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Modcon flue gas smells of gas

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rhl
rhl Member Posts: 100
Hi,

I've noticed a condition were on startup we smell gas from the boiler flue pipe just for a moment before we start seeing the white flue gas.

Modcon aqua balance combi boiler.

I replaced the flue gas sensor (which was corroded) and the ignitor -- went ahead and vacuumed out heat exchanger and cleaned per manual.

Refractory is partially worn -- will replace when new part arrives.

Boiler was installed in 2018.

Is this normal? Anything else to check?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,450
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    Are you smelling gas -- or combustion products? Both have an odour, but are quite different.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mattmia2
    mattmia2 Member Posts: 9,750
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    did you do a combustion analysis on this? Might not be unusual for a small amount of unburned gas to be emitted as it is lighting
    Zman
  • HVACNUT
    HVACNUT Member Posts: 5,865
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    Are you smelling this outside at the exhaust or inside at the boiler?
    You might get a good whiff if you're near the exhaust outside on ignition only. Inside, that needs to be checked. Do you have a combustion analyzer and manometer?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,631
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    Do a combustion analysis. If it lights ok and the combustion test is ok I wouldn't worry about it
  • rhl
    rhl Member Posts: 100
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    Outside the boiler -- I don't have one personally -- will ask plumber. thank you everyone.
  • HVACNUT
    HVACNUT Member Posts: 5,865
    edited November 2021
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    rhl said:
    Outside the boiler -- I don't have one personally -- will ask plumber. thank you everyone.
    You don't necessarily need a plumber. A service technician familiar with mod cons and the correct tools is who's needed. Come back and let us know. The tech should leave a printout or email you the combustion report. 
    mattmia2
  • Jamie Hall
    Jamie Hall Member Posts: 23,450
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    You don't necessarily even want a plumber. Not all of them have any idea how to adjust a mod/con...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    mattmia2