Mitsubishi Electric EHGT17D-YM9ED Service Manual page 54

No. Fault symptom
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
between the mixing tank and the unit is less
than that between the mixing tank and the
local system.
14 In 2-zone tempera- 1.
ture control, only
Zone2 does not
reach the set tem-
2.
perature.
3.
4.
5.
15 After DHW operation At the end of the DHW mode operation the 3-way
room temperature valve diverts hot water away from the DHW circuit
rises slightly. into space heating circuit.
This is done to prevent the unit components from
overheating.
The amount of hot water directed into the space
heating circuit varies according to the type of the
system and of the pipe run between the plate heat
exchanger and the unit.
16 The room tempera- 3-way valve failure
ture rises during DHW
operation.
17 Water discharges 1. If continual – pressure relief valve could bite
from pressure relief foreign objects and the valve seat may be
valve. damaged.
(Primary circuit)
2. If intermittent – expansion vessel charge may
have reduced/bladder perished.
18 Water discharges 1. If continual – field supplied pressure reducing
from pressure relief valve not working.
valve.
2. If continual – pressure relief valve could bite
(Sanitary circuit)
foreign objects and the valve seat may be
damaged.
3. If intermittent – expansion vessel charge may
have reduced/bladder perished.
4. DHW tank may have subjected to backflow.
19 Noisy water Air in water circulation pump.
circulation pump
OCH722A
Possible cause
When Zone1 and Zone2 are both in heating
mode, the hot water temperature in Zone2
does not exceed that in Zone1.
Faulty wiring of motorized mixing valve
Faulty installation of motorized mixing valve
Incorrect setting of Running time
Motorized mixing valve failure
Explanation - Solution
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.
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 "3. 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 "8-5. 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 "10. DISASSEMBLY PROCEDURE".)
10. Check the battery power and replace if flat.
11. Increase the flow rate between the mixing tank and the unit decrease that
between the mixing tank and the local system.
1. Normal action no action necessary.
2. Refer to installation manual, "5.3 Wiring for 2-zone temperature control".
3. Check for correct installation. (Refer to the manual included with each mo-
torized mixing valve.)
4. Check for correct setting of Running time.
5. Inspect the mixing valve. (Refer to the manual included with each motorized
mixing valve.)
Normal operation no action necessary.
Check the 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 3-way valve does not
function, go to (ii) below.
(ii) Replace 3-way valve coil. 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 "10. DISASSEMBLY PROCEDURE".)
1. Turn the handle on the pressure relief valve several turns. If leakage persists,
replace the pressure relief valve with a new one.
2. Check pressure in expansion vessel.
Recharge to 1 bar if necessary.
If bladder perished replace expansion vessel with a new one.
1. Check function of pressure reducing valve and replace if necessary.
2. Turn the handle on the pressure relief valve several turns. If leakage persists,
replace the pressure relief valve with a new one.
3. Check gas-side pressure in expansion vessel.
Recharge to correct precharge pressure if necessary.
If bladder perished replace expansion vessel with a new one with appropriate
pre-charge.
4. Check the pressure in DHW tank. If pressure in DHW tank is similar to that in
the incoming mains, cold water supply that merges with incoming mains wa-
ter supply could flow back to DHW tank. Investigate source of back-feed and
rectify error in pipework/fitting configuration. Adjust pressure in cold supply.
Use manual and automatic air vents to remove air from system.
Top up water if necessary to achieve 1 bar on primary circuit.
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