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I have a low micro-amp signal (.3) which is causing this 10 year old rheem 80% furnace to lockout. I cleaned and then replaced the sensor but still the same reading. I thought it might be a grounding problem so since the panel was so close I ran a new wire diectly to the panel and still same problem. This is a weird one. All the years in the business I still don't understand 100% how the sensor works. I didn't check the AC voltage to the sensor, I know the board is suppose to do this, and I remembered that on my way back to the shop. What should the voltage be? I suspecting the board may be the problem, but before I do that i'm going to get a clamp to run a ground wire to the cold water line, and maybe bypass the sensor and ground wires around the molex plug that goes from the burner cabinet to the blower compartment. Any other ideas, I haven't had a good one like this in quite awhile. Thank you