Hello DYIers!. Long time reader, first time poster here. Just wanted to share my experience and maybe get some feedback. I have 2004 Weil-McLain oil fired 125K BTU/h boiler providing hydronic heat and hot water (via heating coil) which I converted to NG by replacing burner head with Carlin. That had been set up with wide flame pattern based on firebox shape and Carlin recommendations. As the boiler is significantly oversized for the house it is also underfired at ~110K BTU/h (boiler expects to be fired at ~145K BTu/h). As I dont have combustion analyzer access, in the past I would set up the boiler by the trace of smoke (zero smoke actually) and that worked quite well with oil. For some reason I decided post conversion smoke pump will be unusable and promptly sold it. However now I have dilemma as I am not in position to buy and maintain combustion analyzer. I do have generic car O2 sensor (heated kind -4 wires) and decided to try using that. I plugged it into the chimney pipe on top, attached to 10A 12V power (old computer PSU) to two of thewireswith thesame color and let it warm up for 15 minutes. Once warmed up attached my digital multimeter to two other leads. That shows 10 mV or less. Now opening air slits to 50% and starting the boiler. Voltage up to 30 mV but we are on flat part of the curve with lot of excess air. Now slowly closing air slits on the burner and observing sensor voltage. At some point it jumps to ~900 mV indicating no free oxygen. Moving air slits one way and other found location where it jumps between 50mV and 900 mV. The curve is very steep so it will be hard to hit exact location to see output anywhere in the middle. But I can get the spot, on my burner it is at 35% open. To obtain best burning efficiency I must be at 10% excess air, perhaps bit more to be sure. That means widening the air slit by 10% or 3-4 marks so I now set it to ~40% open. O2 sensor reads ~50mV I verify it using following method: I have 4 air slits. I cover 1/3 of one slit (1/12=8%) and O2 sensor voltage is low - excess air. Then I cover 2/3 of one slit (16%) and O2 sensor voltage jumps to 900 mV - no free oxygen, insufficient air. Which means I am providing no less than 8% excess air but no more than 16%. Good enough for me. Am I missing anything?

Greetings. We have a Sears furnace manufactured by Inter-City Products - photos attached. Although 25 years old, much of the furnace has been recently upgraded - like within the past 5 or so years - new main blower, new heat exchanger, new 1F80-261 thermostat/control etc. Also new AC two years ago. Anyway I tried starting it up for the fall, I can hear it click but the gas and blowers don't click on. I went through the instructions on the inside panel, cut the electricity then turned off the gas valve shown in the photo - waited 5 minutes then turned it on, restored electricity and tried again to start. Still hear clicking in a relay - but no start up. Any ideas? I was wondering if the blower in the pic is dead? Or maybe the semiconductor on that blower? Any advice appreciated. [attach]109726[/attach] [attach]109727[/attach] [attach]109728[/attach]