I have 2x Tempstar Heil NTxx series units (both about 15 yrs old) (dual zone home).
Both units are installed horizontally in the crawl space. Natural Gas. System also has 2x AC compressors.
Up until now, both units have performed well.
On one of the units, I'm noticing the following behavior (note that for the last year, this problem was intermittent. Now it is permanently not working).
(Note that I had posted this intermittent problem last spring, but my description of the behaviors and terminology was not all that accurate).
Better Description of the problem.
(the fan setting on the thermostat is set to "AUTO").
BTW, I'm not 100% sure this is the sequence of events but here is what I think is happening.
1. When calling for Heat, the Squirrel fan kicks on and runs (safety / clear flu / positive ventilation).
2. There is a diaphragm/switch which senses the flue is safe/ready, and signals the ignitor to switch on/glow?? and the gas valve to switch on.
3. After the expected delay (time running the Squirrel fan (est 60 seconds), there is NO glow on the ignitor and NO clicking from the gas valve.
4. I swapped the diaphragm/switches from the two units (good one and problematic one) and the problem did not 'move'. Therefore I'm assuming the diaphragm/switch is not my problem. (they are the same WF) I also verified that there is no obstructions or debris in the vent to the roof.
5. ... the Squirrel fan will continue to run until I turn off unit (Don't call for heat).
I'm looking for any tips on next steps. Getting to my units is challenging. Therefore I'd like my trips in the attic to be productive.
Check volts on the ignitor?
Check volts on Gas Valve?
Tap Gas Valve with a hammer?