Looking for tips sealing water to/from a tankless water heater

[WV Bob]

My bro-in-law is fighting a losing battle trying to connect 3/4" PEX to his tankless water heater. The water connection on the heater is 3/4" FNPT. The PEX fittings (Sioux Chief brand) are marked 3/4 IPT on the package so I think he's using the right size. There is no apparent thread damage and it all threads together most of the way by hand with no binding or obvious problems.

He has replaced the fittings more than once, has tried both brass and plastic fittings, and every single time, water seeps at the threads. He has tried both white teflon tape and pipe dope, but not both at the same time. Nothing he has tried has worked.

The inlet/outlet on the heater is brass. It's basically a special purpose union with the T&P valve and other fittings cast into it.

I'm looking for any advice on what will fix this problem. Is it possible he over-tightened it and distorted the brass fitting? Is there anything else he should try? I will recommend trying both tape and dope, based on posts in the pinned Teflon tape thread here.

Any suggestions on what we should try next are appreciated.

Bob Inscoe
Huntington WV

 

[Reach4]

He has replaced the fittings more than once, has tried both brass and plastic fittings, and every single time, water seeps at the threads. He has tried both white teflon tape and pipe dope, but not both at the same time. Nothing he has tried has worked.

I would use both at the same time. I would upgrade from the cheapest PTFE. I think yellow tape suitable for gas or Oatey Pink tape is a worthwhile upgrade.

Use enough torque. Longer wrenches make that easier. A box end wrench is better, and 6-point is better than 12-point. Use two wrenches if there is a hex available on water heater.

 

[Sponsor]

 

[WV Bob]

I would use both at the same time. I would upgrade from the cheapest PTFE. I think yellow tape suitable for gas or Oatey Pink tape is a worthwhile upgrade.

Use enough torque. Longer wrenches make that easier. A box end wrench is better, and 6-point is better than 12-point. Use two wrenches if there is a hex available on water heater.

Thanks.

He's using what looks to be a 12" crescent wrench and a similar sized pipe wrench when tightening, pushing against each other. Sufficient torque isn't the problem. I will recommend the yellow tape since I have some here somewhere.