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Contant Drip from T&P

I have a reoccurring problem with a T & P valve on a Buderus 79 gallon sidearm with heat supplied by a GB-142 boiler. The T & P has a continual drip that seems to occur during the heating of the water. The house has a booster pump where the ¾” water enters the house; I added a domestic expansion tank and spring check valve on the cold water line entering the sidearm. This did not correct the problem so I added another expansion tank on the hot water side of the sidearm, however, the problem continues. I appreciate any suggestions offered to help remedy this problem.


  • Larry C_8
    Larry C_8 Member Posts: 7
    What is the setpoint of the T & P valve.

    What is the shut off pressure of the booster pump?

    80 gallon water heater and how much temperature change from cold to hot?

    How much expansion volume?

    What is the setpoint of the T & P valve.

    Do you experience water hammer when the toilet, dishwasher, clothes washer, water softener, refrigerator, shower, or any other water using appliance shuts off?

    Max pump pressure + thermal expansion + possible undersized expansion volume + water hammer = dripping valve ?

    The spring check valve on the cold water inlet to the water heater just removes the cold water piping as part of your expansion volume. If the domestic expansion tank is upstream of the check valve, it is effectively isolated from the hot water system and does nothing to absorb the heating induced expansion.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    position of the check

    Where did you put the check valve in relationship to the expansion tank? I've a seen a plumber install the check between the indirect and the expansion tank. This will not work. The check should be between the expansion tank and the cold water feed source. The expansion tank should be on the cold water side.
  • JOHN_103
    JOHN_103 Member Posts: 54
    t&p leaking

    did you check the pressure on your extrol before you installed it? if not you need to check the tank and match it to your cold water pressure
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