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I have Rinnai RUCS75 tankless water heater and I need to…

I have Rinnai RUCS75...

I have Rinnai RUCS75 tankless water heater and I need to know the dip switch settings to get the maximum heat output because I cannot run a bath or shower or any 2 faucets at the same time and get hot water out. This has been extremely stressful. I need hot water for my family. Please help.

Contractor's Assistant: Did you double-check the thermostat's settings? And what about the filters?

There is no thermostat control.

Contractor's Assistant: Do you plan on doing the work yourself?

I've already installed it and just need to know which switches to turn on. So yes.

Contractor's Assistant: Anything else we should know to help you best?

Just the switch settings to get the maximum efficiency please.

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Answered in 1 hour by:
3/10/2018
Mike R.
Mike R., Plumber
Category: Plumbing
Satisfied Customers: 2,948
Experience: 20 years of plumbing experience, including high end homes and service work.
Verified

Hi, I'm Mike and I have 20+ years of experience in the home improvement field. I'll be glad to assist you today.

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Is this a new installation or existing? Have you already referred to the manual for the dip switch settings and adjusted them?

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Are you getting consistent hot water just not hot enough or is it intermittently hot and warm?

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Customer reply replied 1 month ago
It's a new install. The temperature is only consistent with small faucets with a limited volume flow and it is only warm. When I run the bath or shower it's cold and it's obvious that it's not hot enough to keep up with the volume.
Customer reply replied 1 month ago
I've been searching and have found that a lot of people have this same issue with tankless heaters. The factory settings are set at a low temperature for safety reasons. I have found the answer to my problem with other brands and models but not mine.
Customer reply replied 1 month ago
When I get warm water out of a faucet I have only the hot valve on 100% and it's still nowhere near ideal.

The temperature is consistent though? The dip switch settings are in the manual. Do you have it? The water flow is much lower for hot water than cold water?

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Customer reply replied 1 month ago
I recently installed a new kitchen sink faucet with a color changing LED sprayer that ranges from blue to green to red based on the temperature of the water. It has flickered into the red a few times for only a brief second. This should give you an idea that the water is not hot by any factory standard.

The water should still be pretty warm even on the factory setting. There may be other issues that are causing this. Do you have the manual to refer to the dip switch settings? Did you install the water heater yourself? When opening a sink faucet, is the hot water flow much lower than the cold?

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Customer reply replied 1 month ago
I have the manual but it isn't helpful at all. It only talks about flipping 1 of the switches if it's in a high altitude location. No, the flow/ pressure is the same as the cold valve.
Customer reply replied 1 month ago
It's only warm when only the hot valve is open. Does not get hot.

Do you have the manual with you? Will you look at page 54 and see if it has temperature dip switch settings there? I have a manual here but just want to confirm it is the correct one.

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I do have the picture. Do you have the manual and are the temperature dip switch settings on page 54 of that manual?

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That is just the quick reference guide. Do you not have the full manual?

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Customer reply replied 1 month ago
I'm looking for it. I think my fiance must have put it away somewhere.

I see. Do you also have the optional temperature controller or no? Or is there a display on the unit? Some have the display and some do not and the controller is optional.

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Customer reply replied 1 month ago
No controller. Just a 2 digit digital display.

What is the current maximum temperature setting on the display?

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Customer reply replied 1 month ago
It does not tell temperature. There are no buttons. When I turn the water on it only displays " 1 "

Oh, alright. There are a few different models of Rinnai water heaters. It is hard to wrap my head around which one it is sometimes. So, in the manual (when you find it) the switches on SW1 should be SW5 on SW6 on to set it to 140 degrees but certainly confirm in the manual. That should be on page 54 of the manual. Right now it looks like it is set for 120 degrees but even at 120 it should get better than warm. Was this water heater a replacement for a tank water heater?

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What size and type is the gas line on the water heater? Is it natural gas or propane?

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Customer reply replied 1 month ago
it replaced a tank heater. Natural gas. I used a 3/4" gas line because I know 1/2" isn't enough.

Flex line or black iron? Is the gas pipe coming directly from the meter and how long is the line?

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Very good. So it was just the settings. I wanted to be sure that it was not something else like fuel etc. Technically the gas line is still too small but it does not mean that it will not work just fine. The inner diameter of 3/4 flex line is smaller than black iron. If you do start to have issues with error codes relating to failed firing that would be where to start but chances are it will be totally fine and not cause an issue at all.

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Customer reply replied 1 month ago
I'm so happy! My fiance is too! Now she can take a hot bath. We are so grateful. Thank you thank you thank you!

You are very welcome. If anything else comes up I am happy to continue to help even after positively rating my service. Happy hot watering!

Mike R.
Mike R., Plumber
Category: Plumbing
Satisfied Customers: 2,948
Experience: 20 years of plumbing experience, including high end homes and service work.
Verified
Mike R. and 87 other Plumbing Specialists are ready to help you
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Customer reply replied 1 month ago
I just noticed that the iron pipe gas line is only 1/2"
Should I redo all fittings back to where I can do 3/4" or is 1/2 plenty?

The iron pipe size is actually has the same inner diameter as the 3/4" flex. It should be fine but if you do have problems in the future you know where to start. You may actually have an oversized meter and excellent gas pressure that will keep it running fine.

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