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Expansion tank questions

Le John
Le John Member Posts: 226
Happy Holidays Heating Help.
On a properly functioning expansion tank should the system pressure increase as water is heating up? Cold the system pressure reads 13 and when two zones calls it increases to 15 but then when cools falls 13 again. Etc. The pressure in the tank reads about 12.


  • mattmia2
    mattmia2 Member Posts: 9,734
    Sounds like it is working properly. The expansion tank compresses air to compensate for the incomressability of the liquid. When you cram the same mass of air in to a smaller volume, the pressure increases.
    Le JohnSTEVEusaPAdelta T
  • HomerJSmith
    HomerJSmith Member Posts: 2,467
    Hot water expands as it is heated. Yes. The sys pressure should rise a few degrees when the boiler is at full temperature from a cold start.
    Le John