62 Installation and maintenance instructions 0020244997_07
Code/meaning Possible cause Measure
F.68 Fault: Flame signal un-
stable
Flame monitor reports an un-
stable flame signal
▶ Check: Air ratio, gas flow pressure, condensate route (block-
age), gas injector, ionisation flow (cable, electrode), flue gas
recirculation.
F.70 Fault: Invalid Device Spe-
cific Number
Incorrect/missing Device
Specific Number or
incorrect/missing coding resistor
▶ If the display and PCB have been replaced, change the Device
Specific Number under D.93.
F.71 Fault: Flow temperature
sensor
Flow temperature sensor re-
turns implausible values
▶ Check: Flow temperature sensor (correct thermal connection).
F.72 Fault: Flow/return temper-
ature sensor
Temperature difference
between flow and return
temperature sensor is too great
▶ Check: Flow temperature sensor/return temperature sensor
(function, correct thermal connection).
F.73 Fault: Water press. sensor
(signal too weak)
Water pressure sensor reports
that the water pressure is too
low
▶ Check: Water pressure, earth connection, cable, plug, water
pressure sensor (short circuit to GDN).
F.74 Fault: Water press. sensor
(signal too strong)
Water pressure too high 1. Drain water.
2. Check the water pressure sensor.
F.75 Fault: Pump/ water short-
age
Insufficient pressure jump de-
tected when starting the pump
1. Check: Water pressure sensor, heating pump (blockage),
heating circuit (air, sufficient water volume), adjustable by-
pass, external expansion vessel (must be connected at the
return). Activate check programme P.0.
2. If a low loss header or heating pipes with a diameter greater
than 1 1/2 inch are installed, replace the 3/4-inch seal in
the heating flow with a screen. If required, install the F.75
service set.
F.77 Fault: Flue non-ret.
valve/condens. pump
No flue non-return flap feed-
back; condensate pump over-
flow
▶ Check: Cable to VR40 accessory, flue non-return flap (wiring,
feedback switch), condensate pump, bridge from the surface-
mounted thermostat, 2 in 7 multi-functional module (bridge).
F.78 Interruption: DHW outlet
sensor at ext. control
UK link box is connected
without the domestic hot water
temperature sensor being
bridged
1. Check: Accessory (configuration/electrical connection).
2. The unit displays a fault, but the unit has not malfunctioned.
F.80 Fault: actoSTOR inlet
sensor
Inlet temperature sensor defect-
ive or not connected
▶ Check (only in conjunction with F.91): NTC sensor, plug, cable
harness, PCB.
F.81 Fault: cylinder charging
pump
Cylinder is not fully charged
after specified time
▶ Check (only in conjunction with F.91): Cylinder charging
sensor, cylinder sensor, impeller sensor/limiter, prioritising
diverter valve, pump, actoSTOR pump (air), cable harness,
secondary heat exchanger (blockage).
F.82 Fault: Ext. current anode External current anode defect-
ive or not connected
▶ Check: Cable harness, external current anode. If the external
current anode is not installed: Plug edge connector X43 with a
bridge into the PCB.
F.83 Fault: NTC temp. gradient Temperature difference
between flow and return
temperature sensor is too small
▶ Check: Flow/return temperature sensor (function, correct
thermal connection), sufficient water volume.
F.84 Fault: NTC temp. diff. im-
plausible
Temperature difference is im-
plausible
▶ Check: Flow/return temperature sensor (correct thermal con-
nection, sensors are inverted).
F.85 Fault: NTCs fitted incor-
rectly
Flow/return temperat-
ure sensors returning
incorrect/implausible values
▶
Check: Flow/return temperature sensor (correct thermal con-
nection).
F.90 Fault: Communication Communication with actoSTOR
interrupted
1. Check: Plug, check cable harness to the actoSTOR module
(PEBus).
2. If the product is to be operated without an actoSTOR:
Set D.092=0, if required, plug edge connector X31 into
the BMU, if required plug edge connector X1 into the
actoSTOR.
F.91 Fault: actoSTOR sensor Sensor on the actoSTOR is
defective
▶ Check: Plug, cable harness, sensor.
F.92 Fault: Incorrect gas type The coding resistor on the PCB
does not match the gas group
that is entered
1. Check: Coding resistor.
2. Carry out the gas family check again and enter the correct
gas group.
F.93 Fault: Check gas route Combustion quality outside the
permitted range
▶ Check: Gas injector (suitable for the gas group), flue gas re-
circulation, gas group, internal pressure measuring point in the
Venturi (blockage). Do not use any lubricants on the O-ring in
the Venturi.
F.94 Fault: Vortex and differen-
tial pressure
Sensors return implausible val-
ues.
▶ Check: Cable harness, plug, sensors.
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