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I recently had a plumbing company install a tankless water heater in my crawlspace. Everything with the install works and looks great, but we are experiencing a very strong chemical smell (like nail-polish remover or a strong sharpie marker) that comes out of our faucets when we call for hot water. It usually lasts for about 10 seconds then goes away. I notice it whenever we haven't used the hot water for awhile. For example: the smell is very strong first thing in the morning when turning on the shower.

The plumbers used PEX pipes to install a hot water recirculation pipe that is soldered to the original copper pipes. Other PEX pipes were soldered where they needed to connect to some other areas of the copper pipes including a new Pressure Reducing Valve.

Does anyone have any insight or advice on what could be causing this issue?

Thanks, Mike

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    I suppose this could be from the flux used in soldering. – Jim Stewart Apr 12 '18 at 19:49
  • That is what I originally thought too. it's been a week now, and any water soluble flux should have been washed away and gone by now, right? – Mike Apr 12 '18 at 19:51
  • One would think so. – Jim Stewart Apr 12 '18 at 21:51
  • PEX soldered to copper? Don't you mean crimped to copper that was soldered to other solder? PEX doesn't leech, so I doubt it's the pex, did they use PVC on the supply side somewhere? – virtualxtc Apr 12 '18 at 23:01
  • It sounds like the smell you're describing is acetone (often in nail polish remover and sharpies as a solvent). I have no idea why that would be present though. – Hari Ganti Apr 12 '18 at 23:30
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I think it is burn-in of the heater from something inside the heat-exchanger since the wet side is a closed system. Believe I'm perplexed by the same problem, so let me expand to establish that we have the same complaint and I believe the same root cause. If those assumptions hold, our system similarities are of more interest and the differences are candidates to be dismissed. I put in a new propane-fired tankless water heater with integral recirculation pump and remote cross-over valve 4 weeks ago on CPVC piping in the garage. After the heater has been idle for a while, the water that has been sitting in it gets a strong chemical smell. You can't smell it at the heater, and it takes a while to pass through the pipes to the fixture (sink/shower) depending on the length of the pipe run. The smell only comes from hot water, so it is not coming from my well water (are you on well or public?). The smell goes away in a few seconds.

To me, there are still logic problems with this answer. If true, it would seem the complaint would be far more widespread and discussed online. Also, I hope to distinguish between water that's been sitting in the heat exchangers leeching the smell from sitting versus some smell coming from initial heating. I plan to do a test allowing water to sit overnight then disable the heater and run the hot water and see if it still stinks.

Note that the burner cannot in my opinion contaminate the water and the smell is IN THE WATER. Pipe dope from supply piping could contaminate the heat exchanger, but I found no residue on the inlet screen whatsoever.

Also note, we are NOT talking about iron or manganese induced rotten egg-smell

  • Hello, and welcome to Home Improvement. This is interesting, but doesn't answer the original question. – Daniel Griscom Oct 4 at 0:05
  • I could have worded it better, but I explicitly said "My answer" followed by my answer to the original question--think it is burn-in of the heater. – Geoff Oct 4 at 1:24
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    Well, would you mind wording it better? – Daniel Griscom Oct 4 at 1:45
  • PTFE is good to +/- ~500 degrees. A cracked heat exchanger, or a (plastic?) holding tank operating above its recommended temperature is all I can think of. Call the manufacturer. – Mazura Nov 3 at 19:56

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