Mitsubishi Electric EHST17D-YM9D Service Manual page 59

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.
7. Flow rate of the sanitary circuit may be reduced.
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
4. Water pump (sanitary circuit) speed setting
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
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 be-
tween the mixing tank and the cylinder unit is
less than that between the mixing tank and
the local system.
OCH714B
Possible cause
59
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 bro-
ken and the booster heater will have to be replaced.
Contact your Mitsubishi Electric dealer.
5. Check immersion heater thermostat and press reset button located on immer-
sion heater boss, 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.
7. Check the following items
• Check for trapped air in water pump (sanitary circuit).
• Check if the speed of water pump (sanitary circuit) is set to 2.
• Check water pump (sanitary circuit) for malfunction. (Refer to "10-6.
Checking Component Parts' Function".)
• Replace plate heat exchanger (water - water) or scale trap, if there are a
blockage which blocks the sanitary circuit.
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 "9-5. Service menu".) If the valve does not still func-
tion, go to (ii) below.
(ii) Replace 3-way valve motor. If the valve does not still function, go to (iii)
below.
(iii) Replace 3-way valve. (Refer to "11. DISASSEMBLY PROCEDURE".)
4. Water pump (sanitary circuit) MUST be set to speed 2.
When it set to speed 1, hot water would be mixed with cold water due to
circulation.
Insulate/re-route pipework.
1. Tighten connections as required.
2. Refer to PARTS CATALOG 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 bro-
ken 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.
(i) Manually override 3-way valve using the main remote controller. (Refer to
<Manual operation> in "9-5. Service menu".) If the 3-way valve does not func-
tion, go to (ii) below.
(ii) Replace 3-way valve motor. If the 3-way valve coil is replaced but the
3-way valve does not function go to (iii) below.
(iii) Replace 3-way valve. (Refer to "11. DISASSEMBLY PROCEDURE".)
10. Check the battery power and replace if flat.
11. Increase the flow rate between the mixing tank and the cylinder unit decrease
that between the mixing tank and the local system.