Vaillant geoTHERM Installation Instructions Manual page 101

Fault code Error text/description
28 Coolant pressure too low
Brine side/well water side is
supplying too little heat.
The integral low pressure switch
has tripped at 125 kPa (1.25 bar)
(g).
29 Coolant pressure outside the
range
If the error occurs twice in a
row the heat pump cannot be
started until after 60 min. at
the earliest.
11.3 Fault with temporary switch-off
Installation instructions geoTHERM 0020051574_04
Fault diagnosis and rectification
Possible cause
(VWS only) Air in the brine circuit.
Brine fluid concentration too low.
(VWS only) The pump output of the
brine pump has dropped or the brine
pump is faulty.
(VWS only) Not all circuits are circu-
lating equally. Can be seen from the
difference in the severity of icing on
individual brine circuits.
Not all the required stop valves are
open.
Coolant flow rate too low (e.g. ther-
mal expansion valve TEV incorrectly
adjusted or faulty).
For VWS/VWW 38/2 and 46/2 only:
The fault relay on the in-rush cur-
rent limiter has responded.
The red LED on the in-rush current
limiter is flashing:
2x = Incorrect phase sequence
3x = Compressor motor overcurrent
4x = Thyristor module excess tem-
perature
5x = Low voltage/phase failure
6x = Min./max. power frequency
7x = No compressor connected
Coolant pressure too high or too low,
all causes mentioned at fault 27 and
28 are possible..
Solution
> Bleed the brine circuit.
> Check the brine fluid frost protection and
increase the brine concentration if necessary.
> Check the brine pump, and replace if neces-
sary.
> Adjust the brine circuits.
> Open all stop valves.
> Have the coolant circuit checked. Inform the
factory customer service department.
> Check whether the green LED on the in-rush
current limiter is lit. If the green LED is not
lit, there is no power supply or the in-rush
current limiter is faulty.
> Check the power supply and restore.
> Check the in-rush current limiter and inform
the factory customer service department if
necessary.
> VWS/VWW 38/2 and 46/2 only:
If the green LED lights up and red LED is
flashing, find the cause in the list of flash
codes above and rectify the fault, and inform
the factory customer service department if
necessary.
See faults 27 and 28.
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