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Gaztech, HVAC Technician
Category: HVAC
Satisfied Customers: 455
Experience:  Owner at Gaztech
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I have a Rinnai R94LSi that's been installed and working

Customer Question

I have a Rinnai R94LSi that's been installed and working great for several years. A couple months ago we started getting water that was about 30 degrees colder than the temp set on the Rinnai. Flushed the system and cleaned the flame rod which didn't help. Finally cleaning the outgoing water thermistor did the trick, as it wasn't reporting the correct temps.
Now, it's doing the same thing (water 20-30 degrees colder than normal), but this time the thermistor seems to be acting correctly based on testing the resistance against values in the manual. What should I try next? Both times this has happened, there has been no error code given by the unit. It acts like everything is great, and it advertises that the outgoing water is the correct temperature (as checked with the down arrow-off/on button trick).
Any ideas of what to try next?
Submitted: 1 year ago.
Category: HVAC
Expert:  Gaztech replied 1 year ago.
Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue.If my initial response doesn’t answer your question then let me know and we can continue our conversation.NOTE: I can only get paid for assisting you if you click FINISHED and RATE ANSWER after you are satisfied with answer.Are you ready?
Customer: replied 1 year ago.
Expert:  Gaztech replied 1 year ago.
I had that issue with a Rinnai last month and resolved the issue after replacing the main control, it did not read the correct resistance of the thermistor, I confirm that with a different sensor with .45 k oms differential
Customer: replied 1 year ago.
is the thermistor the only thing controlling the outgoing temp, or is flow control related? I ask because I noticed last night that the reported flow control numbers don't appear to be accurate either.
Expert:  Gaztech replied 1 year ago.
the flow switch does not control the temp. it will shut off system
Expert:  Gaztech replied 1 year ago.
Customer: replied 1 year ago.
Can you be more specific about how to confirm I need a new PCB? I need a new thermistor first? I'm not sure what differential I would be measuring, since I would assume the new thermistor would have the same resistance levels as the current one.
Expert:  Gaztech replied 1 year ago.
If the resistant of thermistor is to spec,as you said there is no need to replace it, the pcb is not reading as it should.
Customer: replied 1 year ago.
When you said, "I confirm that with a different sensor with .45 k oms differential" what did that relate to? That you tried a different sensor and the pcb read it differently when it should have read it the same as the first one? Is there any other test I should do to confirm that replacing the pcb is the only fix?
Expert:  Gaztech replied 1 year ago.
That is what I am saying, other than that there Might be several volt tests that could be done with a good service manual.I will let another expert share their knoledge
Expert:  HVAC Guru replied 1 year ago.
Hello and thanks for using this service, if you have been waiting do not worry or get upset. I am HVAC Guru an extremely experienced tech on the site and I try to get to as many customers as I can. I just picked up your question now. NOTE it takes time for me to type research and add links so please wait for me to respond back I can only do this so fast. Secondly I am not paid anything until you rate my service good using the STAR RATING LINK at the top of your page, the money is paid to the site not me directly. Answer: Replace the PCB based on what you have done nothing else will cause that. All I ask is please use the Star Rating Link at the top of your page before leaving, that is the only way I am paid anything through the are greatly appreciated so thank you very much for using this service. If you have any other questions just post back to me here anytime!
Expert:  Gaztech replied 1 year ago.
I am sorry but there is nothing different in your answer than what I previously explained to customer, Same answer.

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