Viessmann VITOCAL 250-A - Page 100

100
F.3 Lead break, return temperature sensor
F.3
System characteristics
■
No defrost
■
No room cooling
Cause
Lead break, secondary circuit return temperature sen-
sor
Measures
1. Check connection X4.3/X4.4 on the EHCU electron-
ics module:
■
Check wires and plugs for correct seating.
■
Check connections for contact corrosion.
■
Check cables for mechanical damage, e.g. crush-
ing, kinking, chafing or breakage.
2. Check resistor R for NTC 10 kΩ on the disconnected
plug. If R > 300 kΩ, replace the sensor.
3. Replace EHCU electronics module.
F.4 Short circuit, return temperature sensor
F.4
System characteristics
■
No defrost
■
No room cooling
Cause
Short circuit, secondary circuit return temperature sen-
sor
Measures
1. Check the sensor and connection X4.3/X4.4 on
the EHCU electronics module:
■
Check wires and plugs for correct seating.
■
Check connections for contact corrosion.
■
Check cables for mechanical damage, e.g. crush-
ing, kinking, chafing or breakage.
2. Check resistor R for NTC 10 kΩ on the disconnected
plug. If R < 500 Ω, replace the sensor.
3. Replace EHCU electronics module.
F.7 Lead break, cylinder temperature sensor
F.7
System characteristics
■
Only room heating
■
No DHW heating
Cause
Lead break, cylinder temperature sensor
Measures
1. Check the connection:
Wall mounted indoor unit:
Connection on underside of the appliance, 6-pole
connection socket on the right, terminals 9 and 10
(plug 5 on HPMU electronics module)
Floorstanding indoor unit:
Connection X3.3/X3.4 (plug 5) on the HPMU elec-
tronics module
■
Check wires and plugs for correct seating.
■
Check connections for contact corrosion.
■
Check cables for mechanical damage, e.g. crush-
ing, kinking, chafing or breakage.
2. Check resistor R for NTC 10 kΩ on the disconnected
plug. If R > 300 kΩ, replace the sensor.
3. Replace HPMU electronics module.
F.8 Short circuit, cylinder temperature sensor
F.8
System characteristics
■
Only room heating
■
No DHW heating
Cause
Short circuit, cylinder temperature sensor
Messages
Fault messages (cont.)
6218234
Diagnosis