A.O. Smith T-M50 ASME User manual

T-M50 / T-M50 ASME Service manual
Ver. 1.05
1
CONFIDENTIAL
T-M50 / T-M50 ASME
On-Demand Water Heater
Service manual
T-M50
A.O. Smith Water Products Company
500 Tennessee Waltz Parkway
Ashland City, TN 37015
Toll Free: 1
-
877
-
737
-
2840

T-M50 / T-M50 ASME Service manual
Ver. 1.05
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CONFIDENTIAL
Table of Contents
1.
Specifications………………………………………...…...………….……………………...…………………………
3
2.
Exterior view……………………………………………………………………………………………………………..
4
3.
Interior view….…………………………………………………………………………………………………………..
5
4.
List of main components in the interior view……………….…………………………………………….
6
5.
Schematic diagram………………………………………………………………………..…………………………..
8
6.
Wiring diagram…………………….…………………………………………………………..……………………….
9
7.
Wiring diagram checkpoints for diagnosis……………………………………………………………….…
10
8.
Resistance values of the temperature thermistors……………..………………………………………
12
9.
Operational flow chart..……………………………………………………………………………………………..
13
10.
Component specifications………………………………………………………………………………….………
14
11.
Fault Analysis & Specifications……………………………………………………………........................
36
12.
Controls and settings………………………………………………………………………………………………….
47
13.
Components diagrams………………………………………………………………..................................
81
14.
Parts list……………………………………………………………………………………………………………………..
85
15.
Revisions…...................................…………………………...………………………………………………….
91

T-M50 / T-M50 ASME Service manual
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CONFIDENTIAL
1. Specifications
Unit Model T-M50 / T-M50 ASME
Unit dimensions H25.3"×W24.8"×D11.8"
Weight 102 lbs.
Max 380,000
INPUT
BTU/h
Min 15,000
Combustion System
Power vent
Installation Indoor, Outdoor, Direct vent
Fan motor PWM Turbo fan
Max LP 3.7”WC
Natural 2.7”WC
Combustion
Manifold
Pressure*
Min LP 0.9”WC
Natural 0.7”WC
Flow rate 0.5 to 14.5 GPM
Available set temp.
100°F to 185°F
default set 120°F
Temperature
dipswitch setting
100°F, 115°F, 120°F, 135°F, 145°F, 155°F, 165°F, 185°F
Bypass valve Yes
Water control
Thermistors 3 thermistors (In, Out, Mixing)
Available remote
controller TM-RE30
PCB Model Central board: MC50 (Part # EM306) /
Right and left computer board:T-M50 (Part # EM307)
Indicators Red LED on PCB during operation & 7-Seg LED
Operation
Power supply
control GFI (Excluding surge absorber)
Freeze protection
Ceramic heaters, Auto-FM system and Auto-firing system
Self-combustion
improvement Air Fuel Ratio detection system
Easy-link system
Yes
Future
Multi-unit system
Yes
*The manifold pressure measurement is base on conditions without front cover.

T-M50 / T-M50 ASME Service manual
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CONFIDENTIAL
5" (1 27mm)
24-7/ 8" (632 .9mm)
25-1 /4" (64 2m m)
7-3/8 " (18 6m m) GAS
1-5/ 8" (40mm) C OLD
12-1 /4 " (311 .5mm)
4-7/8" (12 2.9mm)
1/2" (11.9m m)
5-3/8" (137.3 mm) HO T
4-3/ 8" (11 0.8mm) GA S
7-5/8" (194.3 mm) C OLD
4" ( 100mm) 1 20 VAC
6-3/ 4" (171 .3mm) 12 0 VAC
1/2" (12.5 mm)
2-1/ 2" (62.1m m)
5-7/ 8" (15 0mm ) HOT
15" (381mm )
8" ( 203mm)
29-7/8 " (7 59 mm)
GAS
COLD
HOT
7-3/8 " (18 6m m)
4" ( 100mm)
4-3/8" (110.8 mm)
6-3/8" (17 1.3mm)
1-5/8" (40mm)
5-7/ 8" (15 0m m)
6-3/4 " (137.3mm)
7-5/8" (19 4.3mm)
4-7/ 8" (123.7mm)
8" ( 203.2m m)
2. Exterior view
Side view Front view
Top view Bottom view

T-M50 / T-M50 ASME Service manual
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CONFIDENTIAL
3. Interior view
1
4 4
5
5
2
2
6
7
6
7
8
8
9
10
11
12
12
13
14
15
16
16
17
18
18
19
19
2122 23
23
24 25
26
3
27
5
30
20
20
29
31
28
3
15
30

T-M50 / T-M50 ASME Service manual
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4. List of main components in the interior view
No. Description
Items# in
components
diagram
Takagi
Part #
Common parts
For other models
1 Case assembly 001 EM305
2 Burner assembly (Burners) 101 EM445
3 Igniter 102 EKN74
T-K3, T-K3-Pro, T-K3-SP/OS,
T-H2-DV/OS, T-KJr2-IN/OS,
T-K4-IN/OS, T-D2-IN/OS,
T-M32
EM302
(LP model)
4 Manifold assembly with gas
valve assembly 114
EM303
(NA model)
5 Fan motor 416 EKK25
T-K3, T-K3-Pro, T-K3-SP,
T-H2-DV/OS, T-K4-IN/OS,
T-D2-IN/OS,T-M32
6 Flame rod 103 EKK0E
T-K3, T-K3-Pro, T-K3-SP/OS,
T-H2-DV/OS, T-K4-IN/OS,
T-D2-IN/OS, T-M32
7 AFR rod 103 EKK0E
T-K3, T-K3-Pro, T-K3-SP/OS,
T-H2-DV/OS, T-K4-IN/OS,
T-D2-IN/OS, T-M32
8 Igniter rod 104 EKK0F
T-K3, T-K3-Pro, T-K3-SP/OS,
T-H2-DV/OS, T-K4-IN/OS,
T-D2-IN/OS, T-M32
9 Gas inlet 124 EM284
401 EM308
(Regular model)
10 Heat exchanger
444 EM323
(ASME model)
11 Exhaust combining box 128 EM331

T-M50 / T-M50 ASME Service manual
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CONFIDENTIAL
No. Description
Items# in
components
diagram
Takagi
Part #
Common parts
For other models
12 Water control valve 418 EKH32 T-H2-DV/OS, T-M32
13 Water inlet 434 EM295
14 Water outlet 439 EM309
15 Inlet thermistor 424 EKK38 T-K3, T-K3-Pro, T-H2-DV/OS,
T-D2-IN/OS, T-M32
16 Output thermistor 405 EKK2T T-K3, T-K3-Pro, T-H2-DV/OS,
T-D2-IN/OS, T-M32
17 Mixing thermistor 430 EKK1A T-K3, T-K3-Pro, T-D2-IN/OS
18 Hi-limit switch 403 EKN34
T-K3, T-K3-Pro, T-K3-SP/OS,
T-H2-DV/OS, T-D2-IN/OS,
T-M32
19 Overheat cut-off fuse 402 EK333
T-K3, T-K3-Pro, T-K3-SP/OS,
T-KJr2-IN/OS, T-K4-IN/OS,
T-D2-IN/OS
20 Heater101 426 EX002 T-D2-IN/OS, T-M32
21 Inlet drain plug (water filter) 437 EX006 T-H2-DV/OS, T-M32
22 Outlet drain plug 442 EKK2E
T-K3, T-K3-Pro, T-K3-SP/OS,
T-KJr2-IN/OS, T-K4-IN/OS,
T-D2-IN/OS
23 Left / Right computer board 701 EM306
24 Central computer board 702 EM307
25 Transformer 718 EM296 T-H2-DV/OS
26 GFl 720 EM207 T-M32
27 Freeze protection thermostat
140 EM286
28 Heater 502 425 EX001
29 Surge box 722 EM385 T-M32
30 Manifold port N/A N/A
31 Gas inlet port N/A N/A

T-M50 / T-M50 ASME Service manual
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5. Schematic diagram
1. When a hot water tap is opened, cold water enters the T-M50.
2. The water flow sensor detects this water flow and sends this information to computer.
3. The computer initiates fan motor and sends signal to igniter to create ignition spark.
4. The main, proportional, and solenoid gas valves open to allow gas input.
5. The gas ignites and flames appear inside the burner chamber.
6. Water circulates through the heat exchanger and is heated up to the set temperature.
7. Using thermistors to measure temperatures, the computer modulates the gas and water valves to
ensure proper output water temperatures.
8. When the tap is closed, the T-M50 shuts down.
Heat
Exchanger
Output
Thermistor
Water
control
valve
Flow sensor
Mixing
Thermistor
Exhaust Output
Thermistor Heat Exchanger
Water control
vale
Flow sensor
Inlet
Thermistor
Computer board
Burner
Gas valve
Fan motor
Fan motor
Hot water
outlet
Cold water
inlet
Gas
Inlet
Thermistor
120 VAC

T-M50 / T-M50 ASME Service manual
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CONFIDENTIAL
6. Wiring diagram
BK:BLACK
P:PURPLE
LB:LIGHT BLUE
BL:BLUE
G;GREEN
Y:YELLOW
O:ORANGE
BR:BROWN
Heater
Thermostat
Inlet
thermistor
Output
thermistor
Mixing
thermistor
BK
BK
BK
GFI
Tra n s-
for m er
12 3 4 5 6
O F F
BR
BR
120 VAC
10A
G
Ground
W
BK BR
Ground
Air-fuel
ratio rod
Ground
Flame
rod
1 2 3 4 5 6
OFF
1 2 3 4 5 6
OFF
MV
SV1
SV2
SV3
Remote
controller
Parent
W
W
IG
Ground
Ground
Inlet
thermistor
Output
thermistor
Mixing
thermistor
BK
BK
BK
12 3 4 5 6
O F F
Air-fuel
ratio rod
Ground
Flame
rod
MV
SV1
SV2
SV3
FM
Igniter
rod
IG
Heater
Heater
Heater
Heater
Heater
7
7
8
8
RYGWBK
BL
ROYGW
BK
BL
RYGW
BK
BL
ROYGW
BK
BL
Water
Control
valve
Water
Control
valve
B K
B K
B K
B K
BK
BK
BK
BK
Y
G
O
O
G
Y
BK B K
W
W
BL
BK
BK
RR
BL
BL
GG
R
BL
Y
O
W
P
PP
PP
PP
P
G
WR B K
W
R
WR B K R
W
BL
LB
G
O
R
W
BK
Y
WBK WBK
BL
LB
G
O
R
BK
W
BK
W
W
BK
BK
W
W
W
W
W
W
W
Gas
Porpor-
tional
Valve
Flow
Sensor
WR BK
W
R
WR BK R
W
Hi-
limit
BL
O.H.C.F
BL
BL BL
BL
FM
R
BL
Y
O
W
BL
Hi-
limit
BL
O.H.C.F
BL
BL B L
BL
BL
Flow
Sensor
Left side unit Right side unit
Surge
box
BK
W
MAX button
MIN button
Increase button
Decrease button
Burning lamp
Communication
lamp (right)
Communication
lamp (left)
Multi-system
on line lamp
Lower bank of
dipswitches
Upper bank of
dipswitches
7 Seg LED
Pump test run
Error call
button
Burning lamp
FM
port
Pump
port
Button to check
unit number
Priority SW
Alarm
contact
Draft switch
Dipswitches
MAX button
MIN button
Increase button
Decrease button
2
1
Dipswitches
Gas
Porpor-
tional
Valve
Igniter
rod
I
F
D1
D2
H1
H1
H2
J
J
E1
E1
E3
E3
E2
E2
CC
A
A
A A
C2
C2
C1
C1
BB
I
N
M
K
A3
A1
A2
L
L
L
L
L
L
L
G G
TM-RE30
H2

T-M50 / T-M50 ASME Service manual
Ver. 1.05
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CONFIDENTIAL
7. Wiring diagram check points for diagnosis
Check-
point
Parts and Description
Color of wires Normal Range
A
A1 100 V Power supply White –Black (A) Brown –Brown (A1) 90 to 110 VAC
A2,A3
120 V Power supply Black - White 108 to 132 VAC
B Igniter Purple –Purple 90 to 110 VAC
Light blue - blue at COM (MV)
78 to 100 VDC (during operation)
/ 0.9 to 1.3 kΩ
Green - blue at COM (SV1) 78 to 100 VDC (during operation)
/ 1.3 to 1.9 kΩ
Orange - blue at COM (SV2) 78 to 100 VDC (during operation)
/ 1.3 to 1.9 kΩ
C Gas valves
Red - blue at COM (SV3) 78 to 100 VDC (during operation)
/ 0.9 to 1.7 kΩ
C1 Hi-Limit switch Blue - Blue
Less than 1 VDC
and
Less than 1 Ω
C2 Overheat cutoff fuse Blue - Blue
Less than 1 VDC
and
Less than 1 Ω
D1 White - White 15 VDC
D2
Easy-link and
Multi-unit link
connectors
Black –Blue
Black –Red
15 VDC
(during Easy-link operation)
E1 Mixing thermistor Black - Black
E2 Output thermistor Black - Black
E3 Inlet thermistor Black - Black
See table on p.12
F Remote controller Black - White 11 to 25 VDC
Red - Blue 110 to 160 VDC
Yellow - Blue 13 to 17 VDC
G Fan motor
Orange - Blue 2 to 6.5 VDC