Mitsubishi Electric EHGT17D-YM9ED Service Manual page 53

No. Fault symptom
7 No water at hot tap. 1. Cold main off
2. Strainer (local supply) blocked.
8 Cold water at tap. 1. Hot water run out.
2. Prohibit, schedule timer or holiday mode se-
lected or demand control input (IN4) or smart
grid ready (switch-off command).
3. Heat pump not working.
4. Booster heater cut-out tripped.
5. The earth leakage circuit breaker for booster
heater breaker (ECB1) tripped.
6. The booster heater thermal cut-out has
tripped and cannot be reset using the manual
reset button.
7. Immersion heater cut-out tripped.
8. Immersion heater breaker (ECB2) tripped.
9. 3-way valve fault
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 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
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
OCH722A
Possible cause
53
Explanation - Solution
1. Check and open stop cock.
2. Isolate water supply and clean strainer.
1. Ensure DHW mode is operating and wait for DHW tank to re-heat.
2. Check settings and change as appropriate.
3. Check heat pump.
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 "3. PART NAMES AND FUNCTIONS" to find out its position.
5. Check the cause and reset if safe.
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. 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. Check the cause and reset if safe.
9. Check plumbing/wiring to 3-way valve.
(i) Manually override 3-way valve using the main remote controller. (Refer to
<Manual operation> in "8-5. Service menu") 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 "10. DISASSEMBLY PROCEDURE".)
1. Check heat pump.
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 "3. 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 "9-6. Check-
ing 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 "8-5. 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 "10. 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.