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Electrode Assembly: Question on flame sensor and when to replace

jdbs3
jdbs3 Member Posts: 34
in Gas Heating

Bosch Greenstar Residential Gas Condensing Boiler, Model ZBR 21-3. Installed Dec-2019.

Preventative maintenance is done yearly, and the gas boiler has been / is running well.

See picture of electrode assembly. The single electrode on the left is the flame sensor, aka ionization rod. From a google search, signs of failure are:

• Cracked porcelain casing: There is no sign of this.
• Presence of soot or debris on sensor:  It might be soot on sensor (see picture), but this can be cleaned with steel wool.
• Sensor tip is blackened:  There is no sign of this.
• Corrosion on the tip:  There might be some. The flame sensor rod on a new electrode assembly looks slightly thicker than the tip in the picture.  So it looks like flame sensor rods can deteriorate over time?  Correct?

A flame sensor lifespan expectancy can be from 5 – 20 years. This one is just short of 5 years.

Does this look like a flame sensor that needs to be replaced?

Thank you!

Electrode Assembly.JPG

Comments

  • HVACNUT
    HVACNUT Member Posts: 6,101

    Do you have the combustion numbers from the last maintenance? If that's the same assembly as the GB-142 (looks like it), and it looked like that at the time of the maintenance, then something doesn't make sense.

  • Big Ed_4
    Big Ed_4 Member Posts: 2,947

    I would recommend replacing once every 5 years , the flame sensor is not a issue .. The electrodes seems to walk in 5 ….

    There was an error rendering this rich post.

  • SuperTech
    SuperTech Member Posts: 2,291

    Yeah that absolutely needs replacement. Look at that versus what a new one looks like and it's obvious.

    The biggest thing is why does it look so bad? Is the fuel natural gas or propane? Has anyone ever done a combustion analysis with a digital combustion analyzer? If yes, what were the results? How is the boiler vented? Is the combustion air intake pipe possibly recirculating the boiler exhaust?

  • jdbs3
    jdbs3 Member Posts: 34

    SuperTech, all,

    RE Fuel type - Natural gas

    RE: Has anyone ever done a combustion analysis with a digital combustion analyzer? Not sure.

    RE: How is the boiler vented? See picture - through the back roof of house.

    *** Bosch Residential Gas Condensing Boiler ZBR 21-3.jpg

    RE: Is the combustion air intake pipe possibly recirculating the boiler exhaust? Don't know.

    RE: Yeah that absolutely needs replacement. Because of the flame sensor and/or the 2 electrodes?

    The electrode assembly is the original one that came with ther boiler, so the flame sensor is just about 5 years old. Combustion test results for 2022 - 2024 are attached.

    HVAC NUT,

    RE: If that's the same assembly as the GB-142 (looks like it), and it looked like that at the time of the maintenance, then something doesn't make sense. What does not make sense? Your thoughts after seeing the combustion test data??

    Thanks to all!

    Combustion Test Results - 2022.JPG
    Combustion Test Results - 2023.JPG
    Combustion Test Results - 2024.JPG

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