Hot water heater had a constant slow drip from the discharge pipe which was connected to the t&p valve AND the thermal expansion relief valve/shutoff valve. No expansion tank in the system. I removed the t&p valve and it was covered in corrosion/rust. ‘Plumber Friend’ told me to replace the water heater if that much corrosion was present. So I did Thinking the t&p was the cause of the drip. New water heater installed (By me) and still have a drip. So I replaced the old Apollo thermal expansion relief valve and it still drips constantly...and it now whines constantly! Both Old and new thermal expansion relief valves are 80 psi. House water pressure is 70psi. What am I doing wrong? I understand thermal expansion and that the relief valve will drip when water is being heated but should it drip constantly? The most common thermal expansion relief valves are set at 125psi. The guy I ordered the new one from said “are you sure you want the 80 psi? I’ve never sold one of those. We mostly sell 125 psi.” But since the original was 80 psi I stuck with it. Can I upgrade to the the higher psi? Would it damage my pipes?

not the pipe, but, your FIXTURES will experience SEVERE 'wear and tear'

sounds like the relief is actually working properly and doing the job

you actually need a compression, commonly miscalled an expansion, tank to 'absorb' the expansion created by the water heater


70 psi is borderline high, but, if supplied by the main in the street, is A-OK

if you have a PRV on the incoming main set it DOWN to 50 psi





expansion tanks are actually open to atmosphere and used in gravity flow heating systems

compression tanks are used in closed pressurized systems


a nit well picked by an 'old school' pipefitter

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638



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Put an expansion in! You probably have a closed system and every time the heater kicks on, you will get drips if there is no where for the expanded water to go.