilot ignitor buzzes, the pilot light lights then the burners and then the fan. When it malfunctions, the ignitor does not even buzz to light the pilot light. Therefore the flame sensor has nothing to sense. Could the flame sensor have anything to do with the ignitor before the pilot light is lit?

No if that is the case I would say the gray spark box is going bad, not sending power to the ignitor.

Thanks Joshdta
That very well may be the problem. I just find it strange that I can reset the furnace by shutting off the power and then returning power. So far, this works every time and the furnace pilot ignites almost instantly. I wonder if there is a relay in that spark box that gets stuck in a certain state and when I shut the power down, returns to the correct state? (either open or closed)

There probably is I am checking it right now. Do you have the number of your spark box?

The box is a:

Honeywell, S86H INTERMITTENT PILOT
100% SHUTOFF
AUTO IGNITION
SYSTEMS ANS Z21.20

24 V, 60 HZ
AMP=PV+MV+.2A
PV=2A MAX
MV=2A MAX

TH CURRENT = PV + MV + .2

90 SEC. MAX. TRIAL FOR PILOT IGN.

The furnace itself, I believe, is really a Keeprite and manufactured in Canada.
Thanks Again

If you are sure that half the time the sparker will not spark then it is almost certain the box which will have up to 3 relays in it.

I found some specs on the box. I am now wondering if it could be the ground from the SH6H box?
http://customer.honeywell.com/Techli...0s/69-0166.pdf

The following is from that article. I am thinking if the grounding for the ignitor is faulty, is sounds like the unit goes into lockout. I think you have pointed me in the right direction. Of course the darn thing wouldn't fail all afternoon. I am going to pull off the ground right at the ignitor and clean it up.
CHECKING GOUNDING
A common ground is required for the pilot burner/
Igniter-sensor mounting bracket and the GND terminal
01 the 586. If ground is poor or erratic. Safety Shutdown
May occur occasionally even though operation is
Normal at the time of the checkout. Therefore. If
Nuisance Shutdowns have been reported, be sure to
Check item 4 under General Precautions. Page 1.
NOTE: If the ground circuit path is incomplete, the
S86G and H will allow one trial for ignition before
Going into safety lockout.

A bad ground could very well be the problem, defentally check that first before buying a new box

If it is the ground, once I clean it up, the furnace should function normally this evening and tomorrow morning after the overnight setback temperature. I will let you know the outcome tomorrow.

If it still is acting up, I will look at replacing the box.

Thanks Again.

Sounds like you just about got it fixed then. Glad I could be of some help. Have a great day. Let me know what you find out!!

Yesterday, I checked and cleaned the grounds, and carefully cleaned the ignitor. The ignitor tip actually looked very good before I cleaned it.
The furnace ran flawlessly last night and today so far. I have my fingers crossed that it will continue this way. From the way this winter has been, I think I still have at least 3 months of heating left before summer. (I wish that last statement was a joke)
Thanks for all your help Joshdta. It is much appreciated.

No problem glad you got it working!