water pressure reducing valve failure modes?

My water pressure reducing valve will control pressure under flow and can be adjusted to various settings. But when flow is shut off, pressure jumps to about 125 lbs/sq inch almost instantly regardless of pressure when there is flow. Thus this is not a water heater thermal expansion issue.
Does this mean that the pressure reducing valve needs to be replaced? Present unit is about 15 years old, Watts 25 AUB.
Thanks.
John
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John Shaeffer wrote:

Yes, it is not seating and sealing perfectly, thus allowing some small flow regardless of downstream pressure. You might be able to repair it, but i think you're better off getting an identical unit and swap it in.
Jim
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