Spot the Violation

PlumbingWater heatersLevel 32018 UPC

Water service and heater in the mechanical room

Basement mechanical room with a poured concrete wall. At the left, a 1 in. copper water service rises through the slab to a ball valve, turns horizontal through a bronze water meter with a bonding jumper clamped across it, a second ball valve, a bronze bell-housed pressure-reducing valve with an adjusting screw on top, and a tee with a pressure gauge, then climbs to the ceiling. The cold main runs along the joists to the right and drops through a ball valve into a gas water heater, whose hot line rises back into the joists. The heater has a draft hood and vent, a gas line with a shutoff and drip leg, and a relief valve with a copper discharge pipe ending near the slab by a floor drain.
Basement mechanical room, water service entrance and water heater

What's wrong here?

  1. The pressure-reducing valve makes this a closed system, and there is no expansion tank or other thermal expansion control
  2. A pressure-reducing valve may only be installed where street pressure exceeds 80 psi
  3. The water meter must have a bonding jumper around it
  4. The pressure-reducing valve must be on the hot water outlet of the heater
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Show the answer and the code reference

The answer

There's a PRV on the service but no expansion tank. With the heater on a closed system, nothing takes up the thermal expansion of the heated water.

Correct choice: 1. The pressure-reducing valve makes this a closed system, and there is no expansion tank or other thermal expansion control

A pressure-reducing valve lets water into the building but won't let it push back out to the main. Every time the 40 gallons in the tank heat up, the water expands and has nowhere to go, so system pressure spikes until the T&P relief valve weeps or opens. That wears out the relief valve, faucet cartridges and toilet fill valves, and strains the tank. UPC 608.3 requires an expansion tank or other approved device on any system with a check valve, backflow preventer or other normally closed device that keeps building pressure from bleeding back to the main, and a PRV is such a device. Where the PRV is there because street pressure exceeds 80 psi, 608.2 says it directly: an expansion tank goes in the cold water piping downstream of each regulator.

How to fix it

Install a listed potable-water thermal expansion tank (NSF 61), sized for the heater volume and street pressure, on the cold water line downstream of the PRV, usually on a tee in the cold line above the heater. Pre-charge it to the PRV setting before filling the system and support it per the manufacturer's instructions.

Code references

  • UPC 2018 608.3 — Expansion Tanks, and Combination Temperature and Pressure-Relief Valves

    A water system with a check valve, backflow preventer or other normally closed device that prevents building pressure from dissipating back into the water main shall have an approved, listed, adequately sized expansion tank or other approved device to control thermal expansion, whatever type of water heater is used, installed on the building side of that device.

    Drills citing 608.3

  • UPC 2018 608.2 — Excessive Water Pressure

    Where static pressure exceeds 80 psi, an approved pressure regulator preceded by a strainer must reduce it to 80 psi or less. An approved expansion tank, suitable for potable water and installed per the manufacturer's instructions and listing, shall be installed in the cold water distribution piping downstream of each such regulator to control thermal expansion and hold the regulator's setting.

    Drills citing 608.2

Minnesota

MN status unverifiedConfidence: medium

Minnesota adopts the 2018 Uniform Plumbing Code with Minnesota amendments as the Minnesota Plumbing Code (Minn. Rules ch. 4714, effective Dec. 17, 2021). Search results indicate Minn. Rules 4714.0608 amends parts of section 608 (the relief valve discharge rules in 608.5, at least). No Minnesota change to the expansion tank requirements of 608.2 or 608.3 is known, but that has not been confirmed against ch. 4714.

About the Minnesota Plumbing Code

Citation under review. Confirm that Minn. Rules 4714.0608 leaves UPC 2018 608.3 (expansion tank where a check valve, backflow preventer or other normally closed device makes the system closed) and the expansion tank sentence of 608.2 unamended. 608.3 is now the primary reference because the scene does not show street pressure, and the 608.2 sentence applies to 'each such regulator', that is, regulators installed because static pressure exceeds 80 psi.

Why the other choices are wrong

  • A pressure-reducing valve may only be installed where street pressure exceeds 80 psi. UPC 608.2 requires a regulator when static pressure exceeds 80 psi; it does not forbid one at lower pressures. Lots of Minnesota homes have one at 60 to 70 psi street pressure.
  • The water meter must have a bonding jumper around it. It already has one. The copper jumper clamped on the pipe each side of the meter keeps the metal piping bonded when the meter is pulled.
  • The pressure-reducing valve must be on the hot water outlet of the heater. A PRV belongs on the cold service ahead of the distribution system so the whole building is regulated. It goes downstream of the meter and main shutoff, which is where this one is.
Code complianceLevel 3 · Master#expansion tank#thermal expansion#PRV#pressure regulator#closed system#water meter

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