Mitsubishi Electric EHPT20Q-VM2EA Service Manual page 45

No. Fault symptom
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 cylinder unit compo-
nents 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 cylinder 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.
3. Heating circuit is closed and pump is running.
18 Noisy water circulation Air in water circulation pump.
pump
19 Noise during hot 1. Loose airing cupboard pipework.
water draw off
typically worse in the
2. Air in water circulation pump A.
morning.
20 Mechanical noise 1. Heaters switching on/off.
heard coming from
the cylinder unit.
2. 3-way valve changing position between
DHW and heating mode.
21 Water circulation Water circulation pump jam prevention mechanism
pump runs for a short (routine) to inhibit the build-up of scale.
time unexpectedly.
22 Milky/Cloudy water Oxygenated water
(Sanitary circuit)
23 Heating mode has The time of "Delay" set in "Economy settings
been on standby for for pump" is too short. (Go to "Service menu"
a long time (does
not start operation pump").
smoothly.)
24 The cylinder unit The cylinder unit is designed to run in an operation
that was running in mode with a higher priority (i.e. DHW mode in this
the heating mode case) at power recovery.
before power failure
is running in the
DHW mode after
power recovery.
GCH15010
Possible cause Explanation - Solution
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 9-4). 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 11. 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.
2. Open the heating circuit.
Use manual and automatic air vents to remove air from system.
Top up water if necessary to achieve 1 bar on primary circuit.
1. Install extra pipe fastening clips.
2.
Use manual and automatic air vents to remove air from system.
Top up water if necessary to achieve 1 bar on primary circuit.
Normal operation no action necessary.
Normal operation no action necessary.
Water from any pressurised system will release oxygen bubbles when water is
running. The bubbles will settle out.
Increase the time of "Delay" in "Economy settings for pump" .
After the DHW max. operation time has elapsed or the DHW supply max.tem-
perature has been reached, the DHW mode switches to the other mode
(e.g. Heating mode).
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