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Viessmann wall hung condensing boiler giving repeated F1 errors. Flue gas temp high.

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hottubbrad1
hottubbrad1 Posts: 1
in THE MAIN WALL

Model B1HA 94. SN: 7560853804181118

B1HA 94, hydronic-only, on LP, with a 50/50 Chemfrost glycol/water hydronic system on a primary/secondary loop. No makeup water as it is using an injection tank. It ran trouble-free for about six years and is now locking out on F1 repeatedly, even at minimum modulation. Work done so far: water-side descale with citric acid, full combustion-side clean. The circulator is confirmed running and system pressure is normal. After the work, with the setpoint at 124°F (51°C), supply ran 124–131°F (51–55°C). Flue gas started at 195°F (91°C) and climbed to about 221°F (105°C) at min fire. That’s roughly a 90°F (50°C) delta between flue gas and supply. I haven’t put an analyzer on it yet; that’s next. With water-side scale, fireside fouling and the flue gas sensor tested, I’m looking for input on what’s left.
Questions:
1 Could sludge buildup in the HX be restricting flow or heat transfer enough to cause this?
2 On a 6-year-old glycol fill with Oxybarrier PEX is there any Viessmann related advice here?
3 Any known failure points around the 6–7 year mark that would drive up flue temps?

Comments

  • jesmed1
    jesmed1 Posts: 1,613

    Not an expert, but have you checked the flue pipe for blockage? What about condensate drain?

  • GGross
    GGross Posts: 2,066
    edited 6:30PM

    Open burner, look in back where the refractory is located. there is a hinged ring back there that holds the plate in place, which in turn holds the refractory in place. if that piece looks warped, bent, or in any damaged in a way that would allow the burner flame to get past the refractory document it with photos and contact tech support with model serial and info. they are processing heat exchanger warranties for this when i come across it. in the past we used to just replace that baffle piece.

  • GGross
    GGross Posts: 2,066

    I am fairly confident its the baffle issue but just to clarify some of your questions

    1. not really, theoretically yes I suppose but if flow were restricted beyond acceptable levels the internal flow switch would shut the boiler down. its possible to have scale preventing heat transfer but still not at the level you are seeing without also restricting flow imo
    2. standard glycol service, check for concentration and if you need inhibitor etc
    3. just the flue baffle! seems pretty random, we had a run of them that did it a few years ago and then it mostly went quiet. had a couple more this past year though and now tech support is warrantying the whole heat exchanger.

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