I'm stumped. Hot water not staying hot...

I've been trying to figure out an issue with my Mom's Las Vegas condo involving the hot water. She's lived in the condo for over 20 years with very few problems with anything over the years. Recently, we found that the hot water coming out of ALL faucets and shower mixers will start out hot and slowly become cooler and cooler. I'm a DIY guy with very little plumbing experience so I started researching online. Since it was affecting everything I started with the hot water heater. It's seven years old, very hard water in her area and had a water softener in the system for part of it's life. I decided to replace it but there was no change in the hot water problem afterwards.

Hot water slowly gets cooler...
- new hot water heater, water gets very hot in tank.
- water softener was removed a few years ago with a bypass line.
- Condo uses a ThermoAir (sp?) heating unit that works great, all lines get hot.
- Four sinks with single handle mixers.
- Two showers with single handle mixers.

What I've tried...
- Turned every sink faucet on individually on hot with full volume. All stay hot for a minute or so and start to cool down.
- Turned all sink cold water valves off and tried the same thing with same results.
- Turned shower faucet on full volume full hot and IT STAYS HOT.
- Turned sink faucet on hot and let cool down. Turned shower faucet on full hot while sink faucet is still on and sink faucet got hot again.

I'm stumped, but it seems like cold water is mixing with hot water somewhere and if you have enough volume on the hot side it stays hot. As soon as the hot water volume goes down it allows the cold water to affect temp.

That's my guess, I don't know enough about this stuff to go forward other than replacing both shower mixing seals to eliminate them as the problem. Nothing has changed around the time the issue started happening.

Dan

After reading other posts here I'm wondering if I should just change the mixing valves in the showers and see what happens.

Not sure what kind of faucets you havve single handle or 2 hanle i have experienced a single handle causinf hot and cold to crossover
The way a found it was to leave all the hot water on and isolate only tbe sigle handles oe a tme

Yes, it sounds like there is a failed cartridge or pressure balancing unit, or both, in one or more showers.
So cold water is leaking into the hot line through a valve or cartridge, even if that shower is turned off.
Or hot is leaking out into the cold line.

A cross connection can happen inside, at a faucet or shower that seems to be working ok.
So Geofd is right, it could be at any faucet or shower.

As a test, right after a shower you can run some cold water at a faucet, or flush a toilet, and feel the water temp or just feel the shutoff valve, for being abnormally warm.

FYI the cartridges are often guaranteed, if you know the brand or can post pics, someone here will likely point out the brand and model of cartridge.

Geofd said:

Not sure what kind of faucets you havve single handle or 2 hanle i have experienced a single handle causinf hot and cold to crossover
The way a found it was to leave all the hot water on and isolate only tbe sigle handles oe a tme

Click to expand...

I changed out thethe cheap contractor grade faucet to abullet proof chicago two handle

Thanks guys, you gave me more confidence in the shower crossovers being the issue. I turned off all the faucet cold water valves during my testing and it still had the problem so it has to be the showers. Progress!

e9coupe said:

Thanks guys, you gave me more confidence in the shower crossovers being the issue. I turned off all the faucet cold water valves during my testing and it still had the problem so it has to be the showers. Progress!

Click to expand...

Try shutting of 1 fixture at a time let all the faucets run and only the cold then check the remaining running faucets.after you test all faucet
Then test knly the showers
you have not said if all or none of your faucets ar single handle isolate only the single handle faucets when testing

Has to be Moen faucets. sink or tub. As stated, if you are the original owner, Moen will supply cartridges for free. Call CC.

Friend had this problem in her new house, after new water heater, and 4 different plumbers, turned out to be the Moen shower cartridge.
(Which is another reason I like Delta's design.)