Mitsubishi Electric EHSD-MED Service Manual page 52

No. Fault symptom
9 Water heating takes 1. Heat pump not working
longer.
2. Booster heater cut-out tripped.
3. Booster heater breaker (ECB1) tripped.
4. The booster heater thermal cut-out has
tripped and cannot be reset using the manual
reset button.
5. Immersion heater cut-out has been triggered.
6. Immersion heater breaker (ECB2) tripped.
10 Temperature of DHW When DHW operation is not running, the DHW
tank water dropped. tank emits heat and the water temperature
decreases to a certain level. If water in the DHW
tank is reheated frequently because of a signifi-
cant drop in water temperature, check for the
following.
1. Water leakage in the pipes that connect to the
DHW tank
2. Insulation material coming loose or off
3. 3-way valve failure
11 Hot or warm water Heat of hot water pipe is transferred to cold water
from cold tap. pipe.
12 Water leakage 1. Poorly sealed connections of water circuit
components
2. Water circuit components reaching the end of
life
13 Heating system does 1. Prohibit, schedule timer or holiday mode se-
not reach the set lected or demand control input (IN4) or smart
higher temperature. grid ready (switch-off command).
2. Check settings and change as appropriate.
3. The temperature sensor is located in a room
that has a different temperature relative to that
of the rest of the house.
4. Heat pump not working
5. Booster heater cut-out tripped.
6. Booster heater breaker (ECB1) tripped.
7. The booster heater thermal cut-out tripped and
cannot be reset using the manual reset button.
8. Incorrectly sized heat emitter
9. 3-way valve failure
10. Battery problem (*wireless control only)
11. If a mixing tank is installed, the flow rate
between the mixing tank and the hydrobox is
less than that between the mixing tank and
the local system.
14 Heating system does The heating system operates according to the
not reach the set heating pressure to prevent the low pressure
lower temperature. system from frequent switching (ON/OFF) of the
compressor.
OCH712C
Possible cause Explanation - Solution
1. Check heat pump – consult outdoor unit service manual.
2. Check booster heater thermostat and press reset button if safe.
Reset button is located on the side of booster heater, covered with white rub-
ber cap. See "4. PART NAMES AND FUNCTIONS" to find out its position.
3. Check the cause and reset if safe.
4. Check resistance across the thermal cut-out, if open then connection is
broken and the booster heater will have to be replaced.
Contact your Mitsubishi Electric dealer.
5. Check immersion heater thermostat and press reset button if safe. If the
heater kept running with no water inside, this may have resulted in failure, so
replace it with a new one.
6. Check the cause and reset if safe.
1. Take the following measures.
• Retighten the nuts holding the pipes onto the DHW tank.
• Replace seal materials.
• Replace the pipes.
2. Fix insulation.
3. Check plumbing/wiring to 3-way valve.
(i) Manually override 3-way valve using the main remote controller. (Refer
to <Manual operation> in "9-4. Service Menu".) If the valve does not still
function, go to (ii) below.
(ii) Replace 3-way valve.
Insulate/re-route pipework.
1. Tighten connections as required.
2. Refer to PARTS CATALOG in the service manual for expected part lifetimes
and replace them as necessary.
1. Check settings and change as appropriate.
2. Check the battery power and replace if flat.
3. Relocate the temperature sensor to a more suitable room.
4. Check heat pump – consult outdoor unit service manual.
5. Check booster heater thermostat and press reset button if safe.
Reset button is located on the side of booster heater, covered with white rub-
ber cap. (See "4. PART NAMES AND FUNCTIONS" for position.)
6. Check the cause of the trip and reset if safe.
7. Check resistance across the thermal cut-out, if open then the connection is
broken and the booster heater will have to be replaced.
Contact your Mitsubishi Electric dealer.
8. Check the heat emitter surface area is adequate
Increase size if necessary.
9. Check plumbing/wiring to 3-way valve.
10. Check the battery power and replace if flat.
11. Increase the flow rate between the mixing tank and the hydrobox or
decrease that between the mixing tank and the local system.
Normal operation, no action necessary.
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