Came out today for a Lennox furnace not operating. Upon inspection I found that the 2 furnaces were twinning furnaces. System #2 was trying to operate but there was an issue with system #1. System #1 has an error code open rollout switch. I took my volt meter and checked each switch. I received a reading of 27 volts at each switch going in and coming out. I proceeded to jump out each switch one by one and try to start the system. I had no success. I jumped them out at the same time and fired up the system. The control board is still giving an error code for a rollout switch. This is an indication that the system has a bad control board. The system is currently 21 years old and tracking down a new board may be an issue. I was able to bypass the second system so the homeowner would have heat. Chud will have to reach out to the homeowner with a proper repair quote. Lennox furnace model #g50uh-36b-090-02, serial #5801j52882. See photos