Monitor MWH180EX User manual

MWH180EX
Service Manual
Instantaneous Gas Water Heater
(Residential Outdoor Unit)

Table of Contents
1. General Outline of Appliance
1-1 Features .......................................................................................................................................... 1
1-2 Specifications .................................................................................................................................2
1-3 Performance ...................................................................................................................................3
1-4 General Construction (Parts Names) .............................................................................................4
1-5 Main Component Structures ...........................................................................................................5
1-6 Main Safety Devices .......................................................................................................................9
1-7 Scale Build Up Alarm....................................................................................................................10
2. Installation and Related Work
2-1 INSTALLATION INSTRUCTIONS .................................................................................................11
2-2 DIMENSIONS ...............................................................................................................................16
2-3 SUGGESTED PIPING-BASIC INSTALLATION ............................................................................17
2-4 SUGGESTED PIPING-CIRCULATION SYSTEMS .......................................................................18
2-5 VENT PIPE INSTALLATION .........................................................................................................19
2-6 GAS LINE SIZING CHARTS ........................................................................................................20
2-7 GAS PIPING .................................................................................................................................21
2-8 WATER PIPING ............................................................................................................................21
2-9 PRESSURE RELIEF VALVE ........................................................................................................22
2-10 ELECTRICAL CONNECTION ......................................................................................................22
2-11 WIRING DIAGRAM .......................................................................................................................24
2-12 DIAGNOSTIC POINTS .................................................................................................................26
2-13 SCHEMATIC DIAGRAM ...............................................................................................................27
2-14 WIRING REMOTE CONTROLLER...............................................................................................28
2-15 MAIN REMOTE CONTROLLER CMR-2250 (P/N 3748) ..............................................................29
2-16 BATH REMOTE CONTROLLER YST-2250 (P/N 3749) ................................................................30
2-17 TESTING OPERATION ................................................................................................................31
3. Service and Maintenance
3-1 Operation Principles .....................................................................................................................32
3-2 Time Charts ..................................................................................................................................33
3-3 Flow Charts ..................................................................................................................................35
3-4 Fault Findings and Error Code......................................................................................................36
3-5 Gas Setting Procedure .................................................................................................................39
3-6 Combustion Specification, Various Combination Setting ..............................................................40
3-7 Remote Controllers Special Features ...........................................................................................42
3-8 Disassembling/Assembling Parts .................................................................................................44
3-9 Procedure for Flushing Water Heater ...........................................................................................53
3-10 Exploded View .............................................................................................................................. 56
3-11 Parts List .......................................................................................................................................57

- 1 -
1. General Outline of Appliance
1-1 Features
1. High-performance & high-capacity water heater features
•Stable heating and supplying from 0.58 to 5.8 GPM with the proven temperature control
method combining the feed forward, feedback and water flow control.
• Design to reduce water temperature drops to hold temperature variation upon re-feeding
• Maximum flow rate of 5.8 GPM (22 L/min) allowing simultaneous hot water supply for
the kitchen and shower.
2. Environmentally-conscious and low NOx exhaust
•The rich-lean design of the combustion burners allows the value of NOx to be lower
than 55 ppm.
3. Self-diagnostic function
•Detects the scale-clogging of the heat exchanger assembly (warning).
•Detects the blocked exhaust system (alarm).
4. Improved reliability
•The potted PCB (Printed Circuit Board) and connectors equipped with retainers have
greatly improved the reliability of the electronic components.
5. The PCB has a function to let the LED flash upon heater trouble and the
remote controller has an error-display function.
6. With ultra-low power consumption, the optional remote controllers have
highly visible display (equipped with a backlight). The main remote controller
and the bath remote controller are different in design.

- 2 -
1-2 Specifications
Type of appliance Gas continuous flow water heater
Model number MWH-180EX
Type of
Installation
Hot water supply
Exhaust system
Outdoor only
Wall hanging
End stop system
Forced combustion
Power supply Appliance AC120V 60Hz Remote controller DC12V (digital)
Ignition system Direct electronic ignition
Outer panel material Pre-Painted Galvanized Steel Sheet
Hot water capacity
(water temp. +25°C rise) 0.58 ~ 5.8 GPM
Maximum hot water capacity
(54°F rise) 5.8 GPM
Maximum water supply pressure 150PSI (1.0MPa)
Recommended minimum water
supply pressure 15PSI (recommended 25-75 psi for maximum performance)
Minimum operational water flow 0.58GPM (2.2L/min)
Electrical comsumption
Normal 58W
Standby Main/Bath remote controller on 3.7 W
Anti-frost heater operation 84W
Connections
Gas
Water inlet
Hot water outlet
R3/4NPT
R3/4NPT
R3/4NPT
Exhaust temperature below 480°F
Noise level 49dB
NOx 55ppm Max.
Safety devices
Flame failure - Flame rod, Over heat switch 210°F, Over heat limit 203°F
Thermal fuse for heat exchanger 363°F, Over current - fuse (5A)
Automatic frost protection, Combustion fan motor rpm check - PCB
Dimensions Height 22 5/8" (575mm) Width 13 25/32" (350mm) Depth 6 1/2" (165mm)
Weight 40lbs. (18kg)
Temperrature Range Main remote controller 96 - 140°F
Bath remote controller 96 - 140°F
Available Default Temperatures
(without remote controller) 110°F, 120°F, 140°F, 165°F
(set by Dip switch on PCB)
Gas
consumption
Natural Gas
Propane Gas
Maximum 180,000Btu/h
(52.8kW)
Maximum 180,000Btu/h
(52.8kW)
Minimum (reference)
20,000Btu/h (6.0kW)
Minimum (reference)
20,000Btu/h (6.0kW)
Remote controller (option) CMR-2250 (P/N3748) Main control kitchen / laundry
YST-2250 (P/N3749) Bathroom control
Remote controller cable (option) Nonpolarized two core cable
Clearance from combustibles
Top of heater 12" (30.5cm)
Front of heater 24" (61.0cm)
Sides of heater 6" (15.2cm)
Back of heater 0" (0cm)
Floor 12" (30.5cm)
Carton box dimensions Height 30 1/8" (765mm) Width 15 15/16" (405mm) Depth 9 5/8" (245mm)

- 3 -
1-3 Performance
Performance-Capacity characteristic curves
Inlet water temperature
41°F (5°C)
50°F (10°C)
59°F (15°C)
68°F (20°C)
77°F (25°C)
6.3 GPM
6.3 GPM
5.8 GPM
0.58 GPM
0.5
96
0.58 GPM
0.5
96
0.58 GPM
5.8GPM5.8GPM
5.8GPM 5.8GPM
5.8GPM
0.5
96
0.58 GPM
0.5
96
0.58 GPM
0.5
96
0.58 GPM
0.5
96
1.0
2.0
3.0
4.0
5.0
Water flow rate [GPM]
6.0
7.0
8.0
10095 110 120
Hot water temperature [°F]
130 140 150 160 165
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
100
95 110 120 130 140 150 160
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
10095 110 120 130 140 150 160
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
10095 110 120 130 140 150 160
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
10095 110 120 130 140 150 160
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
10095 110 120 130 140 150 160
165 165
165
165
165
Water flow rate [GPM]
Hot water temperature [°F]
Water flow rate [GPM]
Hot water temperature [°F]
Water flow rate [GPM]
Hot water temperature [°F]
Water flow rate [GPM]
Hot water temperature [°F]
Water flow rate [GPM]
Hot water temperature [°F]
With water temperature 41°F (5°C) at inlet With water temperature 50°F (10°C) at inlet
With water temperature 59°F (15°C) at inlet With water temperature 68°F (20°C) at inlet
With water temperature 77°F (25°C) at inlet

- 4 -
1-4 General Construction (Parts Names)
No.
1
2
3
4
5
Description
Front Panel
Casing Assembly
Heat Exchanger
Exhaust Chamber Assembly
Gas Connection
Description
Water Filter Assembly
Drain Plug
Water Flow Sensor
Surge Protector
Water Flow Contorol Device
No.
11
12
13
14
15
No.
21
22
23
24
25
Description
Junction Box
Heat Exchanger Thermistor
Manifold Assembly
Flame Rod
Electrode
6Modulation Valve Unit
(Gas Control Assembly) Over Heat Switch (bi-metal switch)
16 26 Frost Sencing Switch
(bi-metal switch)
7
8
9
10
Combustion Fan Motor Assembly
Transformer(100V)
Water Inlet
Hot Water Outlet
Outgoing Thermistor
Igniter Transformer
Thermal Fuse Device
PCB Unit
17
18
19
20
27
28
29
30
Burner Assembly
Combustion Chamber Assembly
Fuse(3.15A)
Fuse(5A)
15
8
18
25
23
3
4
26
2
27
6
14
30
20
29
24
28
21
1
16
7
19
22
17 511 9
13
10 1210 21

- 5 -
1-5 Main Component Structures
1. Gas flow control device
•Feeds the necessary amount of gas to heat water to a set temperature, based on the
amount of water flowing in through the inlet measured by the water flow sensor and the
water temperature calculation.
•When the thermistor detects the water temperature at the inlet, the temperature is com-
pared with the setting. An electric current representing the temperature difference is
transmitted to the PCB where the current is amplified and dispatched to the Modulating
Solenoid Valve.
•An electromagnetic force caused by the current from the PCB pushes the plunger up-
ward. <Upward force>
• Pressure received at the diaphragm due to internal pressure in the chamber of the
Modulating Solenoid Valve pushes the plunger downward. <Downward force>
•The plunger stops moving and stays at a certain position when the Upward and Down-
ward force are balanced.
•As the plunger remains at the position, the valve position of the Modulating Solenoid
Valve linked to the plunger is determined. This determines a "clearance" between the
valve body and the Modulating Solenoid Valve, establishing a necessary gas quantity.
The required amount of gas is then supplied to the main burner.
•If the temperature of the heated water is lower or higher than the setting, the resistance
of the hot water temperature detecting thermistor changes accordingly to automatically
adjust the gas amount by changing greater or lower the current transmitted to the Modu-
lating Solenoid Valve. This stabilizes the heated water temperature.
•When the gas supply pressure is changed, the receiving pressure of the diaphragm
changes and also changes the clearance between the valve body and the Modulating
Solenoid Valve. The gas is controlled to remain at a constant level.

- 6 -
Diaphragm
Plunger
Plunger spring
Coil
LP 13A
2121
10
20
96.5
82
OUT 2 OUT1
127.7
UP34-33C
13A
Modulating Solenoid Valve
Solenoid Valve
Filter
IN
Pressure check hole

- 7 -
2. Water flow sensor
* Measures the water flow as its rotor (bladed wheel) spins with the passing water. The
rotation of the rotor is detected by the sensor rotor (blade equipped with a magnet) of
the wheel and the Hall element which calculates the water quantity.
3. Water flow control device
* When water flows more than water
heater capacity, hot water temperature
becomes lower than the setting. The
water flow control device automatically
reduces the water flow to prevent such
temperature drops. If the water flow is
greater than the heater capacity, a
signal from the PCB activates the water
flow control device's motor (stepping
motor). In response to this operation,
the valve body of the water flow control
device also is operated to reduce the
water flow by narrowing the water path.
Water flow fluctuations are detected and
transmitted to the PCB by the water flow
sensor. When the appropriate level of
water flow is achieved, the PCB signals
the motor to stop. Thus, the water flow
remains at this level.
ø30
ø30
50
150 °20
Main body
Rotor
Hall element IC
Sealant
Inlet
50
ø30
28.5 29.5 35
Water flow
control device motor
Valve body
Valve main body

- 8 -
4. Combustion control of rich and lean burners
1) Ignition start
After the Main Gas Solenoid Valve, Gas Solenoid Valve 1, Gas Solenoid Valve 2 open
respectively as required, the Gas Modulating Solenoid Valve, being held at the slow igni-
tion position (with gas supply at a constant rate), operates to ignite rich burners and lean
burners.
2) During combustion
When a heating capacity higher than a certain level (approximately 95,000 BTU) is re-
quired, both Gas Solenoid Valve 1 and Gas Solenoid Valve 2 are opened to burn with rich
and lean burners while the gas supply is controlled by the Gas Solenoid Valve. When the
required heating capacity becomes lower than a certain level (approximately 110,000
BTU), the Gas Solenoid Valve 2 is closed while Gas Solenoid Valve 1 remains open to
combust with 12 rich burners, with the gas supply controlled by the Gas Modulating Sole-
noid Valve.
Gas
Gas Solenoid Valve 2
Gas Solenoid Valve 1
Combustion fan
Electrode Flame rod
Main burner
Gas Modulating
Solenoid Valve
Main Gas
Solenoid Valve