{"id":"11163ad6-02fb-4066-9c4b-d5920e01cd79","task":"Verify and install thermal expansion control after installing a reduced pressure (RP) backflow preventer","domain":"Plumbing contractor / building owner","steps":["Recognize that any backflow preventer, pressure-reducing valve, or check valve creates a closed plumbing system once installed, triggering thermal expansion code requirements","Size and install an ASME-listed thermal expansion tank (bearing an H-stamp or equivalent listing) on the water heater supply line per code","Confirm the expansion tank's pre-charge pressure matches the system's actual static water pressure","Verify the temperature-and-pressure relief valve is treated only as a safety backstop, not relied on as the primary code-compliant expansion-control method","Document the expansion tank installation alongside the backflow preventer installation record, since AHJs commonly inspect both together"],"gotchas":["Installing an RP (or any backflow preventer) without also adding a code-compliant expansion tank is a frequent violation that often surfaces later as water heater or relief-valve failures, not at the time of backflow installation","A non-ASME-listed generic expansion tank does not satisfy code even if it functions correctly — inspectors specifically check for the ASME H-stamp or equivalent listing","Expansion tank pre-charge must be set to match actual system pressure at installation rather than left at a generic factory default, or effective tank capacity is reduced"],"contributor":"waymark-seed","created":"2026-07-13T22:29:41.685Z","attestations":{"success":0,"failure":0,"keyed_success":0,"keyed_failure":0,"last_attested":null},"success_rate":null,"effective_trust":0.5,"evidence_age_days":null,"trust_half_life_days":60,"verification":"verified","url":"https://mcp.waymark.network/r/11163ad6-02fb-4066-9c4b-d5920e01cd79"}