Furnace burners won't ignite

[rocketman]

I have an Amana GHN90A50 furnace (circa 1987) that has an ignition problem: I will occasionally notice the house is cold, with the temp well below the setting on the thermostat. When I check the furnace, the blower is running, the ignitor is glowing but no ignition. If I then set the thermostat lower than the room temp, the blower and ignitor shut off. I wait a few seconds (which I guess allows the furnace to reset) and raise the temp on the thermostat. Then everything is fine: the blower and ignitor come on and the burners ignite.

I have a suspicion that this only happens (and then, only occasionally) when we set the thermostat low for the night (60 or 61 degrees) but I have not tested this theory. Strangely, our tenants in a house we rent had the same problem with a new furnace we installed there a year ago; they set it low (maybe 55 degrees) because they were out for a few days and found that the furnace didn't ignite.

Any suggestions?

[Mikepier]

Wierd, usually the blower should not come on unless the chamber or duct reaches a certain temp. Sounds like something faulty with the circuit or control board.

[Ken]

I do not know what tools you have or what your capabilities are, but I would hang a volt meter across the valve coil terminals to see if the

24v AC is being applied when heat was being called for. That will tell you much about your problem.

[rocketman]

The furnace is running right now and I just checked the coil: yes, it's got 24v across it (obviously, since it's working). The next time the furnace won't light I'll re-check the coil. So let's say it has no or low voltage then, what's the likely culprit?

[hallerb]

sounds like a bad ignitor, when the last time the furnace was serviced?

[Mikepier]

These are all valid suggestions for troubleshooting, but I'm still puzzled why the blower comes on if there is no flame?

[Ken]

You need to back up to where the 24v comes from. It probably is going to a control board, but you must follow the leads. Such a problem could be as simple as a poor connection.

If the voltage IS there at the valve and it fails to open, it could well be a bad valve. I have had a couple valves where the coil winding on the valve opened up causing such a problem. You can check for such a problem by removing one of the wires going there and measuring the coil resistance with an ohm meter. Keep in mind however that your connection could be intermittent. Hang the ohm meter leads securely across the coil and tap the valve with the handle of a screwdriver. If it momentarily opens up, that is your problem.

[hallerb]

burner likely turns on, then off quickly

[clare]

NOT likely to be a bad ignitor, as it is glowing, trying to light gas that, apparently, is not there.

[clare]

Either that or the controller starts the fan after a fixed delay any time the burner is "turned on " (whether actually burning or not) as a fail-safe to protect against a high-limit failure.

[Don Young]

I thought maybe the OP was referring to the draft inducer rather than the main blower. Or maybe the control is in a lockout mode which runs the main blower.

Don Young

[daszkiew2000]

pull flame sensor ( turn thermostat down first or turn the heat totally off, then unplug flame sensor lead from control board, unscrew sensor) then clean it with steel wool - it worked for me few days ago :)

[rocketman]

.

I'll try this. But What are you saying is wrong? That the flame sensor is somehow keeping the valve from opening and letting gas flow?

[rocketman]

I think it is the main blower that is running. What might cause the controller to go into lockout mode?

[Mikepier]

.

I thought lockout mode shuts down everything, including the blower, and must be reset manually.

[Don Young]

I think it is the main blower that is running. What might cause the controller to go into lockout mode?

The control board generally has a light which blinks a code indicating the reason for the lockout. Controls go into lockout and require manual reset when an unsafe condition is recognized. Often the control will retry several times before locking out. The main blower might be left running if the lockout was due to an over-temperature condition during the last cycle.

Don Young

[Tony Hwang]

Hi, If blower keeps running high limit sensor opened and not closing even after cooling. I just had that problem last week. high limit switch was open and never closed even after cooling down. As a result blowr was running on and on. I removed sensor and gently tapped it and it closed. I ordered a replacement but since furnace has been running OK. As simple as dirty filter can trigger high limit sensor.

[Stormin Mormon]

Some furnace, the blower comes on a certain time after the burner. Other furnace, the blower comes on based on the temperature of the heat exchanger.

[pabas]

pabas had written this in response to

:

Did the answer posted > >> > I have an Amana GHN90A50 furnace (circa 1987) that has an

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