Adventures with external-storage hot water

SpeyFitter

This last summer I'd posted here about using a 40 gal. electric water heater as a storage tank for my tankless coil (1-pipe steam, oil-fired Burnham boiler, Taco 006 circulator returning through the drain valve port). It's been working great since July, except for a tiny seep at the bottom of the tank where I hadn't screwed the fitting into the drain port tight enough.

So over this weekend my hot water started getting way too hot for the first several gallons. The relay wasn't stuck and in fact the circulator pump was not even running. I figured out that the check valve had to be stuck open so it was thermosiphoning backward through the coil and circulator. Heat has been on a lot lately when it's -15F outside (has been as low as -25F) so that coil gets really hot... Sunday it got hot enough to trip the tank's overheat reset, so after the initial scalding blast the water then got ice cold (fun in the shower for a Maine winter). Examination showed a significant new leak at the *cold* inlet port where the CPVC line threaded in. Pressure/temp relief valve never vented, fortunately.

So I had to fix it. Sure enough, check valve had quite a bit of fluffy white deposits (almost looked like melted styrofoam pellets, which maybe it was if it got into the heater from the foam packing) and a blob of solder which was probably keeping the flap from closing. Cleaned that up, went to the box store and got some different fittings, replaced the first two feet of the cold inlet with copper. While the system was "down" I also decided to fix the little drip from the bottom port. Added a 6" nipple, Teflon taped the threads and tightened it securely, then a brass female-female coupler over to the output of the coil. Turned on the water - leaking from the coupler. Tightened it a bit more, leak got bigger. @#$%. Shut off the cold valve, leak stops. Another quick trip to the hardware store.

So I replaced the (apparently fragile or flawed) brass coupling with a female-threaded copper sweat fitting, (very little water came out with the vacuum holding it up). Water back on, so far so good. Hit the switch to start the circulator pump - when the hot water entered the cold tubing then a squirting leak started in one of my solder joints! @#$%^^&*&*!!

By then it was time to head over to friends for dinner, got home at 9 PM, back to the basement, fixed the leak properly (took my time, got everything good and dry and fluxed). Finally everything working again.

I put a box-store "Hecho in China" (that's what it says!) 0-100 psi gauge on the cold input to the tank. With no flow it says 94 psi. With a hot faucet wide-open, 76 psi. Even allowing for a cheap gauge inaccuracy this seems high. Should I have a pressure limiter from the street line? Who installs that, a plumber or the utility?

-Charles

John Starcher_4

I wonder.....

...if that's the "street" pressure, or if you're seeing an elevated pressure due to thermal expansion??? You need to check the water pressure on a cold line, upstream of the water heater, and with the tank cool. A pressure regulator is almost always a good idea, but you really should consider installing a potable rated expansion tank, too.

SpeyFitter

I have one...

A 4.5 gallon expansion tank, that is, teed into the cold water inlet to the heater. But thanks for the reminder

(The previous "professional" had not provided any means of expansion for the tankless coil, so of course the pressure relief valve was always weeping).

If, for example, the expansion tank was depressurized and filled solid, I agree that the pressure might indeed rise quite high from thermal expansion. But letting some water out and closing the tap would have relieved that hydraulic pressure instantly, and the gauge always returns to 96 psi immediately, whether the boiler is running or not.

So is the homeowner or the utility responsible for providing "normal" pressure, whatever that may be?

thanks
Charles