Question about Rheem Tankless Hot Water Heater Rtg-74pvp-2 7.4 Gpm

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When hot water is on & toilet flushed the temp drops

This just started last month, before you could have the shower & a faucet going & flush the toilet and the temp would not dip.

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  • dajhomework Jan 06, 2009

    The pressure does not drop the temp does. It is like the heater just stopped working but once the toilet stops or other faucet it turned off the temp comes back up. the unit is about two years old.

    I have a filter on the supply from the street & a pump to keep the pressure up you can have about 4 things going before the pressure starts to drop.

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Check strainers and screens into the sink, at the spout and into the hot water heater. Sediment buildup could be limiting the flow which woul make the system more susceptible to pressure drop when the toilet is flushed.

Posted on Jan 05, 2009

  • Tripp REa Feb 10, 2009

    Its not the temp from the water heater. Its an imbalance between the hot and cold pressure going through the shower valve which is resulting in more cold than hot getting through the valve. No way is the water temp from the heater arbitrarily dropping in correlation with the toilet flush.

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Water does not stay hot it is uneven in shower, from cold to hot then hot to cold


Ok that sounds more life a faucet that is bad. In today world, the newer (20 years and less) they have pressure balance faucets. Have the faucet serviced. NOW lets look at an other area check out your home to see if you have a cross connection. A cross connetion is a place where hot and clod water meet. I know that everywhere but the toilet!

Yes thats true. But we buy all kinds of things that we attach to a fauects or tub spouts. Lets say you attached a hose to the sink in the garage to wash the dog with warm water. if you turned the water off at the handle of the hose and you left the water on at the faucet. BINGO

the hot and cold water mix and then up and down water temp while taking a shower.

So start looking first before spending any money. if ANYTHING is attached to any faucet take it OFF and then take a shower.

Be safe

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well it is time to get the the two way valves to both side, I would use only a product the noritz says to use.

Now if you cant get it you can get other products that break up lime and scale from you local store that sells plumbing product. I you can see I dont list a store or a product I am here to help you repair your heater, Not have you buy from one store or an other.

With that being said you can vinegar but dont use acid. If yuo "burn" the inside of the heat exhanger you jusy might be buying a new unit. also Please flush out the system with cold water for at least 10 mins. with the 3 way valves that should be very easy to do.

You also might have a lime build uo in the faucet also which will affect how they work. You may want to replaced and cleanout the cartridge and see if you have a lime build up. If that is the case you might want to think about a low priced water filter or softener.

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