Mitsubishi Electric EHSC-VM6A Service Manual page 44

No. Fault symptom
12 Heating system does 1. Prohibit, schedule timer or holiday mode selected.
not get up to set tem-
2. Check settings and change as appropriate.
perature.
3. The room in which the temperature sensor is located is at a
4. Heat pump not working.
5. Booster heater cut out has triggered.
6. Booster heater breaker (ECB1) has tripped.
7. The booster heater thermal cut-out has operated and can
8. Incorrectly sized radiators
9. 3-way valve (2-way valve) (fi eld supply) fault
10. Battery problem *wireless control only
13 After DHW operation At the end of the DHW mode operation the 3-way valve (2-way
room temperature valve) (field supply)diverts hot water away from the hydrobox
rises a little. into space heating circuit.
This is done to prevent the hydrobox components from overheating.
The amount of hot water directed into the space heating circuit
is dependent on the type of system and the pipe run between
the plate heat exchanger and the hydrobox.
14 The room temperature 3-way valve (2-way valve) (fi eld supply) fault
rises during DHW
operation.
15 Water discharges from 1. If continual – pressure relief valve seat may be damaged.
pressure relief valve.
2. If intermittent – expansion vessel charge may have
(Primary circuit)
3. System was excessively pressurised at fi ll stage.
4. Unit has overheated – thermal controls have failed.
16 Water discharges from 1. If continual – fi eld supplied pressure reducing valve not working.
pressure relief valve.
(Sanitary circuit)
2. If continual – pressure relief valve seat may be damaged.
3. If intermittent – expansion vessel charge may have
4. Unit is being back pressurised.
18 Noisy pump Air in pump.
19 Noise during hot water Loose airing cupboard pipework.
draw off typically Heaters switching on/off.
worse in the morning.
20 Mechanical noise 1.
heard coming from the
2.
hydrobox.
21 Pump runs for a short Pump jam prevention mechanism to inhibit the build up of scale. Normal operation no action necessary.
time for no reason.
22 Milky/Cloudy water Oxygenated water
(Sanitary circuit)
23 Heating mode has been Duration is set to excessively short time at "Economy setting for
pump". (Go to "Service menu" → "Auxiliary setting" → "Economy
on standby for a long
setting for pump").
time (does not start
operation smoothly.)
24 Heating emitter is hot 1.
in the DHW mode.
(The room temperature
rises.)
2.
Possible cause
different temperature to the rest of the house.
not be reset using the manual reset button.
reduced/bladder perished.
reduced/bladder perished.
Heaters switching on/off.
3-way valve (fi eld supply) changing position between DHW
and heating mode.
The 3-way valve may have foreign objects in it, or hot
water may fl ow to the heating side due to malfunctions.
2-way valve (fi eld supply) has tripped.
1. Check settings and change as appropriate.
2. Check the battery power and replace if fl at.
3. Reposition 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 covered with white rubber cap see component
parts diagram section 10-6. for position.
6. Check the cause of the trip and reset if safe.
7. Check the resistance of the thermal cut out, if 0 then the
connection is broken and the booster heater will have to be
replaced.
Please contact your Mitsubishi Electric dealer.
8. Contact installer
9. Check plumbing/wiring to 3-way valve (2-way valve) (fi eld
supply).
10. Check the battery power and replace it fl at.
Normal operation no action necessary.
Check the 3-way valve (2-way valve) (fi eld supply).
1. Remove cartridge – check seat and renew if necessary.
2. Check pressure in expansion vessel.
Recharge to 1 bar if necessary.
If bladder perished replace vessel.
3. Ensure the fi ll connection has been physically DISCONNECT-
ED from the mains water supply. With hydrobox cold check
pressure in hydrobox. If necessary, discharge/re-fi ll system to
the recommended cold-fi ll pressure of 1 bar.
4. Switch off power to the heat pump. Leave water supply on.
Wait until discharge stops. Isolate water supply and replace if
faulty.
1. Check function of pressure reducing valve and replace if
necessary.
2. Remove cartridge – check seat and renew if necessary.
3. Check pressure in expansion vessel.
Recharge to correct precharge pressure if necessary.
If bladder perished replace vessel.
4. With cylinder cold, check pressure in cylinder. If this is the
same as the incoming mains pressure then you are getting
back feed. Install a balanced cold supply.
Use manual and automatic air vents to release excess air from
system. Top up water if necessary to achieve 1bar on primary
circuit.
Install extra pipe fastening clips.
Normal operation no action necessary.
Water from any pressurised system will release oxygen bubbles
when fl owing. The bubbles will settle out.
Set "Economy setting for pump" longer.
1. Manually override the 3-way valve several times to check
whether the problem will be solved. (Refer to the service
manual.) If the problem persists replace the 3-way valve coil
with a new one. If still no change replace the entire 3-way
valve with a new one.
2. Check the cause of the trip and check plumbing/wiring to
2-way valve (fi eld suppl).
44
Explanation - Solution