T-M50 / T-M50 ASME Service manual
Ver. 1.05
18
CONFIDENTIAL
10-4. Gas valve assembly
Unit Part #
Included
in #114
AOS Part #
EM302 (LP model)
EM303 (NA model )
Checkpoint
C,H1
Opens and closes the gas pathways of the water heater (main and solenoid
gas valves)
Function
Modulates the gas flow from the gas inlet (proportional gas valve)
Failure event
1. Gas leak from the valves.
2. Unable to open/close (main and solenoid gas valves)
3. Unable to modulate the gas flow (proportional gas valve)
Effects on the water
heater if valves fails
1. Gas leak from the unit.
2. Excess carbon monoxide emissions. / No flames.
3. Lack of water temperature control.
Error codes when the
valves fails
111
121
510
701
Diagnostic
1. Visual inspection: connection/breakage of wires.
2. Listen for "clunk" sounds from the gas valves opening right after fan motor
initiates.
3. Check voltages and resistance of coils; proper range of values shown
below.
Blue - Light blue (MV) 78 to 100 VDC (during operation) / 0.9 to 1.3 kΩ
Blue - Green (SV
1
)
78 to 100 VDC (during operation) / 1.3 to 1.9 kΩ
Blue - Orange (SV
2
)
78 to 100 VDC (during operation) / 1.3 to 1.9 kΩ
Blue - Red (SV
3
)
78 to 100 VDC(during operation) / 0.9 to 1.7 kΩ
Color/Number of wires
White - Red
(Proportional valve)
1.0 to 15 VDC (during operation) / 20 to 40 Ω
3
-
5
/
8
"
(
9
1
.5
m
m
)
1
-
3
/
8
"
(
3
4
m
m
)
2 - 5 / 8 " ( 6 7 m m )
Proportional valve
Main gas valve
G as
v al ve
4-1/4" (108mm)
7/8" (22.2mm)
4
-
5
/
8
"
(
1
1
9
m
m
)
Solenoid valve
Proportional Valve
EM302 (for LP model) and EM303 (for NA model) is an
assembly of the gas manifold with gas valve assembly.
For safety reasons, these assemblies should be installed
in the unit as a whole set. The diagram below shows the
gas valve assembly.
