Low Water Pressure/Volume After Instant Hot Water Valve Installed
January 2, 2020 5:26 AM   Subscribe

We got a new water heater a few months ago. They sold us on two valves to have instant hot water in the two master bathrooms. One is on first floor, the other is on second floor. The first floor has the same volume/pressure as before. The second floor has low water volume/pressure at the faucet and shower after the valve. Help me get a great shower again!

We have a jack and Jill sink in the bathroom. The one before the valve is the same as it was before the new water heater/valve. The valve is installed between the two faucets. The faucet after the valve has low water pressure/volume. This was not an issue previously. The plumber came out once and he cleaned the faucet and shower head, saying that debris sometimes gets in line when installing a new WH. My husband check to make sure the water was back to normal. It wasn’t. We had them back out again, they say that it can’t possibly be the valve as they have never had that happen. Not that it shouldn’t happen, they just haven’t had that happen. They say I must have “weird plumbing” and he wants to rip out my wall to have a look.

The first floor bathroom does not have this issue.

Is this a problem that can be fixed? What can I call tell them to look at? I had a fabulous shower before the new water heater. Anyone have input on if there is something wrong? Did they do a bad install or maybe need to do a revision? Help me have a good shower again.
posted by bodgy to Home & Garden (3 answers total) 1 user marked this as a favorite
I guess I’m unimpressed by “we’ve never had that happen” since I’ve heard that so many times over the years by so many obvious liars. I would say “well, it’s happened now, and you need to address it.” I would start by discussing it with the owner if you haven’t been talking with them already. Buck-passing isn’t a good look for a business that depends in large part of good word of mouth. Remember that once you make it adversarial, you can’t go back, though.

You might call the local building-code-enforcement people and ask if they’ve ever heard of this problem. Plumbing is not really rocket science. If there is low flow, then there is some kind of restriction, and since they just added a restriction, that’s kind of where I’d focus my first suspicions. How hard would it be to get at this valve to see what happens if it’s removed? Ripping into walls can be pretty expensive and if it turns out to have been unnecessary, I’d want a previous agreement about who was going to bear the cost. Good luck. A good shower is worth some trouble (and expense).
posted by Gilgamesh's Chauffeur at 6:23 AM on January 2, 2020 [2 favorites]

Response by poster: I can get to the valve. I’m not sure which knob to turn but I will play with it. It’s programmed electronic to circulate in the morning. It’s still low flow/pressure outside of those times. I completed to the other side of the sink. It looks like they added extra piping for this.

I’ll get adventurous tonight and see if I can turn it off and if that makes any difference.
posted by bodgy at 7:06 AM on January 2, 2020

Best answer: If that were my house, I'd be having them take the instant hot water valves back out and put things back the way they were.

Those valves allegedly save energy "by stopping your hot water pipe from cooling down" but in fact doing that very thing is only ever going to waste energy, not save it. If you have a tank full of hot water sitting there all snug inside its inbuilt insulating blanket, and then you add something to your plumbing that allows water from the tank to circulate through the (usually non-insulated) pipe between the tank and the furthest outlet, then all you're doing is providing a way for the circulating water to carry heat out of the tank and let it escape into the air around the pipes.

All the obfuscatory remarks in e.g. Hot Water Lobster's promotional material about dumping a pipeload of cold water down the drain every time you turn on your hot tap can't change the fact that the effect of their product is almost identical, thermally, to leaving a hot tap cracked open to a trickle all the time.

As for the claimed water savings: well, how much is a pipeload, anyway? For a back-of-the-envelope rough idea, let's take the internal diameter of the water pipe to be half an inch; say 13mm. Then the cross-sectional area will be π/4 times the square of that, say 130mm2.

A square millimetre times a metre is a millilitre, so each metre of pipe holds 130ml of water, so a 20 metre run holds two and a half litres: about quarter of a bucket. And I would expect your heater to be rather closer to your furthest shower than 20 metres unless your house is exceptionally poorly designed.

What these devices will do is give you warm to hot water at the showerhead a few seconds faster after turning on the hot tap than you'd get without them, which is kind of luxurious, maybe? And yes, they will stop your hot water pipes from freezing solid, but if that's ever been an issue for you then the correct fix is insulating the pipework, not wasting energy on actively warming it. On balance, I have them firmly filed under "crock".

Putting two of these things in a house is weird as well, unless your two bathrooms are on completely separate supply runs all the way back to the hot water tank. My immediate inclination would be to distrust the honesty or expertise or both of whoever sold you this configuration.

That said: I can see no way that having a new thermostatic valve installed between hot and cold supply lines, which is where these things go, is going to cause pressure or flow rate issues in the lines downstream of the point where it's installed. That would require a restriction within at least one the lines. So if you're seeing pressure issues since installation that weren't there before, there must now be such a restriction, which means that the installation has been done badly; perhaps somebody's apprentice got a bit keen with the thread sealing tape and accidentally wrapped some over the end of a fitting before screwing it home?
posted by flabdablet at 7:10 AM on January 2, 2020 [6 favorites]

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