Mitsubishi Electric EHST20C-VM6HA Service Manual page 52

No. Fault symptom
Duration is set to excessively short time at "Economy setting for
3 Heating mode has been
pump". (Go to "Service menu" → "Auxiliary setting" → "Economy
on standby for a long
setting for pump").
time (does not start
operation smoothly.)
The 3-way valve may have foreign objects in it, or hot water
4 Heating emitter is hot
may flow to the heating side due to malfunctions.
in the DHW mode.
(The room temperature
rises.)
The cylinder unit is designed to run in an operation mode with a
5 The cylinder unit that
higher priority (i.e. DHW mode in this case) at power recovery.
was running in the
heating mode before
power failure is running
in the DHW mode after
power recovery.
10-6. Checking Component Parts' Function
Water circulation pump
L
Immersion heater
Possible cause
Part Name
N
M
1~
Explanation - Solution
Set "Economy setting for pump" longer.
Manually override the 3-way valve several times to check whether
the problem will be solved. (Refer to the service manual.) If the
problem persists replace the 3-way valve coil with a new one. If
still no change replace the entire 3-way valve with a new one.
• Normal operation.
• After the DHW max. operation time has elapsed or the DHW
max. temperature has been reached, the DHW mode switches
to the other mode (ex. Heating mode).
Check Points
Measure the resistance between the terminals with a tester.
(Winding temperate 20 °C)
Terminal Normal
121Ω
L - N
<Water circulation pump characteristics>
80
70
60
50
40
30
20
Speed2
10 Speed1
0
0 10 20
Flow rate [L/min]
<Recommended water flow rate range>
Outdoor heat pump unit
Packaged
PUHZ-W50
PUHZ-W85
PUHZ-HW11
PUHZ-HW140
Split PUHZ-RP35
PUHZ-RP50
PUHZ-RP60
PUHZ-(H)RP71
PUHZ-(H)RP100
PUHZ-(H)RP125
PUHZ-RP140
* I f the water flow rate is less than 7.1 L/min, the flow switch will be activated.
If the water flow rate exceeds 27.7 L/min, the flow speed will be greater than
1.5 m/s, which could corrode the pipes.
Measure the resistance between the terminals with a tester.
(Winding temperate 20°C)
Terminal Normal
19.2 Ω
A-B
To reset the immersion heater use a pin or similar to press the reset button
located on the top of the immersion boss.
See diagram on the left.
5
Abnormal
Open or Short
Speed3
(Default setting)
30 40
Water flow rate range [L/min]
7.1 - 14.3
10.0 - 5.8
14.4 - 7.7
17.9 - 7.7
7.1 - 11.8
7.1 - 17.
8.6 - 0.1
10. - .9
14.4 - 7.7
17.9 - 7.7
0.1 - 7.7
Abnormal
Open or Short