Gas Furnace

will smith_4

If the entire unit shutdown on you, I wouldn't suspect a limit. When a high temp limit opens, the burner will shut off, but the blower will (or rather, should) continue to run.
I'd disconnect the wiring from the stat at the circuit board, jump out the heat circuit to call for heat, then watch what happens. If it does the exact thing, I'd be inclined to think the board is faulty. Do check the temp rise across the furnace and compare it to the unit's allowed rating, and check to see what the blower's timed on and off settings are. (Most boards will have adjustable timing switches)

Jesse Markeveys

Brand new condensing gas furnace

I was installing a condensing gas furnace and I had it all set up and ready to go. I went to turn it on and it first turned on the inducer motor prooved continuity through all of the switches and then energized the hot surface ignition. Next it called that gas valve and then when it got up to temp it called the indoor blower motor. The flame would stay lit for somtimes 2,5 or even 10 minutes then it would cut voltage to the gas valve run the inducer for thirty seconds and then the fan would run for about two minutes untill the de-energizing relay would open. It does this continuoslly and I don't know what to do. I have checked all that I could. It is not off on high limit, the pressure switch is not open when it should be closed and the circut board is not bad (I already replaced it) There is a 20 deg. delta t across the return and supply that seems adiquite. I do not know what else to check for. I am in the process of finding the make and model of the furnace (It is not mine and there is no nomenclature on the front) Thank you all for your time I am sorry for any problems with detail that I have not shown in the past. I am out of ideas. Jesse Markevey

jim lockard

sounds like

your furnace hit the high limit. I would start there. Did you replace the A/C coil? Maybe that its dirt loaded? Are all the vents open? Start a troubleshoot and find out what switch is open, touch every connection make sure its tight and right. Once you get it going check the temp rise thru the furnace. Did you size the furnace to the existing duct work? what was the size of the old furnace? A little more detail would, help make and model?

Timco

Does the furnace give you an error code? After a failure, the circuit board usually flashes a code, and on the door to the blower or access door there should be a list of what the codes mean and how to read them. Fast & slow pulses / flashes.

Sounds like a limit switch...Clean filter? Air restriction? A high limit switch would do that. Make? Model? The entire unit shuts down?

Tim

A.J.

Check your pressure

That is your pressure at your pressure switch? It needs to be higher than the rating on the switch cut out. If it isn't then maybe your equivalent lent is to much on your vent pipe.

jim lockard

Be nice

to know the make and model. If it is a venting problem (and not sure it is ) pull the flue and see if it will burn? Best Wishes J.Lockard

Ken D.

furnace

Check to see if the condensate is draining properly. It could be backing up, causing the conditions you mention. Also check to see if the ductwork is adequate which could also cause same.

Jeff Lawrence_25

Where'd you get it?

Installing and servicing a furnace is not for a weekend worker. We go through a lot of training to be able to ensure the safety of our customers.

You may need to get a technician to look at it.

Good luck.

tim smith

furnace problems

By the message I can't tell if the main burner is coming on or not, if not then I would suspect a poor or missing ground causing flame failure. Just a thought, Tim.

jim lockard

Jesse

Until you provide some details on the product your wasting everyones time. J.Lockard

Richard_12

Furnace

Check the static pressure, Check gas pressure, Check delta T.
Check pressure switch install a tee in line at pressure switch to check vac.

John Starcher_4

20 degree delta t?

That sounds pretty low to me. The nameplate should list the acceptable delta T range. I would double check your temperatures, and use the same thermometer (preferably a thermocouple type) for the discharge temperature as you do for the inlet air temperature.

Starch

Larry F

heat anticipator?

Have you had a voltmeter across w and c when the furnace cuts out? After re-reading your symptoms it sounds to me like the t-stat is ending the call for heat, in other words, the way you describe the shutdown, it sounds like the furnace is going through its normal cycle after the t-stat satifies (inducer post-purge, blower control timing out to scavenge the remaining usable btu's). The stat heat anticipator could easily cause this condition if not set correctly. If it was the culprit, the stat should call for heat again after a few minutes of cool down and go through the short-cycle over and over. Need to check amp draw in the t-stat circuit and verify the anticipator is set accordingly.

Larry

Jim Bennett

Hi Limit

I remember one a few years back that acted in a similar way. Low delta T, but going off on high limit.It had the limit switch improperly installed (factory)so it was actually touching the side of the heat exchange