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WCohn
WCohn, Journeyman Plumber
Category: Plumbing
Satisfied Customers: 1133
Experience:  Journeyman Plumber/Estimator
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There, We have 2 x rennai infinity gas water heaters

Customer Question

hi there,
We have 2 x rennai infinity gas water heaters for our 3 story property. Recently we started using the lower ground shower again for the first time in 8 years. We are finding that the hot water is not consistent in the lower ground shower. IT will run hot for 3 minutes and then cold.
We have 2 showers upstairs. One never runs cold and the other one (we do not use often) runs cold after 3 minutes and then hot again after 3 minutes??
Both water heaters are working. Not sure of the problem.
Best Regards,
David
Submitted: 1 year ago.
Category: Plumbing
Expert:  WCohn replied 1 year ago.
Hi my name is ***** ***** I look forward to helping you.
Expert:  WCohn replied 1 year ago.
There could be several things going on. Are the two water heaters next to each other? If they are both working, is it at the same time? Have you had them flushed? Do you have hard water? It could be the pressure balancing spool in one of the shower valves also.
Expert:  WCohn replied 1 year ago.
Have you resolved your issue?
Customer: replied 1 year ago.
No hard water
Expert:  WCohn replied 1 year ago.
This is my wheelhouse. Much faster over the phone.
Expert:  WCohn replied 1 year ago.
Never mind the phone. Just realized you were in Australia
Expert:  WCohn replied 1 year ago.
Are these units new? Are you new to the house?
Customer: replied 1 year ago.
We have lived in the house for 8 years. The house is only 12 years old
Expert:  WCohn replied 1 year ago.
Do you have single handle shower valves? Have you done any repairs lately to your plumbing system
Customer: replied 1 year ago.
We have not done any repairs lately and have hot and cold taps (no mixers).
Expert:  WCohn replied 1 year ago.
If you are not getting error codes it is not the water heaters. Somehow cold water is getting into the hot system.
Expert:  WCohn replied 1 year ago.
Do you have a hose bibb that has hot water?
Customer: replied 1 year ago.
They are rinnai gas tankless systems. 26 litres. There is no panel to show and error code
Customer: replied 1 year ago.
what is a hose bibb?
Customer: replied 1 year ago.
I can call you on skype
Expert:  WCohn replied 1 year ago.
A fitting on the outside of the house for a garden hose
Customer: replied 1 year ago.
We have a garden hose front and back outside
Expert:  WCohn replied 1 year ago.
but no hot water to them?
Customer: replied 1 year ago.
No hot water
Expert:  WCohn replied 1 year ago.
Do you know what a cold water sandwich is?
Expert:  WCohn replied 1 year ago.
???
Customer: replied 1 year ago.
No I don't
Expert:  WCohn replied 1 year ago.
https://www.rinnai.us/documentation/downloads/Troubleshooting_Tankless_Water_Heaters.pdf Read about cold water sandwich.
Customer: replied 1 year ago.
Could it be the actual shower heads? The top shower that is inconsistent has a lower flow. The new head downstairs has a moderate flow.
The shower that does not go cold has a high pressure flow.
Expert:  WCohn replied 1 year ago.
The units could be losing the flame when high fairing but it would happen at the other shoer too. Since its only happening at the one shower you haven't used in awhile It would be the reason. Yes its called a low flow cold water sandwich!!!
Customer: replied 1 year ago.
It is actually happening at 2 showers. How can we fix it?
Expert:  WCohn replied 1 year ago.
The shower that is now being used, but wasn't before is the issue. Either the low flow shower head or the valve itself
Expert:  WCohn replied 1 year ago.
You said they aren't single handle showers?
Expert:  WCohn replied 1 year ago.
I'd take the shower heads completely off and let them run pure hot and see if it happens. If it doesn't Then I'd put on high flow heads
Expert:  WCohn replied 1 year ago.
I believe I have answered your question, I'd really appreciate a positive rating
Customer: replied 1 year ago.
They are not single handle showers. We have two showers upstairs. We use one daily and it never goes cold. The other shower upstairs we do not use often however when used, it runs cold after a few minutes. It has a low pressure flow.
The downstairs shower has not been used for 8 years and we have not placed new taps on it as we have a tenent living there. It is running cold and the pressure is moderate.
Expert:  WCohn replied 1 year ago.
Is one water heater feeding one section of the house and the other feeding the rest?
Customer: replied 1 year ago.
Sorry, downstairs shower, we have placed new taps on the plumbing as they were removed 8 years ago as we used the room for storage and not a shower
Expert:  WCohn replied 1 year ago.
Could the downstairs shower be plumbed backwards? Hot and cold crossed?
Customer: replied 1 year ago.
Not sure. What do you mean backwards?
Expert:  WCohn replied 1 year ago.
hot and cold reversed
Customer: replied 1 year ago.
Then the cold tap would have consistent hot water yes? Is only has cold
Expert:  WCohn replied 1 year ago.
No it would flow in the direction that is easiest, usually the hot side because its shorter.
Expert:  WCohn replied 1 year ago.
i proposed a Skype session
Expert:  WCohn replied 1 year ago.
Do you have a recirculation pump?
Customer: replied 1 year ago.
I don't think so?
Expert:  WCohn replied 1 year ago.
It is NOT the water heaters, unless the are shutting down and resetting. If that's the case the would beep even without a panel to give an error code.Its a cold water sandwich. The link I sent explains how to figure it out.
Expert:  WCohn replied 1 year ago.
There truly isn't anything else that it could be.
Customer: replied 1 year ago.
I will check the link
Expert:  WCohn replied 1 year ago.
Excellent. Please remember the positive rating. Its the only way I can stay on here. Its 1:17 a.m. here in the staes so I am off to bed. Thank you for using JustAnswers.com. Good luck.
Customer: replied 1 year ago.
I will give it to the plumber in Friday. Thanks
Customer: replied 1 year ago.
cheers
Expert:  WCohn replied 1 year ago.
Thank You and Cheers ***** ***** as well
Expert:  WCohn replied 1 year ago.
Please don't forget to rate me
Expert:  WCohn replied 1 year ago.
How has it worked out for you?