Noritz N-0531S Operating and maintenance manual

NR50, NR66 and NR71 Series Heat Exchanger
Replacement
Models Include: NR50-OD
N-0531S, N-0531S-OD, NR66-SV, NR66-OD
N-0631S, N-0631S-OD, NR71-SV, NR71-OD
This instructional manual is only intended for use by a qualified service professional or authorized Noritz
Service Representative. Any unauthorized use of this manual may result in voiding the warranty.
Please contact Noritz Technical Support (866-766-7489) for additional support.
Noritz America Corporation
11160 Grace Avenue, Fountain Valley, CA 92708
Phone [phone] Fax [phone]
Page 1

NR50, NR66, and NR71 Heat Exchanger Replacement Procedure
Procedure Diagram
1. Remove front cover
(1) Disconnect electrical power to unit
(2) Turn off gas and water
(3) Remove 4 screws
(4) Remove filter and drain unit
completely
2. Remove circuit board
(1) Remove 1 screw that holds the circuit
board and let it hang outside of the
unit
3. Unplug all wires that attach to the wiring
harness and the body of the water heater
(1) Flame rod and ignition plug
(2) Freeze prevention heater, thermal
fuse (2), high limit switch
(3) Igniter plug
(4) Freeze prevention sensor
Note: The NR50 doesn’t have freeze prevention
standard, but can be added as an option.
4. Remove manifold plate
(1) Remove the 4 big silver screws on the
manifold plate that attach the
manifold to the burner
(2) Remove the 3 smaller gold screw from
the manifold plate that attach the
manifold to the gas valve
(3) Remove manifold plate
Page 2

Procedure Diagram
5. Remove fan
(1) Remove the 2 screw on both sides of
the fan, screws are located on back
side of the case
(2) When the screws are remove the back
side of the fan with drop down and fan
will rotate out
6. Disconnect water pipes coming from the
heat exchanger.
(1) Remove both “C” clamps for the inlet
and outlet pipes from the heat
exchanger
7. Remove heat exchanger from case
(1) Remove the 4 case top cover screws
(This step will be skipped with OD
Model Units)
(2) Remove the 2 set screws on the
bottom of the burner
(3) Remove the upper left and right set
screws near the top of the case (OD
Models the screws will be at the top
center of the case)
(support bottom of assembly)
8. Separate burner from heat exchanger
Remove 10 screws holding burner to
heat exchanger
OD Models
SV Models
SV Models
Page 3

9. Remove heat exchanger components from
old heat exchanger and put on new heat
exchanger
(1) Freeze prevention heater (front)
(2) Freeze prevention sensor (left side)
(3) High limit switch (right side)
(4) Thermal fuse and fasteners from 4
sides of heat exchanger, See the 4
views of the heat exchanger to make
sure the thermal fuse is routed
correctly
Procedure
Diagram
Right Side
Back Side
Left Side
Front Side
Page 4

Procedure
Diagram
10. Place new O-Rings on new heat exchanger
(1) Cold Water Pipe (smaller of 2 o-rings)
(2) Hot water Pipe
11. Replace burner gasket
(1) Remove old gasket
(2) Replace with new gasket
12. Reattach burner and heat exchanger
assembly
(1) 10 screws around perimeter of burner
13. Replace assembly back inside case
(1) Secure top left and right screws (OD
Models the screws will be at the top
center of the case)
(2) Secure bottom burner screws
14. Reconnect water connections
(1) Push the pipes in the main water
valve and flow sensor
(2) Locate 2 “C” clamps and connect to
(from left to right) main water valve
and flow sensor. The flow sensor
clamp will be smaller.
OD Models
SV Models
Page 5

Procedure Diagram
15. Replace Fan
(1) Located metal tab on top of fan and
use slot on burner to guide fan in place
(2) Tighten 2 screws on both sides of the
fan towards the back of case
16. Replace manifold plate
(1) Secure the 3 smaller gold screw from
the manifold plate that attach the
manifold to the gas valve (do not fully
tighten)
(2) Secure the 4 big silver screws on the
manifold plate that attach the
manifold to the burner (do not fully
tighten)
(3) Hand tighten all 7 screws equally.
17. Reconnect all wires that attach to the
wiring harness and the body of the water
heater
(1) Flame rod and ignition plug
(2) Freeze prevention heater, thermal
fuse (2), high limit switch
(3) Freeze prevention sensor
(4) Igniter plug
(5) Secure the wire anchor on right side of
the case
Page 6

Procedure
Diagram
18. Check for water leaks
(1) Replace water inlet filter
(2) Turn on cold water shut off valve
slowly (check for leaks around “C”
clamps)
(3) If you get leaks shut off water and re-
secure “C” Clamps.
19. Replace Circuit Board
(1) Replace circuit board on right side of
the case
(2) Secure the screw to the circuit board
20. Replace case top covers
(1) Place larger top cover first, then
gasket, then smaller cover over flue
(2) Secure top covers with 4 screws
NOTE: This step will be skipped with
OD Model Units
21. Replace Front Cover
(4) Secure front cover with 4 screws
(5) Turn on gas
(6) Return electrical power to the unit
Page 7