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Rising pH level in boiler system

BoilerToolbox Member Posts: 12
Hello, what would cause the pH level in a closed loop boiler system to rise from 7.9 to 8.9 over the course of a year? The city fill valve is closed off so it is not an issue of the pH being too high in the fill water. Even at that, the city water sample tested at 7.9 pH. 

The boiler is a P-K Mach C-450, 2007 vintage installed in a church. It is all copper pipe serving fin tube baseboard. 

They have tested the pH annually over the life of the boiler and never had it higher than 7.9, they have never treated the boiler water either.



  • hot_rod
    hot_rod Member Posts: 22,505
    Shat is the water tested with?  The electronic meters should be calibrated yearly. At least test accuracy with the test fluid packets

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • BoilerToolbox
    BoilerToolbox Member Posts: 12
    It was tested with a calibrated meter this time. Previously I’m not sure how it was tested. 
  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    edited April 2023
    What kind of meter do you have? Unless you use it on a regular basis, it should be calibrated before you use it. If you have a scale, 230 ml of water is equal to 230 grams of water.Give the meter time to acclimate to the water temp.

  • Derheatmeister
    Derheatmeister Member Posts: 1,572
    As others have mentioned make sure that your PH measuring equipments probe is stored in the storage fluid..Give the probe some time to react, and make sure that the PH meter is calibrated.
    If you are uncertain about your measuring equipment you can send a sample to a professional company such as Rhomar to have it analyzed
    If the PH is high in your Closed loop heating systems keep in mind that there is a thing that is called self alkalization Process which MAY be what the system is experiencing.
    In the PK manual section 3.7.4 the instructions on behalf of the system fluid are not straight forward.
    Here is some infomation from the VDI 2035:
    C. Aluminum and aluminum alloys
    Corrosion to aluminum is primarily determined by the pH value of the heating water. In the
    presence of water within the pH range of 6.5-8.5 aluminum is able to form a protective layer of
    aluminum oxide, which protects the underlying metal against further corrosion. This layer is
    broken up, however, in acidic water with a pH below 6.5 or in alkaline water with a pH above 8.5.
    At these pH levels (<6.5 or >8.5), corrosion damage is likely to occur even in oxygen-free water.
    Systems containing aluminum are best operated at a low saline level (electrical conductivity
    <100µS/cm) and without the use of chemical inhibitors or electrochemical devices. If aluminum is
    used in conjunction with other metals, such as steel and copper, the recommended pH of system
    water is 8.2-8.5. Since maintaining this pH range will likely be unfeasible, low electrical
    conductivity is recommended to limit corrosion damage.
    Flow velocities >2m/s may also cause erosion to aluminum

    I would get in touch with the Manufacturer and obtain better data on the expectation of the system fluid.