stumblin, bumblin benchmark boiler

[MUNC]

Hey guys need a little in put about a Benchmark 2.0 boiler. 16955 hours on it. 6-7 years old. I think never setup from install. NOTE three others tuned ok but this one gives me fits. At 40% fire rate flue gases spot on @ 16% fire same,spot on. Then when you take it to 100% you can't get past 80% fire rate and the thing starts to sputter and pop out the flue. My co goes above 10,00ppm. O2 drops to near zero, cant get gas pressure to the spec of 7.0"wc. all other boilers on same gas line all no problem. Removed combustion air hose to see if something was resticting air= same. pulled burner and saw that some of the "swirl turbulator" fins where bent over from getting too hot. reassembled after cleaning burner and same thing. is there a spec for an air side pressure drop across these exchangers? and is there a good place to take readings on the air side? All 4 boilers got the seasonal kits so flame rods and igniters new. Could low gas be caused by the combustion back firing which is a product of a partialy plugged x-changer? ( O.K.@ 16 & 40%) Any way of visiualy inspecting lower portion of air side of x-changer short of pulling the whole thing out and and tearing it down? If this thing was a car i'd say the timing chain has jumped it pops that bad. Any ideas will be greatly appreciated thanks MUNC

[gem6376]

What type of Burner? Does it have a jack shaft? You need to make sure that there is not a sooting problem. And then make some a adjustments. I would recommend 30 exess air all the way thru the firing rate.

[pringlel]

If your at 100 firing rate and your 02 is 0 then your problem isnt to much fuel. are you checking gas pressure at inlet to gas regulator or manifold pressure. Manifold pressure usually is allot lower, If no manifold gas pressure specs you may want to make adjustments to obtain 4 % 02 and o co or as close to 4% 02 with a 0 Co.
I have never worked on a Benchmark, Sounds like its a full modulating burner.
I would call them and request a burner setup spec sheet. Chamber pressure, manifold pressure, inlet pressure , min - max burner firing rates temp rise etc.
If its the heat exchanger clogged , should get higher than normal flue temps even at 40% and you should see an excessively high chamber pressure as it loads up.
IF ya can clean the x changer i always do it before tuning the burner, much more accurate and better readings.