Rannai pressure release valve leaking

[shawndh]

I've been hearing a hissing noise in my pipes for weeks now and I finally realized it was coming from the tankless water heater. I was out on the porch and I saw water dripping from the unit. When I opened it I heard the hissing noise and saw that the water was coming from the PRV. I pulled on it and let some water through (cold water) and the hissing and leaking stopped.
A couple weeks ago prior to this, I adjusted the pressure valve for the water coming into the house to reduce the water pressure. I was thinking that the pressure was too high because of the hissing and banging pipes. I noticed that the pressure is less coming from the faucets but I still got the hissing and the knocking has been significantly reduced.
Is there a problem with the tankless water heater or am I having water pressure problems? I'm confused because the pressure is just bearly strong enough for a good shower.

[Dana]

PRV valves fail often- could be yours has too. But first things first:

Have you MEASURED the water pressure in the house? If it's too low it could be an issue with a tankless too, showing up as some sizzle & bang on the water side of the heat exchanger, as larger bubbles form & collapse on the hot walls of the tubing. This is more noisy than dangerous, but cuts into efficiency since the bubbles insulate, reducing the effectiveness of the heat exchange. IIRC some manufacturers spec 15psi, as a minimum operating pressure, but 25-35psi would be better if you can, since at higher flow rates there's a significant pressure drop across the tankless.

[Scott D. Plumber]

I agree with Dana. Check your pressure first, If in the normal range of 40-60PSI get a new PRV.

[shawndh]

Thanx for the info. I still haven't measured the pressure in the house yet, but I'm thinking it's the PRV as well. I'll post my findings.