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Rick, Construction Supervisor
Category: Plumbing
Satisfied Customers: 21755
Experience:  Licensed Master plumber with 40+ yrs. experience.
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Rinnai Tankless Water Heater has no hot water

Resolved Question:

I have a Rinnai Tankless Water Heater. It froze here last night and I had no hot water this morning. I ran a diagnostic on the Rinnai remote inside my house to reveal that the water temp in my exterior unit was 60 degrees. So I examined the ingoing and outgoing pipes connected to the unit - there is some missing insulation on these pipes leading me to believe that one or both is frozen. Am I on the right track? If so, what will I need to do unfreeze these pipes? Can I do it myself? Thanks for any input you might have.

Submitted: 6 years ago.
Category: Plumbing
Expert:  Rick replied 6 years ago.

Welcome to JustAnswer, I will do my best to help you solve your problem
Is there no water coming out of the hot water faucet or is there water but it's just not hot?

JACUSTOMER-0spvukfq- :
Water runs out of all taps in the house at cold temps, but when you attempt to adjust toward warm or hot temps, water stops.

Rick the plumber :
You only have single handle faucets?
In the sinks as well as the shower

JACUSTOMER-0spvukfq- :
Dual in the bathroom sinks. Single on kitchen sink. Single in both showers.

Rick the plumber :
So when you turn on just the hot side in the sinks nothing comes out?

JACUSTOMER-0spvukfq- :

Rick the plumber :
Sounds like frozen pipes
You could try thawing the pipes with a hair dryer on high as long as the area where the pipes were exposed to freezing temps is now above freezing

JACUSTOMER-0spvukfq- :
Called Rinnai Tankless customer service and they think it is the exterior pipes that lead to and from the rinnai unit.

Rick the plumber :
Sounds probable to me

JACUSTOMER-0spvukfq- :
I'm in Charleston, SC. I think we are creeping toward 32 but not there until the afternoon.
Should I be worried about cracked pipes.

Rick the plumber :
Hard to say, if you plan on leaving the house turn the water off at the main shut off
In the mean time leave a hot water faucet open - one that will be noticed if the water starts to flow on its own
You could try the hair dryer but if air temps are below freezing where the pipes are thawing will be difficult

JACUSTOMER-0spvukfq- :
I'm not leaving. If I go the hairdryer route, I should leave the water on, correct?? Also, is the main shut off down at the street?

Rick the plumber :
The main shut off inside the house, yes leave the water on while you are there

JACUSTOMER-0spvukfq- :
Okay. Will insulating those pipes prevent this in the future? Can I do that myself or is it advisable to get a professional to examine the situation? Of course, I'd prefer the to do it myself, but I def want to resolve the issue. I checked the neighbors house, and we are only missing about a foot of insulation. Is that enough to cause this?

Rick the plumber :
Yes any missing insulation could cause this if the weather conditions are right. You might want to call in a pro since they will be able to resolve this quickly. There is some risk of damaging your Rinnai if the temp readings are inaccurate

JACUSTOMER-0spvukfq- :
Do you mean the hairdryer route could damage the Rinnai? I didn't think you meant that, but want to be sure.

Rick the plumber :
No I meant if the Rinnai drops below freezing it could be damaged

JACUSTOMER-0spvukfq- :
Okay I see. Well thanks for the advice. Is that all that needs to be done?

Rick the plumber :
That's the standard procedure. You leave a faucet open to take the pressure off the line and it will also let you know when the pipe thaws.

JACUSTOMER-0spvukfq- :
Okay. Great and thanks for your help.

Rick the plumber :
Thanks for using JustAnswer

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