A leaking water heater flex line can stop a simple job fast.
This is even more frustrating when the old lines worked for years.
In this case, the leak is at the water heater nipple heat trap.
Both the hot and cold flex lines are leaking there.
The other ends seal fine on the 3/4-inch MIP connections.
That tells us something important.
The issue is likely not the pipe thread side.
It is likely the gasket seal at the water heater nipple.
Many water heater flex connectors use a rubber washer or gasket.
That gasket makes the seal, not pipe dope or tape.
If the gasket shape does not sit flat, water can pass by it.
A thicker tapered gasket may not seal well on every nipple.
Some heat trap nipples also have a narrow or uneven sealing face.
That can make some flex lines harder to seal.
Over-tightening is risky.
It can crush the gasket and make the leak worse.
It can also damage the connector nut.
Always follow the connector maker’s instructions.
You can also review general water heater safety from the U.S. Department of Energy.
Question
Would 100% silicone grease help the Eastman gasket seal?
Answer
No, silicone grease is not the best fix for this leak. It may help a gasket slide, but it will not fix a poor fit. If the gasket is too thick, tapered, or not seating flat, replace the connector or use a gasket that matches the sealing face. Do not tighten past the listed limit.
What I Would Check First
First, shut off the water.
Then remove the leaking flex line.
Look closely at the rubber gasket.
Check for cuts, folds, or off-center marks.
Also, inspect the heat trap nipple face.
It should be clean, smooth, and free of burrs.
Do not add Teflon tape to the gasket seal area.
The gasket needs a flat surface to seal.
Tape on the threads will not stop this kind of leak.
If the Watts gasket worked before, the sealing face may prefer a flat washer.
That makes a new flat-gasket connector a smart choice.
You can learn more about water heater parts from The Home Depot water heater guide.
Best Fast Fix
The fastest safe fix is to try another flex connector brand.
Choose one with a flat gasket design.
Match it to the water heater nipple size.
The hand tightens the nut first.
Then use a wrench only as directed.
Turn the water on slowly.
Dry the connection with a towel.
Watch it closely for several minutes.
If it still leaks, stop and replace the connector.
If the nipple face is damaged, replace the nipple.
If you are unsure, call a licensed plumber.
A small leak near a water heater can cause major damage.
It is better to fix the seal now than fight water damage later.
I’m Chris Mayer, writing for Plumbing 101.
