Mitsubishi Electric EHWT17D-MHEDW, Data Book

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No. Fault symptom Possible cause Explanation - Solution
7 No water at hot tap. 1. Cold main off 1. Check and open stop cock.
2. Strainer (local supply) blocked. 2. Isolate water supply and clean strainer.
8 Cold water at tap. 1. Hot water run out. 1. Ensure DHW mode is operating and wait for DHW tank to re-heat.
2. Prohibit, schedule timer or holiday mode se-
lected or demand control input (IN4) or smart
grid ready (switch-off command).
2. Check settings and change as appropriate.
3. Heat pump not working. 3. Check heat pump.
4. Booster heater cut-out tripped. 4. 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 "7.5.1 Component parts" to find out its position.
5. The earth leakage circuit breaker for booster
heater breaker (ECB1) tripped.
5. Check the cause and reset if safe.
6. The booster heater thermal cut-out has
tripped and cannot be reset using the manual
reset button.
6. 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.
7. Immersion heater cut-out tripped. 7. Check immersion heater thermostat and press reset button, located on im-
mersion heater boss, if safe. If the heater has been operated with no water
inside it may have failed, so please replace it with a new one.
8. Immersion heater breaker (ECB2) tripped.
8. Check the cause and reset if safe.
9. 3-way valve fault 9. Check plumbing/wiring to 3-way valve.
(i) Manually override 3-way valve using the main remote controller. (Refer to
<Manual operation> in "7.7 System setup") If the valve does not still func-
tion, go to (ii) below.
(ii) Replace 3-way valve coil. If the valve does not still function, go to (iii) be-
low.
(iii) Replace 3-way valve. (Refer to Service manual.)
9 Water heating takes
longer.
1. Heat pump not working. 1. Check heat pump.
2. Booster heater cut-out tripped. 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 "7.5.1 Component parts" to find out its position.
3. Booster heater breaker (ECB1) tripped.
3. Check the cause and reset if safe.
4. The booster heater thermal cut-out has
tripped and cannot be reset using the manual
reset button.
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. Immersion heater cut-out has been triggered. 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. Immersion heater breaker (ECB2) tripped. 6. Check the cause and reset if safe.
7. Flow rate of the sanitary circuit may be reduced. 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 Service
manual.)
• Replace plate heat exchanger (water - water) or scale trap, if there are a
blockage which blocks the sanitary circuit.
10 Temperature of DHW
tank water dropped.
When DHW operation is not running, the DHW
tank emits heat and the water temperature de-
creases to a certain level. If water in the DHW tank
is reheated frequently because of a significant
drop in water temperature, check for the following.
1. Water leakage in the pipes that connect to
the DHW tank
1. Take the following measures.
• Retighten the nuts holding the pipes onto the DHW tank.
• Replace seal materials.
• Replace the pipes.
2. Insulation material coming loose or off. 2. Fix insulation.
3. 3-way valve failure 3. Check plumbing/wiring to 3-way valve.
(i) Manually override 3-way valve using the main remote controller. (Refer to
<Manual operation> in "7.7 System setup".) 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 Service manual.)
4. Water pump (sanitary circuit) speed setting
failure
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.
11 Hot or warm water
from cold tap.
Heat of hot water pipe is transferred to cold water
pipe.
Insulate/re-route pipework.
12 Water leakage 1. Poorly sealed connections of water circuit
components
1. Tighten connections as required.
2. Water circuit components reaching the end of
life
2. Refer to PARTS CATALOG for expected part lifetimes and replace them as
necessary.
B-256
Water to Water Heat Pump (WTW)
7
Cylinder
unit/
Hydrobox/GSHP/WTW