I have had a nice Bosch non-condensing tankless for about a year now. Just have not found the time to take on the install, but I am now ready. I need to install my exhaust vertically because of the install location. I am installing it next to a high efficiency furnace I put in about 2 years ago. The subsequent furnace was a 80% efficiency from the 50's. So the chimney it used was good for some pretty high temps. The chimney is not currently being used. I plan to run my exhaust up through that chimney. My question is do I HAVE to sleeve it/run exhaust pipe up through it for the following reasons. I am thinking if I have a condensate drain, before the exhaust goes into the chimney, then no corrosive elements would make it into the chimney. And since the chimney was designed,built and used for high temperature flue gases- the tankless exhaust temperatures will not be a problem. So assuming my chimney is still in good shape... Anyone with knowledge or experience that can help me with this? Thanks for your time.

I have a Weil-Mclain WM97+ 155 boiler/furnace. It gave me a lot of troubles recently. The main problem that I am facing is it gives me "Flame Fault" error from time to time. Based on the manual, that error means there are flames detected when it shouldn't, and the possible reason is the gas valve could not close properly. When I first saw this error, I checked for flames through the observation window, no flames spotted. Then, I reset the boiler and it ran with no problem. one or two hours later, I found that the error come up again. I checked again, no flame, then reset, hours later, same error. I sat next to the boiler for a while and watched it finishing a few full cycles (presurge, fire, postsurge...). Moments later, I witness the error happening. After the boiler finished the heating request, it closed the gas valve and entering the postsurge stage. But on the display, it shows it detected weak flame signal. I checked the burner, no flames in visual. I even disconnected the connecting wire between the flame igniter/sensor (they are the same thing for this boiler) and the display still shows some reading for flame. Then it lockout and shows error "Flame Fault". I reset it immediately, but it still shows readings jumping (4, 8, 16, 40, 4, etc.). I tired to see what's the current between the control board to the flame rod with a multimeter. The moment I connect the connecter to ground with my multimeter, the reading goes to 0. Right now, I have to keep resetting it since I don't know what's going on. Does anyone have any idea about what's going on here? Is that indicates I have a faulty control board? I checked online for the control board, it turns out Weil-Mclain does not want me to replace the board only, I have to purchase the entire control unit assembly (including display etc) at 800 bucks, so I really want to exhaust all other possibilities first.