Question about Noritz 7.1 Gpm Natural Ng Gas Tankless Hot Water Heater

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Noritz not staying hot

My Noritz (751M) will not keep water hot. Watching the burners and it cycles from 1 to 3 and back again every few seconds. Sometimes water is hot and all seems to work fine..

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How many faucets do you have on when this happens? Turn on more than 1 and if it still does the samt thing than I would check to see if the inlet water screen has debris in it. Valve off the unit and look at the inlet water side and theres a screeen that you should be able to remove and clean undeneith some running water and then replace. Good Luck

Posted on Jan 07, 2009

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I have a Noritz model# N/084m/DV Serial# 200412-000328 and the water does not stay consistently hot it fluctuates in temperature very annoying please advise


hi there

if the unit is a few years old it or if you have hard water it may be the heat exchanger or the domstic hot water sensor.

hope this helps

Dec 22, 2010 | Noritz Water Heaters

1 Answer

I have a nortiz 063-s tankless, and it won't stay on...I'm thinking it's the computer, please help


There are several things I would look for:
-Flashing burner light (indicates an error code)
-Trying flowing more hot water. In the summer alot of times you'll flow less hot water because your cold water is warmer. If you flow additional hot water at your shower, it will ensure the unit stays firing
-If the unit doesn't fire at all, you may have debris in your cold water filter or a stuck flow sensor. Call tech support to help you with cleaning a flow sensor.

May 29, 2010 | Noritz 6.3 Gallon Residential Tankless...

1 Answer

Noritz f 76 error blinking f 76 and on off light blinking at the same time. Everything works fine turned on and off hot h20 it goes to burner on 120 and then goes back to blinking f 76 after burner...


F76 is a communication error between two quick connected heaters. To clear the code, disconnect power from both heaters, wait 20 seconds, then reconnect power.

Apr 23, 2010 | Noritz 6.9 Gallon Residential Tankless...

2 Answers

After water to house was shut off, my Noritz tankless water heater is on but won't produce hot water. On the unit, the light indicating that the burner is on stays off now.


you probably had debris get into the filter or flow sensor when the water was turned back on. I'd recommend checking the filter first and if that doesn't work, call Noritz Tech support to help you with the flow sensor.

the filter is a black plug located on the cold water line (labeled cold on the bottom of the unit). It points torwards the left.

Apr 14, 2010 | Noritz 7.1 Gpm Natural Ng Gas Tankless Hot...

1 Answer

Sometimes the hot water just goes cold


Here are a couple things to look for:

1) flashing burner light - a flashing burner light indicates the unit is getting an error code
common error codes:
A. continuous flashing - ignition failure or abnormal combustion; look for visible water in the machine indicating a leak, check gas pressure, debris or buildup on flame rod/igniter plug, or clean unit with compressed air
B. 3 flashes - error 16, abnormal outlet water temperature; typically this code indicates you'll need to descale you unit
C. 4 or 5 flashes - exotic error codes; you should contact Noritz technical support to deal with these codes

2. If there is no flashing code, try increasing the hot water flow. In the summer time you typically use less hot water; this can result in intermittent operation of your tankless heater. Increase water flow by either: A. cleaning your showerhead and removing scale deposits B. widening your flow restrictor C. Remove your flow restrictor in the showerhead

3.If none of these resolves your problem, you probably have debris in your flow sensor. Contact Noritz technical support for a walkthrough on removing debris from a flow sensor.

Feb 18, 2010 | Noritz 6.3 Gallon Residential Tankless...

2 Answers

We have a customer that has a 751od who says at times thier water gets cold for a few seconds. No error codes on the remote. They claim it does it at different fixtures. Everything checks out from water...


A few things you should check:

1. Cross Connections - this occurs when cold water leaks into the hot water system through a fixture. In order to check for a cross connection: 1) turn off the cold water to the tankless 2) open up hot water fixtures in the home. The water should shut off at all hot water fixtures; if there is a continuous flow of cold water, then you have a cross connection. The most common place to find a cross connection is on old shower cartridges.

2. Ask the customer to check to see if the burner indicator is continuously lit during operation.

3. When the water goes cold at one fixture, try another near by fixture to confirm it is also cold there. If its hot at one fixture but not the other, then you have some issue with you plumbing. Tankless heaters can't pick and choose which fixtures to deliver hot water to.

4. Tankless water heaters all have a minimum flow rate that must be maintained in order to continually fire (.5 gpm for Noritz). Ensure their hot water fixtures flow at least this amount, or that the customer isn't mixing too little hot water at their fixture.

5. If they see the cold spurt during initial firing, they may be experiencing a cold water sandwich. When the heater moves from a standing state to a firing state it takes a short period to ignite and heat water. During this time it will be passing cold water through the system. Usually this cold water mixes with hot water in the line as it travels through the plumbing system, but if their fixture is very close to the heater, there won't be enough time to mix.

6. If debris has gotten into the flow sensor, this can prevent the unit from registering flow and cause intermittent firing.

Aug 27, 2009 | Noritz 7.1 Gpm Natural Ng Gas Tankless Hot...

1 Answer

Fan cycles on every few minutes.There is no demand and the burner doesn't come on but the exhaust fan cycles on for a few seconds every couple of minutes.


You're most likely getting a pressure wave (spike) that is generating momentary flow across the flow sensor. The heater is registering this "instant" flow and beginning its firing sequence. Once the flow dissipates, the unit then goes into a purge cycle. I'd recommend having your water pressure tested to make sure it isn't abnormally high (above 60 psi) or abnormally low (below 30 psi). Assuming the pressure is normal, you can use a pressure reducing valve or pressure regulator to absorb the spikes and stop the unit from cycling.

Aug 12, 2009 | Noritz Water Heaters

2 Answers

New Noritz 751M-OD not getting up to temp.


check the thermostat this would be the only thing keeping it from getting to any temp,, other then the gas valve, is it constant or happens here and there;;;

Jun 03, 2009 | Water Heaters

2 Answers

Won't Turn on.


did you check your circuit breaker for the outlet you are pluged into, is it electric or gas, for the combustion? if it is electric you might have burned up the element it has to have water on it before turning it on, if it's gas you might just have to unplug it wait 30 seconds plug it in set the temp and turn it on

May 29, 2009 | Noritz 6.3 Gallon Residential Tankless...

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