48
Page
240 (T-H3J), 340 (T-H3S) and 540 (T-H3) models Service Manial
Ver. 1.00
CONFIDENTIAL
Natural of Fault
Diagnosis
Check
point
• The hot water turns
cold and stays cold
1 Check whether the flow rate is high enough to keep the water heater
running.
2 Check if there is a recirculation system installed and check also if the
recirculation line has enough check valves.
3 Check that the filter on the cold water inlet is clean.
4 Check that the fixtures are free from debris and obstructions.
• The fan motor is
still spinning after
operation has stopped
1 This is normal operation. After operation has stopped, the fan motor
keeps its running 15 to 70 seconds in order to re-ignite quickly, as
well as purge all the exhaust gas out of the flue.
• Abnormal sound
from water heater
1 Check the gas type of the water heater.
2 Check how long the water heater has been installed and in use.
3 Check the installation place.
4 Check the altitude/elevation of area of where the water heater
installed.
5 Check the vent length, when the water heater has been installed
indoors.
6 Check if there is any blockage in the intake air and/or exhaust.
7 Check if there is dust and lint in burner and heat exchanger, when
the water heater has been installed in laundry room.
8 Check if there is grease and dirt in burner and fan motor, when the
water heater has been installed in restaurant.
9 Check the manifold pressure in the water heater.
Natural of Fault
Diagnosis
Check
point
• Fluctuation of hot
water temperature
1 Check whether the filter in cold water inlet is cleaned.
2 Check whether the gas supply pressure is adequate.
3 Check for cross connections between cold water lines and
hot water lines.
4 Fault of PCB in the water heater
[1] No voltage to gas solenoid valve (SV
1
).
Normal: 93 to 120 VDC between COM (blue) & #9 (green)
(during operation)
[2] No voltage to gas solenoid valve (SV
3
).
Normal: 93 to 120 VDC between COM (blue) & #73 (red)
(during operation)
C
5 Gas solenoid valve (SV
1
) fault
[1] Disconnected wiring to gas solenoid valve (SV
1
)
Normal: 1.35 to 1.65 kΩ between COM (blue) & #9 (green)
[2] Disconnected wiring to gas solenoid valve (SV
3
)
Normal: 2.07 to 2.53 kΩ between COM (blue) & #73 (red)
C