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My water heater has a pressure relief valve attached to the top, with a downspout that drains on to the floor. There is a second release valve on the hot water distribution pipes, this one drains to the ground outside. what is the purpose of this second valve? Is it a code requirement?

My intuition is that is is designed to trip before the heaters release valve so water is blown off outside instead of on the basement floor. The distribution release valve is set to 125 psi, but I can't find a set point labeled on the heaters valve.

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  • What is your location in the world? Is this a dual system used for heating environmental spaces also?
    – Ed Beal
    Feb 7, 2021 at 23:55
  • Seattle WA. Hot water isn't used to heat rooms or floors Feb 8, 2021 at 1:52

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I have not heard of a TPR valve being required outside or further away from the water heater there would be less of a chance of valve opening for temperature the further away it was from the heater. I have seen reliefs on hydronic systems at a lower pressure to protect the embedded plumbing but not water heaters. Possibly a work around for a drain that the one at the water heater did not have.

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  • I'd expect one not on the heater to be pure pressure relief, rather than TPR.
    – Ecnerwal
    Dec 5, 2021 at 17:11

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