Hope someone can spot what I've missed. The issue started after igniter replacement. When the gas valve turns on, sometimes ignition occurs, sometimes not. Ignition may fail on a first or 2nd strike, then ignite on the 3rd. Other times the furnace trips out. When I reset the controls, same thing repeats. In effort to resolve, have confirmed the igniter is properly positioned, confirmed that safety circuits and sequencing are correct. Confirmed gas manifold pressure is correct (3.57 WC). Burners and manifold were removed and fully cleaned (including orifices). When the unit is attempting to start, It seems as if an inverse air current may be sometimes preventing gas from flowing though the burner tube to the igniter. If I "help" the gas flow by blowing gently toward the burner tube (toward the igniter) as the gas turns on, ignition occurs perfectly every time. It seems that gently blowing air in the correct direction allows the gas to overcome whatever may otherwise prevent it from passing correctly through the tube. Since it's a high efficiency furnace with enclosed burner box, I can't imagine where the spurious airflow may be originate (or is it an incorrect diagnosis?)

Hey all - I've got a Tempstar DC90 with a Honeywell Wifi thermostat that doesn't run on batteries. In the middle of the night, I went to change our temp but the thermostat was completely blank / off. FYI: my wife had changed the temp about an hour before that. Realized I had a problem. Here are my symptoms: 1. Blank thermostat - i.e. it's not getting power - verified with multimeter 2. Furnace blowing cool air - not cold, not warm but cool - even though it would normally blow warm air. Here is what I've done so far: 1. Checked AC voltage at the thermostat - It came back 0 - which made sense based on no power to thermostat 2. Checked if there was voltage on the board in the furnace that connects directly to the thermostat. I was getting 0 volts AC. I made sure the door button was pushed and the furnace was getting power. I checked from "C" to "R" and from "C" to several other points. Here's a picture of my terminals: [img]https://cimg0.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/img_20220412_080759805_20214f95c170c833a69075ea9ab93d39fedcaed4.jpg[/img] 3. Next thing I checked was that the transformer was getting 120v in and putting out around 24v. I got 120v AC coming in and 21 to 28v AC coming out of the transformer. 4. I replaced the 5amp fuse on the board - the old one looked fine and I verified that it was with a continuity check, but I replaced with a brand new one anyway. Nothing is obviously burnt / malformed on the board itself. I'm guessing I'm looking at a board replacement? Is my line of thinking correct here. My only other thought was the large capacitor next to the board - I'm not sure what that does or if it would have any impact on my symptoms. Thanks for the help. Here are a few extra pics for reference: [img]https://cimg8.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/img_20220412_080739404_49e871cfbc29ce719289da94486ba5b4414d9c15.jpg[/img] [img]https://cimg2.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/img_20220412_080731985_8d28a3abbc96dba198eecf185d3a63592d087594.jpg[/img] [img]https://cimg0.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/img_20220412_082719691_11dba4f807d8763580ea88a6a9b24112c60e5733.jpg[/img] [img]https://cimg1.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/img_20220412_080803907_hdr_2a3f64b753fad5f7bd7003d495d66c1e78152e68.jpg[/img]