Plumbing question

I installed a Bosch electric under-sink water heater in the bathroom of my shop & turned it on for the first time the other night...and it didn't go so well.

My understanding of this unit from the instructions includes the following 3-points that may or may not be correct: a.) it only heats the water while it's flowing & the heating element is off the rest of the time. b.) it's only capable of a max 40-degree temperature rise, so given that the cold water is about 45-50 degrees max, should put the hot water well under 100-degrees. And c.) CPVC 1/2" pipe is rated for hot water & has a melting point beyond 200-degrees.

Here's what happened:

After getting it all plumbed, wired & turned on, I turned on the hot water & was greeted with nice lukewarm water after a couple seconds. Satisfied, I turned off the faucet & left the room. About 2-minutes later I heard a loud "pop" & went in to discover that the transition from the 1/2"-copper NPT outlet to the 1/2"-CPVC line had melted & burst under pressure.

I'm planning on talking to Menards about it, but I'm sure there's far more knowledgeable people on here!

petegossett wrote: I'm planning on talking to Menards about it, but I'm sure there's far more knowledgeable people on here!

Tell the folks at Menards to focus on selling tires for ice racing.

what temp was the water coming out when it burst?

did it melt or did a glue joint fail? cpvc glue takes a long time to dry.

It actually melted the CPVC, which is what I found to be disturbing since supposedly it can only heat the water 40-degrees.

CPVC....why?

I've hooked up the 180degree hot water heaters before using braided steel lines for flexibility..... last forever.

but I still prefer sweating copper all the way.

edit: another thought....the copper pipes coming out of the unit could be far above the melting point. the heating element in the unit will have to have a very high heat source to get flowing water to raise 40 degrees. just my 2 cents

CPVC is not a good idea for any water lines. Yes, I know it's approved and rated. One of the main reasons I dislike it, is its toxicity. Not only when it burns(or melts!) but when it isn't doing anything!. The knock on copper lines was the leaching of the little bit of lead in the solder used for the joints. Do you really think that glue acts any differently? What about the chlorides in the pipe itself? A major project I worked on (for the gov't.)used PVC pipe for their water mains. The pipe is used throughout the industry and all over the country. But you have to sanitize the lines before they can be used to supply drinking water. This is usually done by the addition of chlorine, powdered or liquid, to the pipe while it's being put together. Apparently the Army corp. of Eng. who was responsible for overseeing this project, had water quality specs and the reaction of the chlorine with the chlorides in the pipe caused the water quality to fail. A lot of money changed hands and a lot of pressure was exerted before those water mains were accepted. --- Back on subject: I would hazard to say that the unit malfunctioned or glued joint failed. This happens when the proper primer isn't used or insufficient drying of the joint, or both. The glue and primer actually soften the pipe and fitting, which then harden. Being that you stated it was a Bosch unit, I wouldn't think the heater itself failed.

Is this one of those weird Bosch injection systems that modulate the fuel line pressure and the injectors are on all the time? Those things suck. If they are working, they are OK, but one little relay (of, what? Six thousand?) goes out, or some sensor and you are like totally screwed.

Otherwise, I'll go along with Grtechguy and mention that the thing is rated at 40 degree temp increase in running water. If you do the math, that's a lot of BTU's. How many amps/watts is the thing? I assume 220V. So, the heating element is going to be fairly large. Once it turns off, it will still have a lot of heat in it, and MAYBE that heat traveled up the copper outlet pipe to that plastic pipe joint and melted it. Just theorizing here. It shouldn't do that, so maybe the fuel pressure regulator is out of whack or the secondary fuel pump isn't working right. I hate those Bosch systems.

My theory would be that the heating element isn't shutting off, for whatever reason...

Check your water pressure to see if its too low for the spec, or check it with a meter to see if heat element shuts off based on demand...

Just my 2 pennies worth

Cool, thanks for the advice!

I'm leaning toward the idea of the heater not shutting off too. By my math, the total power would be somewhere under 8800-watts(220v x 40a breaker). It's certainly possibly I didn't get a good glue joint though(I'm not a pro plumber by any means), although I did let it cure ~45min.

As far as drinking the water, don't worry, no one in our town drinks the water. It's usually orange, and has high levels of lead & arsenic in it.

I chose CPVC because I like the smell. No, seriously, I find it easy to work with, and it seems like it's a bit cheaper than PEX still.

My parents had a similar system that worked fine for quite a while and then the reservoir tank suddenly burst about thirty minutes before they left for a week long vacation.

Complexity is synonymous with failure.

RX Reven' wrote: Complexity is synonymous with failure.

Montgomery Scott said "The more sophisticated the plumbing, the more places to stop up the pipe"

He also said "I'm giving her all she's got Captain !"

I am not a Certified Trekkie, so please refrain from sending Photon Torpedoes if I didn't get the quote exact !

Update:

I got another 1/2" copper -> CPVC adapter, specific CPVC cement(the orange stuff, not the clear), and put it back together last night. I let it cure a full 24-hours, and even set the power on the heater to the low setting before turning on the water, opening the faucet, then applying power(per the instructions).

The water coming out was just above room temp, which seemed about right for 1/2-power. I shut it off & walked around to check the heater on the back side of the wall & heard it gurgling even after the water was off. Before I could get to the breaker box, it popped the CPVC again right at the copper adapter.

So at this point, I'm thinking it's not shutting off, so I'll call their customer support # and see if I can exchange it.

Any chance of just using a braided flex connection(after the shut off valve) to the faucet? For that matter, you could even use compression fittings. Plumbing problems suck-especially where water is involved.

minimac wrote: Any chance of just using a braided flex connection(after the shut off valve) to the faucet? For that matter, you could even use compression fittings. Plumbing problems suck-especially where water is involved.

I'll agree with this as well.... you have, what a 4' run at most?

buy the flex lines and get rid of the plastic crap

+1. Terminate the hard supply line with a ball valve and a threaded adapter right where it comes out of the wall or floor (or the last elbow if the pipe is clipped to the outside of a wall. Run a braided stainless line to the heater. That pipe will be rated for hot water. Run another braided line out of the heater back to the wall with a threaded adapter.

Any way you can post a picture of the install?

Do you mean the normal braided line like for a toilet?

I could get some pics - but I'm almost ashamed to now, after redoing it 3-times(twice for the heater, the first for the original copper lines that had corroded all the way through) it looks like a horrible mess.

I'm surprised you've put up with this this long.

The unit is faulty. Regardless of anyone's opinion regarding CPVC, or the quality of the glue joint, the unit should never be heating the outlet water to a temp/pressure level where it could melt piping approved for this purpose.

Note, I said temp/ pressure rating. The issue is a combination of the 2. At 200F CPVC's pressure rating de-rates to approximately 20% of it's pressure rating at 70F.

The "pop" you are hearing is the pressure blowing out the piping/ fitting when the temperature gets too high.

The unit is faulty.

Don't fix this by using braided lines. Even if they work (and resist the pressure/ temperature), the unit is overheating, and you are risking a fire.

BTW- the melting temperature of CPVC is 395F. The boiling point of water is 212F. Safe temperature to avoid scalds is about 120F. Household water temperatures shouldn't really exceed 140F.

How high is your water pressure?

Thanks for the advice. I don't have a means to measure water pressure(unless I could rig my fuel pressure tester to the lines somehow....), but I've got plenty of water pressure.

Oh, and it actually melted it at the inlet, not the outlet, FWIW.

That's not better, it's worse. The unit shouldn't be heating the inlet side at all.

Is the pressure abnormally high? Like, do you notice the difference when you are washing your hands compared to other places?

Doesn't really matter- the unit is faulty.

Wait- Any chance you wired it like it was 110V?

It's only configured to be wired one way since it's a 220v model. I bought a new 40a breaker & ran new wiring to it, so I'm not sure what could be wrong on that end.