Are you sure the inlet and outlet are correct? There is no way you could melt the inlet... that's supposed to be cold water. How do you melt plastic with cold water? like SVex stated, it shouldn't be heating the inlet side at all. READ THE DIRECTIONS. Not being a smart ass, but if it's piped correctly and wired correctly, it has to be a faulty unit.
Thanks, yeah I've been through the directions numerous times. I called Bosch's help line today & was surprised someone answered. He proceeded to tell me I needed 3' of copper in & out of it and I said "you really should update your instructions then, since it says to keep the runs as short as possible"...he went on to tell me that he wasn't actually a tech & I should call back Monday. 
Plastic water piping of any kind(PEX, PVC, CPVC) can't be installed within 18" of a water heating device, except for discharge tubes tied to safety relief valves. You need to transition to copper at least 18 inches away from the unit on both hot and cold water lines, and then tie into the water heater with copper. This code requirement is to prevent what happened to you. You will also need to tie in a temperature and pressure safety relieve valve. If for some reason the heating element continues to heat, you will superheat the water in the unit building pressure. At somewhere near 300 PSI, it will rupture and the superheated water will flash to steam and expand it's volume by over 1800 time. Can you say BOOM! Ever see the Mythbuster episode where they blow the water heater? The safety relieve is designed to prevent this from happening. It will allow water to dump out of the heater thru the disscharg tube.
petegossett wrote: 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.
"gurgling" = "on" and boiling water despite there being no flow
i'd say the flow switch is sticking closed and causing your problems. check for a current draw or voltage across the element after you shut the water off.
not to scare you, but i have seen an example of this very brand of unit that has actually caught fire and then self extinguished when the plumbing circuit became breached. on the other hand, i have the same unit in my shop (also from menards) and it works fine (so far). it is nice to have warm water in the shop.
Dumb question: Is yours all plumbed with copper?
petegossett wrote: 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.
No. there are braided lines rated for hot water and use with heaters. I have them on my heater. CA mandates flexible couplings with tank hot water heaters and the copper flex pipe fails during earthquakes. Yes I kinow you're installing a tankless but the rating is the same.
In reply to petegossett:
It is plumbed in copper except for the 1/2" npt connections to the unit. There I used some type of "Sharkbite" or other quick disconnect tube-to-npt fitting (only for easy disassembly if needed, no earthquake provision necessary). However, the inlet and outlet tube temps should be nowhere close to approaching the temp rating of either CPVC or PEX tubing. It is common to install a water heater with CPVC to npt adapters right at the top of the tank. This thing is only supposed to be making domestic hot water (140 deg max.) on an on-demand basis. I still think it's sticking "on."
petegossett wrote: 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.
That's not really a good enough answer to my question.
No offense. Have you put an electrical tester on it?
It IS possible to install a 220v unit with a 220v breaker but wire it incorrectly in the panel box to be delivering 110v power on one leg, with the second hot leg being used as a neutral. Guaranteed way to have fouled results.
This wiring (of the breaker in the panel box) would NOT show in the instructions.
In "normal" wiring scenarios:
-If the wiring from the unit to the panel box has 3 conducters plus a ground, it should be wired R=hot, B=hot, W=neutral, Bare= ground.
-If the wiring from the unit to the panel box has 2 conducters plus a ground, it should be wired B=hot, W=hot, Bare= ground.
-If the wiring from the unit to the panel box has 2 conducters plus a ground, and it is wired B=hot, W=neutral, Bare= ground, then it will deliver 110v on one leg. This shouldn't work at all, but on some units it could increase the resistance in the heating coil.
Check the wiring with a meter.
I still say the unit is faulty. Even though, as some of the previous posts note, copper piping SHOULD be used within 18" of the heater, it still should not be heating the piping to the point of melting. The 18" thing is good practice. In reality, heaters are piped all the time with CPVC attached directly to them.
ohioboy:
Are you and petegossett the same person? I'm confused.
You'll need to log in to post.
