We're in hot water!
July 25, 2022 8:38 PM   Subscribe

Hot water comes out of the taps in our house, even when they're turned to cold. If we run the water for long enough, it eventually gets cold...but we live in a drought, and I hate wasting water. Sometimes the water is so hot it hurts our hands. Why is this happening and how do we fix it?

Possibly relevant info:
- The house is in California, and it's over 100 years old.
- We remodeled extensively 8 years ago. We installed two big hot water heaters then.
- The problem is happening with both old and new faucets, including one that had the cartridge replaced recently.
- The plumber who did the renovation was bad at his job and caused a lot of problems. We learned afterwards that he had an unlicensed crew doing most of the work. Over the years, we've had to fix a number of things they did wrong.
- The problem has gotten bad over the last couple of months. It seems to be happening simultaneously with all of our taps. Before that, only one sink had this problem, and the rest had cold water anytime we wanted it.
- The only thing that has changed with our water system lately is that we installed an outdoor landscaping watering system a few months ago. I'm assuming that wouldn't affect the temp of our indoor water.
- We have an old recirc system that is programmed to go on at certain times of the day.
- A new plumber came and looked at our system and said he wasn't sure what was wrong. He said he could spend a few hours trying to figure it out, but there was no guarantee he could find a solution.

Maybe you have experienced a similar problem before? Any insight would be helpful!
posted by equipoise to Home & Garden (20 answers total) 1 user marked this as a favorite
Could there be a bad hot/cold faucet valve somewhere, allowing the hot water to flow into the cold pipes through a temperature inversion?
posted by nickggully at 8:41 PM on July 25, 2022 [3 favorites]

Do any of the pipes go through areas that are typically hot in the summer, like through an attic or somewhere else exposed to the sun? We had to repipe our house due to bad plastic pipes (long story), and the incoming lines go through the attic, where the water heats up when not being used, causing cold water faucets to run warm at first.
posted by TimHare at 8:45 PM on July 25, 2022 [16 favorites]

As part of your remodeling, did the plumbing switch from rigid pipe in/under your concrete slab or other pipe that ran through conditioned space to flexible PEX plastic pipe in an unconditioned attic?

On preview: what he said!
posted by RichardP at 8:45 PM on July 25, 2022 [4 favorites]

You could test between the two hypotheses so far -- crossover from the hot side, or external heating -- by shutting off the output from the water heater.

(External heating of the water in the pipes sounds simpler to me since the water heater shouldn't be keeping pipes hot up to the taps unless water is moving. But when plumbing is really messed up, it defies logic...)
posted by away for regrooving at 8:57 PM on July 25, 2022 [5 favorites]

Does the water run hot very early in the morning (when your entire house, including the attic, has had a chance to cool down)? Or in the winter for that matter? If so, that seems like it rules out the idea that the pipes are heating up.
posted by caek at 9:14 PM on July 25, 2022

Best answer: Start with the easiest troubleshooting step, even if it probably isn't the cause of your issue: turn off the recirc system and see if that helps. Ideally, if there's a valve inline with the recirc pump, close that entirely.
posted by ssg at 9:17 PM on July 25, 2022 [3 favorites]

I too wonder if the problem exists first thing in the morning.

My water system behaves much like yours but it is expected because a lot of it is on the roof.
posted by Tell Me No Lies at 9:32 PM on July 25, 2022

Best answer: The recirc system's job, in some setups, is to pump the cooled water from the hot water pipes into the cold line. If it's being overenthusiastic it might be pumping actual hot water into the cold line. I would turn it off for a day or two, and, if that turns out to fix it, run it for less time.
posted by How much is that froggie in the window at 10:02 PM on July 25, 2022 [2 favorites]

It sounds like you have a circulator. Our house was built with one, the idea is you have instant hot water so you don’t let the shower run. We can turn ours off during the day and just turn it on in the morning when we shower. If we don’t turn it off we have exactly the issue to describe.

If that’s it, you’ll see an extra circulator attached to your pipes somewhere. You should be able to turn it off.
posted by ohio at 11:19 PM on July 25, 2022 [1 favorite]

You have some good suggestions above, but since it hasn't been mentioned yet, make sure that your outdoor landscaping watering system has backflow prevention. Without something to prevent backflow, water in the watering system can be pulled back into the house. Not a high chance of this happening, but best to rule this out.
posted by jraz at 5:15 AM on July 26, 2022 [2 favorites]

Best answer: Maybe the landscaping water is partially being pulled out the cold side of the water heater, which means you are pulling hot water into the cold water lines. This is easy to check, one water heater will have the input cold pipe be very hot. Prior to this, water was slowly circulating between the two water heaters; are they at slightly different heights?

If not that, the recirculation pump is using the cold line to return hot water to the tank. Because you have two tanks, it found another path to travel and is heating up all the cold lines.

Either way, if disabling the recirculation pump doesn't solve the problem, you need to add check valves to *both* of the water heaters.
posted by flimflam at 7:30 AM on July 26, 2022 [1 favorite]

You have some good suggestions above, but since it hasn't been mentioned yet, make sure that your outdoor landscaping watering system has backflow prevention

If you were able to get one installed without a backflow preventer, I'd be surprised. And if you don't have one it's an expensive fine. Most sprinkler systems have a second line (generally larger) coming off your meter- they don't use your house line.

Hot and cold water piping is completely separate, so I'd blame your recirculator too. Turn that thing off - they are serious luxury and completely unnecessary.
posted by The_Vegetables at 7:34 AM on July 26, 2022

It’s also possible that your hot water lines are not insulated, and are right next to the cold water lines, and thus heating up your cold water lines.
posted by rockindata at 7:58 AM on July 26, 2022 [2 favorites]


It definitely shouldn't happen frequently, but you'd be surprised. I've worked at 4 different water utilities over the last 30 years and I still am shocked at the amount of unpermitted/illegal stuff out there. Lots of unlicensed folks and the DIYer's.
posted by jraz at 8:29 AM on July 26, 2022 [2 favorites]

It definitely shouldn't happen frequently, but you'd be surprised.

Oh yeah, I believe it happens, but the fine for not having one where i live is $10k, so I'm saying to the OP if you did unlicensed sprinkler work, be very careful.
posted by The_Vegetables at 8:47 AM on July 26, 2022

Best answer: recirculation setups that push the hot water back into the cold side have a thermo-sensing valve which can fail. If it fails open, the circulation pump will always be pushing the hot water to the cold side.
posted by soylent00FF00 at 3:16 PM on July 26, 2022 [2 favorites]

When this happened to me it was because of a slab leak. The hot water pipe had a leak and had heated up the slab surrounding it to the hot water temperature. The cold pipe was in the slab too and was therefore heated up by the leaking water. I found the slab leak due to an unusually warm spot on my floor. I live in an old building too and slab leaks are not uncommon in that kind of situation. One thing to check is if there have been any big changes in your water use lately.
posted by kms at 12:09 AM on July 27, 2022

Response by poster: I'm really grateful for this help! Our pipes don't run through our attic -- they go straight from the basement to the two floors above it. The landscaping work was done by licensed professionals with a permit, although that doesn't mean they did a perfect job. We have turned off the recirc, and I haven't noticed the hot water problem since then, so we'll keep monitoring it. I'm hoping soylent00FF00 is right and it's just a matter of replacing the recirc valve. Thank you all so much!
posted by equipoise at 1:02 PM on July 27, 2022

There is some sort of crossover between the hot and cold sides of your plumbing. This can be caused by the incorrect installation of a water heater, but the recirc valve would also do this if it was stuck open or leaking somehow.
posted by dg at 7:16 PM on July 27, 2022

Response by poster: With the recirc off, the problem is gone. And it doesn't seem to take any longer to get hot water than it did before! So we'll keep it off for now, and if hot water becomes too slow in the wintertime, we'll look into replacing the recirc valve. Everyone who suggested turning off the recirc is better at troubleshooting than a highly recommended, licensed plumber who inspected the system in person, and you saved us $100s of dollars. Thank you!!
posted by equipoise at 1:01 PM on August 6, 2022 [1 favorite]

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