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Whole house: water either too hot, too cold, or sometimes just right

Appreciate in advance any ideas anyone might have... we have a laundry list of issues so apologies for the long post, but here goes...
House is 25 yrs old, 2.5 bath, single level, in Arizona with hard water. HW tank looks original with no obvious leaks (was last flushed 5 yrs ago); there is a recirc pump and expansion tank under kitchen sink with timer attached and a spring wound wall timer. Home has been vacant for 2 years (Covid) with HW tank set to vacation mode and main water still on. No previous problems with hot and cold water temps until now. We finally got to visit the house a few weeks ago for a week.
Day 1: turned up HW tank from vacation mode in the evening to regular use notch. Ensuite shower was scalding hot at night even when turned completely to cold. Turned HW tank down a notch.
Day 2: washing machine broke (door wouldn't unlock), so we bought and installed a new (used) washing machine. Too busy sorting out washing machine to deal with shower, now running semi-warm even when set to hot. Turned HW tank back up to regular use notch.
Day 3: guest bathroom sink (2 handle faucet) cold water was warm in the morning, ensuite shower was scalding hot. Assumed it was us mis-setting the dial on the HW tank. Plumber came to install replacement water softener (Rheem 40,000 from Home Depot... don't hate on our big box choice, we needed one immediately)., and noticed laundry sink cold water was running hot. He said it was defective so replaced existing 2 handle faucet with a new single handle faucet. It still ran hot. Plumber said he could hear occasional little sounds in HW tank (I couldn't hear anything) and suggested replacing tank and installing recirc pump above tank with sensor valve under kitchen sink. He didn't want to touch the HW tank to drain it because he said the plastic drain valve might crack.
TBH, I had no idea what all the spaghetti under the kitchen sink was. I think that recirc pump has never worked in the 10 years we've owned the house. There is an RO system under the sink as well. It's spaghetti junction under the sink, so I left it alone. I now see a recirc pump with timer dangling under the sink. There is a spring loaded timer on the wall above the counter. Turning the timer to count down doesn't make anything happen... no humming, running, etc. The expansion tank has no obvious leaks or stains on it.
Day 4: guests arrived. Main bathroom shower runs ice cold for morning showers, then warm an hour later, then just right; laundry sink runs cool in the evening; kitchen sink runs cool through the day; ensuite shower runs scalding hot then cool then scalding hot; toilet bowl feels warm to touch.
So hot water sometimes runs cold, cold water sometimes runs hot, and sometimes it all works.
We're not at the house now so I can't take pictures. I've tried reading up to find someone else who's had this happen, but can't. Any ideas what's wrong or where to start looking? Thanks in advance for any comments.


  • Jamie Hall
    Jamie Hall Member Posts: 22,212
    You may not know, but I'll ask anyway -- is there a mixing or tempering valve on the output of the hot water heater? If so, I'd bet at least a doughnut that it's sticking. No use for two years? Wouldn't surprise me at all.

    Second place to look is the recirculation system. They often have check valves in them which can stick open, leading to some very odd problems (some of which are like yours). If there's a way to valve it off completely, do. You clearly don't need it.

    Third place to look is at any single handle faucets -- the mixing kind. Again, no use in two years? Wouldn't surprise me at all if they were sticky or just plain stuck.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,143
    Hi, It’s time to do a crossover test. This is a way of knowing if cold water is inadvertently getting into the hot lines or visa versa. Shut off the cold supply to the heater and open a hot tap. Water should stop flowing in a few seconds. Let us know what you find. ;)

    Yours, Larry
  • Clooless
    Clooless Member Posts: 7
    Thank you so much for the replies, both of which are greatly appreciated. i will be back at the house this weekend and will check or try to check for:
    1. mixing or tempering valve on output of HW tank
    2. check valve in recirc system
    3. single handle faucet crossover
    4. crossover test, as per Larry above
    I decided to post this because I can't find a plumber who has an idea of why this is happening. I chose not to continue with the first plumber who installed the water softener as he was quite surprised by the hot water coming out of the cold side of the existing 2 handle laundry faucet; he replaced the faucet, the problem continued, and he just left. I phoned around looking for another plumber. One honestly said he had no idea, another said he would maybe cut some walls to check some pipes, and a third said you can have hot turning cold or cold turning hot but not both and I must be mistaken.
    I am just so very grateful for your replies, and will post when I'm back at the house.
  • Clooless
    Clooless Member Posts: 7
    I cannot find any valves on the HW tank. Anywhere.  Please see pics.  
    There is a good amount of white calcified buildup on the connections on both of the pipes toward the back of the HW heater. Apart from that, I don’t know what else I should/should not be seeing. 
    I’m thinking there should be a way to turn off the hot water coming into the house but I can’t see how. 
  • Clooless
    Clooless Member Posts: 7

  • Clooless
    Clooless Member Posts: 7
    The recirc pump under the sink was switched to the off position. I turned it on and it began to run. For good measure I pushed all the pins and turned the wall timer on to 60 mins as well.  It’s been 15 mins and there is no effect on the water temp issues. I didn’t expect there to be though. And great, it’s taken me 10 years, but now I know I have a recirc pump that powers on!  Considering it wasn’t on before though, I don’t think the recirc valve is the issue…
  • Clooless
    Clooless Member Posts: 7

  • Lance
    Lance Member Posts: 257
    First, if your water heater gets hot and stays hot even when running a hot water spigot cold, the heater is not the problem. There is a piping problem causing back flow which can happen when a recirc system is built wrong or a check valve fails, or a hot and cold pipe have been reversed. A mixing valve, or internal spigot can have a flow issue between hot and cold when both are on. Also if a mixing valve is installed, it can fail like your symptoms described. Piping may need to be traced. Test only one fixture at a time. Isolate the recirculate loop when testing for cross connections. Flows can change randomly when pressure and temp controls adjust. Ask for a Master plumber with experience when faced with results of failed results. Verify his license and insurance to be sure. Best of luck to you.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,143
    Hello, That corroded, blue handled thingy on the cold supply, above the heater is the shut off valve. It's a gate valve, which are notorious for breaking if they haven't been used for a long time. Also, it's soldered into place, which makes it "fun" to replace when it breaks. I'd shut off water to the house and either unsolder that valve or cut the line before it and install a copper male adapter so a threaded ball valve can be screwed into place. Once you have a decent valve, the crossover test can be done.

    Yours, Larry
    ps, While at it, I'd also solder a male adapter onto the hot side pipe coming from the wall so you can replace both of the copper flex connectors.
  • Illinoisfarmer
    Illinoisfarmer Member Posts: 50
    It looks like there's a check valve in that circulating pump that is supposed to keep the hot water from bypassing to cold when the pump is off and vice versa. The diagram is on page 1 of the owner's manual. I'd unplug the pump and try shutting the valves under the sink that go to the pump (and sink) and seeing if that isolates the problem.

    Owner's manual:

  • Clooless
    Clooless Member Posts: 7
    Illinoisfarmer you rock!!! You pinpointed the defective valve ahead of the plumber arriving today... I unplugged the recirc pump and the water temp issues corrected immediately... hot water from hot faucets and cold water from cold faucets, and, better yet, no more than a few seconds wait for hot water from furthest bathroom!!!

    Certified plumber is here now:
    1. Install Ruud 50,000 HW tank (6 yr warranty) with ball drain valve including hose bib fitting
    2. Install ball valve shutoff for cold water supply to HW tank
    3. Replace non-working TP valve and current non-code flex piping to new TP valve with up to code piping
    4. Seal CO vent to prevent any leaks
    5. Remove recirc pump under kitchen sink (can add Grundfos recirc pump above HW tank later if needed)
    6. Install new hot and cold water shut offs under kitchen sink, and new flex piping
    7. Install new RO system to replace 20 yr old current RO

    We will have to eat mac and cheese for at least the next 3 months to offset the cost of all this, but we will have peace of mind knowing our plumbing issues are resolved.

    Thank you to each one of you for your invaluable input. I greatly appreciate all your support and kindness, and am humbled by the wealth of wisdom you all have to offer.

    Merry Christmas to you and your loved ones!!!