2400 exhaust fumes when first starting

[dougdnh]

My 2400 is giving off exhaust fumes when the burner first comes on. It seems to go away after a about a minute or so. I had the whole unit rebuilt 5 months ago, and the heat exchanger was replaced. The repair person came back a few weeks later and replaced the exhaust O ring. However, the smell is still there. I took the front grille off and slightly tightened the screws on the burner window to see if that would help, but no luck. Is there anything else I can check out?

[wjcroft]

Hi Doug,

I have a hunch that other Monitor experts here would have further tips. Such as Tom hawkins111 . I have the smaller older Monitor 422, and it also has a brief exhaust smell only at cold startup, it disappears quickly and is gone in less than 15 seconds.

I used a 'sniffer' like this to probe around at the various gaskets. Amazon has a range of similar units:

https://www.amazon.com/gp/product/B07GVN4DPR/

"Gas Detector Portable Natural Gas Tester Detector | Combustible Propane Methane Gas Sensor Sniffer with Sound Light Warning"

My strong impression is that my leakage is with the worn / original gasket between the combustion chamber and the heat exchanger. The detector seems to confirm this. Note that these detectors are intended to detect 'combustable' gas, but they also trigger on the heat of exhaust gas. You adjust the sensitivity of the detector with a knob, so it triggers on the differential between 'normal', and 'hot gas' (or natural gas / propane).

I did a complete burn pot / ring refurbish in fall 2017. So that included all new gaskets EXCEPT the heat exchanger one, because I assumed it was doing ok (including new o-rings on exhaust pipes). Overlooking the heat exchanger gasket was a bad assumption.

Other than this annoyance, the 422 is working fine. I'm just living with the brief whiffs of exhaust for the moment, as replacing this exchanger gasket would require all new gaskets and a sizable chore.

Best regards, William Croft, Mount Shasta, CA, USA

[hawkins111]

I would look closely at the exhaust connection to the heat exchanger. Both ends need to go all the way in. This is hard to do sometimes if the stove doesn't line up just right. Use a little anti seize on the "o"ring on both sides of the connecting pipe.

[ctbale]

My guess is its in the exchanger or top of the burner. I never disassemble the exchangers when I do overhauls. I normally just shake them and see how much carbon I can get to come out. But there are several gaskets in that heat exchanger that could be causing your problem. Maybe the window gaskets. Not likely it's the flame rod gasket. And not likely it's the igniter gasket. You said the exchanger was replaced but I'm guessing it wasn't brand new. I'd be taking that thing apart