How can I fix this persistently leaky shower faucet?

Question

Several weeks ago water began slowly dripping from the shower head in our master bath. Also, the underside of the hot water faucet is wet long after the water has been turned off and the shower has dried (except a small area kept wet by the drip), so I assume it's the problem. I have tried

1. replacing the seats and springs (which seems to have slightly increased the leak)
2. putting a thin layer of vaseline around the seat and on the back of the stem unit assembly (no impact)
3. replacing the stem unit assembly (negligible improvement)

Here's a portion of the parts diagram for a similar faucet (from Delta's website) for reference.

I don't know what else to try. What else could be the problem?

Answer 1

You say you replaced the seats. The seat is where the usually rubber washer on the end of the stem seals against the back of the valve body. If you put your finger in the hole where the stem goes you should be able to feel the surface where sealing takes place. This surface can get scratched and allow leaks. In fact, the leak can make the scratch worse over time. Also, debris can become trapped in this space during repair and prevent sealing. So, make sure the seat is not scratched, it can usually be replaced if it is, and make sure no debris is left behind before closing up. Additionally, there is usually a washer made of paper fiber or hard plastic that sits between the valve body and the stem above the threads. If this washer is worn or missing leaking can occur at that point.

Finally, you say you replaced the seats and it got worse. It is possible the seats are not tight or are installed incorrectly, crooked, or cross threaded preventing the washer from seating. Check for that.

Good luck!

Answer 2

The problem may be elsewhere. Being that you say it is the Hot water that is the problem, have you looked at your hot water tank recently?

• Is there water by the over-pressure vent pipe?
• Do you have an expansion tank that may be bad? Tap on the tank with a screwdriver. Does it sound hollow? If so this is normal indicating that air is inside the tank. If it sounds solid, than the internal bladder has probably ruptured and the tank is filled with water. This means there is no where for the hot water to expand to and therefore the pressure in the hot water lines has increased. Your shower hot water faucet could be the weakest link, showing a problem there first.

EDIT: Pressure relief tanks get connected in the cold water pipe, by the water heater. When the hot water heater runs, the hot water expands increasing pressure. Before expansion tanks, this pressure was allowed to build up in the water main, and back to the utilities main. This started to become a problem for utilities with the added pressure from all neighborhood's houses. So someone came up with the idea to add expansion tanks within the home. These tanks absorb the increased pressures, so that the fixtures within the home only see a steady regulated pressure, and the main stays constant pressure.

Try running cold water in a nearby sink while looking at the troubled hot water faucet. If if stops leaking with the sink running, that should give an indication of it being a pressure problem. In any case, I would start with measuring the water pressure so you can determine if it's a pressure problem or just a faucet fix.

Could be you need an expansion tank. Can you measure the water pressure? Big box stores sell cheap pressure gauges for ~ $10 - look for it in by the irrigation plumbing. You can hook it to your outdoor hose bib, Wait for the water tank to kick in and heat the water (or when the faucet shows a leak) then see if the cold water pipe PSI increases.

By me, all new housing has to have an expansion tank.