domestic hot water issue

nytech28

got a call on Sunday landlord saying he gets hot water in his faucets for few seconds & then turns cold on 3rd flr apartment  , he checked the  D- hot water tank to make sure it's working & it's fine  , any idea what could be going wrong with 3rd flr not getting sufficient heat to the faucets  , I haven't seen the job yet.

Larry Weingarten

Hi, I'd be looking for a crossover between hot and cold, or a recirc line that doesn't have a working check valve in it. First test is to shut off the cold supply to the heater and then open a hot tap. If it doesn't stop running pretty quickly, cold is probably getting into the hot side. If that is okay, turn on the cold supply to the hot water, open a hot tap, and feel the recirc line where it connects to the tank. If it cools off, you know cool water from the bottom of the tank is running backwards through the line.

Yours, Larry

nytech28

ok I will test what you described,but i feel that there is no recirc- line or recirculation pump if that's what your referring , 2 pipes on this tank, cold water in & hot water out with city pressure .

Mad Dog_2

Hot & Cold water sandwich....Is this a Tankless Water Heater?   Mad Dog 🐕 

nytech28

it's a  basic tank that holds 40-60 gallons of water .

Larry Weingarten

Hi, That limits things to a crossover, though I'd still do the test. Do you know what brand of faucets and shower valve are in the unit? Some older cartridges can allow crossover. I'd also check to make sure they didn't add a shutoff valve on the shower arm, or some-such.

Yours, Larry

ps, is there a tempering valve installed?

Intplm.

Seems like a cross-connection of some sort as mentioned previously.
You will need to investigate any changes in the plumbing system. And I mean any changes, like a hose connection wye connector installed at a sillcock or laundry. Or a shower valve or faucet that is crossing the hot to / cold to hot?
A failed or failing check valve?
This is usually something that is easily overlooked and not thought of as significant.

nytech28

will check them, aprecaite the time & info

Mad Dog_2

We find Commercial type T & S Brass Kitchen sink Faucets will allow a Cross-connection if the little spring checks fail.  Mad Dog 🐕 

nytech28

ok i.ll check then out thanks