rocketman wrote:
On Jan 21, 8:13 am, Ken wrote:
rocketman wrote:
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?
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.

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?

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.