Help!! Rheem tankless water heater not producing hot water

[mzafar]

Hello,
We have a Rheem tankless water RTGH-95DVLN-2 that was installed about 7 months back. Since start of winter we have not been getting water to stay hot for more than a minute or so. It is more noticeable in the shower. When the faucet is turned on we would get hot water for a minute or two max, and then it would turn lukewarm to eventually cold. This is the case with just one faucet running. We have a recirculation pump with a grundfos valve. There's also a Culligan water filter attached to the unit (Pics attached). Tried changing the water temp to 120, 125 & 140. Water would stay warmer a little longer at 140, but it would eventually turn cold. Changed all the shower cartridges. Tried turning off flow to the grundfos valve to rule out issues with recirculation unit/grundfos valve. Nothing has worked so far. Would appreciate advice on what could be wrong and what needs to be done to fix this issue.
Thank you!

 

[GReynolds929]

Couple quick unrelated observations from the pics posted. Without neutralization the condensate from the water heater will corrode and eat away the metal drain pan within a couple of years. It looks like your pressure relief has been opening. With recirculation there needs to be a tankless thermal expansion tank installed to mitigate thermal expansion pressure.

In regard to the temperature issue it sounds like there is cold water entering the hot system. There should be a way to monitor the outlet of the water heater. If it maintains temp there then crossover happening somewhere else. If the water heater is not able to maintain temp at the outlet there is cold crossover in the tankless. Should still under manufacture and installer warranty for parts and labor. I would have the installer back to troubleshoot and fix while under their warranty

 

[breplum]

Call original installer. Is there a piping diagram from the mfr showing a check valve ?

 

[mzafar]

@GReynolds929 & @breplum thank you for your responses. I'm sorry, I'm the homeowner, I don't have enough knowledge to answer your questions. I had asked the installer to come over & take a look. He stopped by twice and said the cold water was mixing with hot water outside the tankless water heater, and asked me to change all shower cartridges, which I did. But the problem persists.
Also hired a plumber on thumbtack who said it was a flow problem with the water heater and that I need to get it descaled. Installer vehemently disagrees with this and said the Culligan filter was installed just so it can prevent scaling. I'm at a loss as to what needs to be done.
If the problem is due to hot water mixing with cold, how do i troubleshoot it further?
Thank you!

 

[GReynolds929]

Turn off the incoming water valve at the heater. Also turn off the water heater power and gas. Open a hot water faucet. Water should stop flowing within a few seconds. If water doesn't stop there is cold water entering from somewhere.

 

[RS]

When I read this, I sure am glad we don't have a tankless water heater! I bet most that do spend way more on service calls than they ever save on energy!

 

[Twowaxhack]

If you have a way to valve off the circulator line, do so. Unplug the power wire first.

Then try your shower.

 

[Twowaxhack]

When I read this, I sure am glad we don't have a tankless water heater! I bet most that do spend way more on service calls than they ever save on energy!

Energy saving is not the only reason why a person would have a tankless.

If you had 2-3 teenage girls and a wife that liked to fill a jaccuzi tub, you’d go broke buying a tank/tanks trying to supply that demand.

 

[mzafar]

Turn off the incoming water valve at the heater. Also turn off the water heater power and gas. Open a hot water faucet. Water should stop flowing within a few seconds. If water doesn't stop there is cold water entering from somewhere.

Thank you! I will try this and let you know how it goes

 

[mzafar]

Turn off the incoming water valve at the heater. Also turn off the water heater power and gas. Open a hot water faucet. Water should stop flowing within a few seconds. If water doesn't stop there is cold water entering from somewhere.

I tried this just now. Turned off incoming water valve at the heater, water heater power and gas. Turned on a hot water faucet, water did not stop, continued flowing with same pressure as the cold water faucet until I turned it off. Where do I go from here... I have already changed the cartridges in all the 3 bathroom showers. Can someone please provide some guidance?
Thank you!

 

[Twowaxhack]

I tried this just now. Turned off incoming water valve at the heater, water heater power and gas. Turned on a hot water faucet, water did not stop, continued flowing with same pressure as the cold water faucet until I turned it off. Where do I go from here... I have already changed the cartridges in all the 3 bathroom showers. Can someone please provide some guidance?
Thank you!

I asked you to valve off the circulator line.

That’s most likely the problem, Check valve failed or it’s non existent, which will cause a cross connection.

Good luck

 

[mzafar]

Sorry, i forgot to mention, I did valve off the circulator line.

I also have a non-branded water softener that was installed about 5 years back. That has never been serviced since. Just added softener salt every 45 - 60 days. Could that be malfunctioning?

 

[Twowaxhack]

You have a cross connection between hot and cold water. You’ll need to find it.

 

[RS]

Sorry, i forgot to mention, I did valve off the circulator line.

I also have a non-branded water softener that was installed about 5 years back. That has never been serviced since. Just added softener salt every 45 - 60 days. Could that be malfunctioning?

Is the water coming out of it soft? We have always had softeners, they shouldn't require any service. Our last one worked fine for 25 years before we sold the house and moved, now this one has worked fine for 15!

 

[GReynolds929]

Turn off the cold stop valve at each fixture, Checking after each one until the flow stops.