Rinnai Continuum Series User manual

RINNAI
Continuum
Water Heater Model
REU-2424-W and REU-2424-C
General Use
Rinnai Corporation
103 International Drive
Peachtree City, Ga. 30269
Telephone number [phone]

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No portion or part of this manual may be copied without prior permission from Rinnai Corporation.
Key to Warning Symbols
Please follow instructions in chapters to ensure safe and appropriate service.
After completing the service and confirming that there are no water or gas leaks or incorrect wiring, test
operation of the appliance. After confirming normal operation, explain what was serviced to the customer
and the operating principles, if necessary.
The information in this manual was compiled by Rinnai Technical Services. While many individuals have
contributed to this publication, it will be successful only if you – the reader and customer – find it useful.
We would like to extend an invitation to users of this manual to make contact with us, as your feedback and
suggestions are valuable resources for us to include as improvements. Rinnai is constantly working toward
supplying improved appliances as well as information, and specifications may be subject to alteration at
any time.
Failure to comply with the following instructions may results in serious personal injury or
damage to the appliance.
Be careful of possible electric shock. Wiring inside this appliance may potentially be at 120 volts.
Disconnect power supply to unit when carrying out the following service repairs.
Read Fault Diagnosis and Wiring Diagram carefully to avoid incorrect wiring.
Do not disassembly. Parts within can not be exchanged or diagnosed faulty.

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Table of Contents
Glossary of Terms and Symbols …………………………………………………………………….. 3
1. Introduction ………………………………………………………………………………….. 4
2. Features ………………………………………………………………………………….. 5
3. Dimensions …………………………………………………………………………………. 7
4. Installation ………………………………………………………………………………… 8
5. Remote Controls ……………………………………………………………………………. 9
6. Safety Devices ……………………………………………………………………………….. 10
7. Specification ………………………………………………………………………………… 13
8. Cut-away Diagram ………………………………………………………………………….. 14
9. Schematic Diagram ………………………………………………………………………… 15
10. Combustion Specifications …………………………………………………………………. 16
11. Water Flows …………………………………………………………………………………. 17
12. Main Components……………………………………………………………………………. 19
13. Time Charts ………………………………………………………………………………….. 21
14. Operation Flow Principle …………………………………………………………………… 22
15. Operation Principles ………………………………………………………………………… 24
16. Error Messages ……………………………………………………………………………… 26
17. Diagnostic Points ……………………………………………………………………………. 27
18. Wiring Diagram …………………………………………………………………………….. 28
19. Fault Diagnosis ……………………………………………………………………………… 30
20. Electrical Component Analysis ……………………………………………………………. 39
21. Gas Pressure Setting Procedure …………………………………………………………… 44
22. Dismantling for Service ……………………………………………………………………. 46
23. Exploded Diagram ………………………………………………………………………….. 52
24. Parts List …………………………………………………………………………………….. 56

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Glossary of Terms and Symbols
This glossary of terms and symbols is provided to assist you in understanding some of the language
used throughout this manual.
DB(A) - sound pressure level in decibels, “A” range
DC - direct current
AC - alternating current
WFCD - water flow control device
FB - feedback information
Hz. - hertz
IC - integrated circuit
BTU/H - British thermal units
PSI - Pounds per square inch
LED - light emitting diode
GPM - gallons per minute
mA - milliamps
W.C. - inches of water column
mm - millimeters
Nox - oxides of nitrogen NO & NO2
OHS - overheat switch
PCB - printed circuit board
CPU - central processing unit
POT - potentiometer
rpm - revolutions per minute
SV - solenoid valve
∅- diameter
∆°F - delta T or temperature rise above ambient
POV - modulating valve
TE - thermal efficiency
TH - thermistor
TIN - temperature of incoming water
Tout - temperature of outgoing water

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1. Introduction
The brand name Continuum refers to “Endless Hot Water”. The new Continuum series has been developed
in response to the growing changes in the lifestyle of our customers, and the increasing diversification and
sophistication of demand in the marketplace.
The Continuum series offers reduced cost with advanced safety features, and an option to connect one,
two, or three remote temperature control pads.
The Continuum model REU2424-W is delivered with the maximum hot water temperature output set at
120 °F without the remote control. The REU2424-C is delivered set at 140°F without the remote control.
When using controllers you can adjust your hot water output from 96 – 120 °F using the “BC” and “BSC”
controllers. The “MC” control will allow water temperature adjustments from 96 – 140 °F and the “MCC”
control used with the commercial unit allows adjustments from 96 - 180°F. .
About the Continuum
The front cover of each appliance in the new series is formed from 0.6 mm coated steel. Secured to the
main box assembly by (4) screws. Seals around the front cover and the flue outlet prevent water from
entering the appliance.
Air inlets are situated in the front panel of the 2424 external unit. Air passes through the inlets and is drawn
into the combustion chamber at the rear of the fan housing. The by-products of combustion on the external
unit are expelled from the appliance through a flue outlet situated on the front of the appliance, at the top.
The general layout of components can be seen in the cut-away diagram, see table of contents for page
number. All components are supported within the unit’s casing, which is made from 0.8 mm coated steel.
The heat exchanger occupies the top section of the casing, and the burner is situated in a chamber formed
from 0.8 mm aluminized steel, attached to the bottom of the heat exchanger. The copper tubing material
used in the heat exchanger consist of, Phosphorus Dioxide Copper, (C1220P). The material used to solder
the heat exchanger pipes is, Phosphorus Bronze Brazing, (main components are P, Ag, and Cu) (JIS No.
BcuP-2). None of these materials contain lead.
The air for combustion is supplied by a fan, which is connected to the burner box by a duct at the left side
of the appliance, directly under the burner.
Gas and water controls are situated at the bottom right of the appliance, directly under the manifold. The
“O”ring material on the water and gas connections are made from EPDM, (Ethylene Propylene Diene)
rubber.
The burner assembly is made up of (18) identical stainless steel Bunsen burners, secured by an aluminized
steel framework. Each burner is capable of handling up to 10,000 BTU’s. An aluminum manifold with
(18) integrally molded injectors supplies gas to the burners, and is attached to the front lower cover of the
burner box.

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2. Features
Installation
The lightweight, slim, compact design enables ease of installation, and improved appearance. The remote
controls (where fitted) are connected to the appliance by (2) core non-polar cable, ensuring easy wiring and
eliminating problems of mis-connections. Since the remotes use a 12 VDC digital signal, there’s no-way
you can cross up the wiring. You can connect the black wires at one terminal, black and white at another,
and still not short the units out.
Low Noise Level
Low noise level design enables these appliances to be installed in apartment units, townhouses, and other
high density residential areas with little concern about noise disturbances.
Safety
Varies safety devices controlled by a micro- computer ensure complete safety. Also, the anti-frost device
(where fitted), automatically prevents the water inside the appliance from freezing by using small electrical
ceramic heaters, connected to the pipe-work at strategic locations throughout the appliance. The unit has a
secondary freeze prevent device that will allow the unit to fire for three seconds, if the water temperature
inside the appliance drops below 37 °F. This mode will heat the water inside the unit back up to 57 °F.
The anti-frost devices should prevent the unit from freeze-ups down the –30 °F, in a no wind situation.
This feature functions as long as the unit has power. See optional freeze protection in the owner’s manual
for power failure protection.
Economy
Direct ignition to the main burner eliminates wasteful pilot gas consumption. The combustion fan rpm is
proportionally controlled with the gas consumption. This maintains high energy efficiency, as the gas
consumption changes with increased or decreased water flows. The unit’s AFUE rating is 82%.
Water Supply Control
The water supply capacity varies proportionally from 0.6 to 6.5 GPM’s. A suitable volume of hot water
can be supplied throughout all seasons by the water flow control device and water flow servomechanism.
The Continuum 2424 and 2402 models will supply up to 6.5 GPM’s, controlled by an automatic electro-
mechanical water control flow device. Details pertaining to water flows can be found in the water flow
charts in this manual.

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Water Temperature Control
With an “MC” remote control connected, the hot water control range at the key pad is 96 – 140 °F. The
“BC” and “BSC” key pads allow for adjustments between 96 – 120 °F. The “MCC” key pad allows the
commercial unit to be adjusted from 140 – 180 °F. The “MCC” key pad can be configured to deliver water
temperatures from 96 - 140°F in low temperature applications. Contact Rinnai for details when using the
commercial unit in temperature applications below 140°F . This allows the Continuum to be set to comply
with various State codes pertaining to temperature control in homes, child care centers, and elderly care
centers were the temperature can not excess a certain set point.
Over Temperature Control
All Continuum models incorporate a device to prevent the hot water temperature from exceeding the pre-
set temperature by more than 4 °F.
Temperature Locks
With the remote control(s) connected, the pre-set water temperature can only be altered between 96 – 110
°F while water is flowing. Also, if the remote control circuit fails while water is flowing, the unit defaults
back to 100 °F. This prevents inadvertently increasing the temperature to a hazardous level, while someone
is in the shower. This is an Anti-Scald feature.

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3. Dimensions
Note: All dimensions are in inches.

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4. Installation
Recommended piping. .

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5. Remote Controls
The MC45-3US, BC45-3US, BSC45-3US , and the MCC45-3US remote key pads were specifically
designed for use with the Continuum water heaters.
Features include:
•Color coordination to allow immediate recognition of the temperature “hot” and “cold” buttons.
•Large LED display.
•Temperature adjustments in two degree increments from 96 – 116 °F, then one four degree increment from 116 –
120 °F on the BC,BSC and MC controllers. The “MC” controller has two additional ten degree increments, from
120 to 130, and 130 to 140 °F. The BC, BSC and MC controls are for domestic use. The MCC control allows
the temperature to be adjusted from 96°F - 180°F , this control is used only on the REU-2424C commercial unit.
•Water temperature adjustment only in the range of 96 – 110 °F while hot water is flowing.
•Anti-Scald feature defaults unit back to 100 °F, if remote fails or becomes disconnected while water is flowing..
•Enhanced communication system between the remote controls, allowing priority temperature selection at each
remote control.
•The remote offers self-diagnostics in the event of a fault with the unit, simplifying service calls.
•Flashes “LC” in the event of a liming condition. To reset the “LC” mode, power must be turned off to the unit
and then reapplied.

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Suggested Connection Methods for Remotes
There must be at least one cable from the remote control(s) connected to the Continuum water heater.
Power for the remote(s) is supplied from the PC board. On the front of the PCB, there are two screws
labeled terminal, this is the 12VDC digital power supply for the remotes.

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6.SafetyDevices
Flame Failure
Situated to the right of the burner in the front of the combustion chamber, the flame rod monitors the
combustion process. This sensor monitors the flame intensity, while the PCB compares this signal to the
feed back signal from the combustion fan motor, water flow control, and gas flow through the POV valve.
If any one of these feedback signals are incorrect, the unit will shut off, preventing discharge of gas to the
burner.
Over Heat Protection Device
Also referred to as an Over Heat Switch. This device is fitted to a bend section at the inlet to the heat
exchanger. If the flame remains on to the burner after the tap is closed, and the water temperature inside
the heat exchanger reaches 194 °F a 12 volt DC bi-metal cut-off switch, will shut off the gas supply to the
solenoids.
No Water
Should the incoming water flow become restricted or stop, the water flow sensor will cease to send a
magnetic pulse signal to the PCB, in turn preventing gas to flow into the combustion chamber. If you have
restricted flow, first check to ensure the inline water filter is not clogged up.
Thermal Fuse
Wrapped around the entire surface of the heat exchanger you will find a thermal fuse. This device activates
in the event the heat exchanger burns out, or the temperature outside the heat exchanger reaches 279 °F. If
the thermal fuse melts, it breaks an electronic circuit which in turn shuts off the power supply to the gas
solenoids, shutting the unit off.
Combustion Fan Revolution Check
The combustion fan rpm’s are continually monitored by a magnetic pulse generator connected to the PCB.
If the fan revolutions deviate from the speed required for complete combustion, a signal is sent to the PCB
and the revolutions adjust accordingly. (If not the unit shuts down)
Automatic Frost Protection
When the temperature inside the appliance drops below 37 °F , the frost sensing device inside the
appliance activates the anti-frost heaters, to prevent the water inside the unit from freezing. The anti-frost
heaters remain ON until the temperature inside the appliance rises to 57 °F. There are four (16) watt anti-
frost heaters located at various points throughout the main water flow area of the appliance. The unit also
incorporates the ability to fire for (3) seconds in the event the anti-frost heaters can not keep the water
temperature from dropping below 37 °F. This unique feature will heat the water in the lines inside the
appliance back up to 57 °F. Both of the above features function as long as the unit has power. There is

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an optional freeze protection system that can be added to the unit’s piping, that will dump water out of the
unit in the event of a power failure. See owner’s manual for details on this system.
5 °F Over temperature Cut-Off
The temperature of the outgoing hot water is constantly monitored by the water temperature thermistor
located near the outlet of the appliance. If the outgoing water temperature reaches 5 °F above the preset
temperature, the burner will automatically go out. The burner will only ignite again once the outgoing hot
water temperature falls below the preset temperature.

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7. Specification
Type of appliance Temperature controlled continuous flow gas hot water system
Operation With or without remote controls, mounted in Kitchen, bathroom, or laundry room
Exhaust system Forced combustion
Rinnai model No. REU-2424-W REU-2424-WC
Minimum gas rate 19,000 BTU’s
Maximum gas rate 180,000 BTU’s
Hot water capacity 0.6 – 6.5 gals./min. unmixed @ 50°F rise 2.95 gals./min. unmixed @ 100°F rise
Default temperature
(without remote) Set using
switches on PCB
108, 120, 130, 140, 150, 160, 170, or 180°F
Temperature range
(with remotes connected) 96 – 120 °F with the BC and BSC control(s)
96 – 140 °F with the MC control,
96°F - 180°F with the MCC control (2424C model only)
Factory default temperature REU-2424-W set at 120°F REU-2424-WC set at 140°F
Approved gas types Propane: Natural:
Installation External
Dimensions Height 13 ¾” Width 23 ¾”
Depth 6 ¾”
Weight 44 Lbs.
Efficiency rating 82 %
Noise level 49 dB (A)
Connections Gas supply ¾” MNPT Cold water inlet ¾” MNPT
Hot water outlet ¾” MNPT
Ignition system Direct electronic ignition
Electrical consumption Normal 55 watts Standby 8 watts
Anti-frost protection 80 watts
Water temperature control Simulation feedforward and feedback
Water flow control Water flow sensor and automatic electro-mechanical water flow control device
N
ormal operating pressures
(water) 20 – 174 PSI
Power supply Appliance 120 VAC, 60 Hz.
Remote control(s) 12 VDC digital
Safety devices
Flame failure – Flame rod
Boiling protection 203 °F lockout thermistor (25 seconds)
Remaining flame (OHS) 194 °F bi-metal switch
Thermal fuse 279 °F
Automatic frost protection – Bi-metal sensor & anti-frost heaters
Combustion fan rpm check – Integrated circuit
Over current – two 3 amp glass fuses
Remote control(s) MC-45-3US BC-45-3US
BSC-45-3US
MCC-45-3US
Remote cable Non polarized two-core cable

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8. Cut–awayDiagram
REU2424

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9. SchematicDiagram

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10. Combustion Specifications
Gas type Firing rate Measurement REU-2424-W/WC
Input Natural Low fire
High fire BTU/H BTU/H 19,000 180,000
Input Propane Low fire
High fire BTU/H BTU/H 19,000 180,000
Gas consumption Natural
Propane Low fire High fire KW 5.93 52,3
Integral Injector size Natural
Propane MM
Ø1.7 mm (0.067”)
Ø 1.0 mm (0.039”)
Manifold Gas Pressure Natural
Low fire High fire W.C. 0.43” 5.3”
Manifold
Gas Pressure Propane Low fire High fire W.C. 0.59” 8.7”
Damper Natural
Propane NIL A
Burner type Nat./L.P. Bunsen burner
Dip switches Contact Rinnai before setting or changing any switches
Contact Rinnai for dip switch settings when changing PC board or setting up unit for special
applications. Failure to set dip switches to the proper position, will result in damage to the unit,
property damage, personal injury or death. DO NOT adjust dip switches unless you have written
permission from Rinnai. Call 1(800)621-9419 to set-up a special training class pertaining to dip
switch functions. Maximum Capacity
Modulating Valve
(mA) Natural Propane mA 147 229 147 229
Combustion Fan
(Hz.) Natural Propane Hz. 264 272 264 272
Minimum Capacity
Modulating Valve
(mA) Natural Propane mA 20 20 20 20
Combustion Fan
(Hz.) Natural Propane Hz. 96 87 96 87
Slow Ignition
Modulating Valve
(mA) Natural Propane mA 91 152 91 152
Combustion Fan
(Hz.) Natural Propane Hz. 160 160 160 160

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12. Water Flows
A simple calculation of the water flow rate, in gallons per minute, can be made using the chart on the next
page, or simply using formula provided below. The chart on the following page indicates the water flow
from the Continuum at various temperature rises up to a 140 degree rise.
a. How to read the charts:
The vertical plane indicates water flow in gallons per minute, and the horizontal plane indicates the
temperature rise. The chart shows flow rates up to a 140 degree rise. Therefore, the water flow chart can be
used to help you size your applications, if you know the temperature rise needed. The temperature rise is
the difference between the temperature of the incoming water and the selected temperature at the remote
control(s). Another name used in place of temperature rise, is delta T.
Select the appropriate temperature rise. Draw a vertical line up the graph from the selected temperature rise
until it intersects the curve. The point at where these lines intersect indicates flow at that temperature rise.
b. How to calculate water flows:
The following information is an outline of the formula required to measure accurately the flow rate in
gallons per minute, as well as being the base for the chart on the next page. The most useful way in which
this formula can be utilized, is to calculate the water flow rate where there is maximum gas input of
180,000 BTU’s.
EXAMPLE:
BTU’s ÷∆T x 500 = GPM’s
GPM’s = (180,000 BTU’s x .82 efficiency rating) ÷∆Tx 500
GPM’s = 147,600 ÷(Requested water temperature – incoming water temperature) x 500
GPM’s = 147,600 ÷(120 °F requested – 65 °F incoming) x 500
GPM’s = 147,600 ÷(55 °F delta T x 500)
GPM’s = 147,600 ÷27,500
GPM’s = 5.367

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Unmixed Water Flows for REU-2424
The chart below can be used to determine water flow rates in “gallons per minute” at a given temperature
rise. In order to figure flow rates, you need the following information; requested water temperature and
inlet water temperature Next, subtract the inlet water temperature from the requested temperature to get
your delta T or temperature rise. Then, locate your temperature rise at the bottom of the chart. Follow that
line vertically until it intersects with the flow rate line to the right. This indicates the flow rate at your
temperature rise.

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12. Main Components
1. Mechanical Water Regulator
Rinnai’s unique water regulator mechanism ensures the hot water is maintained with no noticeable change
to the desired temperature during use, even if water pressure drops due to another tap being turned on and
increasing the demand.
The following graph shows that maximum flow is approximately 6.5 gallons per minute for the
Continuum. This maximum flow is reached at 29 PSI inlet pressure respectively.
2. Preset Bypass
A preset volume of cold water is mixed with water heated in the heat exchanger.
3. Burner
The burner assembly is made up of 18 identical stainless steel
Bunsen burners, secured by an aluminized steel framework.
An aluminum manifold with 18 integral injectors supplies gas
to the burners, and is attached to the front lower cover of the
burner box and Change Over Solenoid.
4. Changeover Solenoid Valve
The changeover solenoid increases the flexibility of the regulator/modulating valve by supplying gas to the
right hand size of the burner only, (up to 40% of the total BTU load) or both sides of the burner from 40 to
100% of the total BTU load, through the tandem manifold.