Mitsubishi Electric EHST20C-VM6HA Service Manual page 53

Part Name
Booster heater
Thermostat (90 °C) and thermal cut out (121 °C)
121 °C 90 °C
Manual reset
Thermal
water
cut-out
thermostat
9 10
2kW heater (230V, 1 phase)
2kW
1 2
2 + 4kW heater (230V, 1 phase)
2kW
2kW
3 4 1
3 + 6kW heater (400V, 3 phase)
2kW
2kW 2kW
4 5 6 1
Earth leakage breaker for heater
Relay for heater R S T A1 A2
U V W
Flow switch
Flow
Thermistors
Measure the resistance between the terminals with a tester.
2kW
2
1kW
1kW 1kW
2 3
If a short circuit occurs on the booster heater, immersion heater, or each power line, a short-circuit
breaker will trip and power source will be blocked.
Eliminate the causes of short circuit and then turn on the breaker again.
When the applied voltage is not 230V AC across the terminals A1-A2, check the terminals R-U,
S-V, and T-W are open.
When the applied voltage is 230V AC across the terminals A1-A2, check the terminals R-U, S-V,
and T-W are short.
Measure the resistance between the terminals with a tester.
1
2
Paddle vertical (Flow < 5.5 l/min)
Paddle inclined (Flow > 5.5 l/min)
3
Disconnect the connector then measure the resistance with a tester.
(At ambient temperatures of 10 - 30°C.)
TH1
TH
THW1
THW
THW5B
THW3
Check Points
Terminal Normal
110(±35)mΩ
9-10
Terminal Normal
26.5(+3/-1.3)Ω
1-
Terminal Normal
26.5(+3/-1.3)Ω
1-
13.3(+1.5/-0.6)Ω
3-4
Terminal Normal
105.8(+11.8/-5)Ω
1-=-3=1-3
52.9(+5.8/-2.5)Ω
4-5=5-6=4-6
State of moving part
Thermistor Normal
4.3 - 9.5 kΩ
160 - 410 kΩ
53
Abnormal
Open or Short
Abnormal
Open or Short
Abnormal
Open or Short
Open or Short
Abnormal
Open or Short
Open or Short
Normal Abnormal
Open Other than open
Short Other than short
Abnormal
Open or short