Viessmann VITOCAL 250-A - Page 155

155
Measures
1. Check the sensor and the following connections:
■
Terminals X17.1/X17.2 on EHCU electronics mod-
ule
■
Wall mounted indoor unit:
6-pole connection socket on underside of appli-
ance on left, terminals 5 and 6
■
Floorstanding indoor unit:
Extra low voltage (ELV) terminal area < 42 V,
lower luster terminal, terminals 7 and 8
■
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.997 Lead break, temperature sensor in cooling water buffer cylinder
F.997
System characteristics
No cooling of external cooling water buffer cylinder
Cause
Only for heat pumps with 1 integral heating/cooling cir-
cuit:
Lead break, temperature sensor in cooling water buffer
cylinder
Measures
1. Check the following connections:
■
Terminals X17.1/X17.2 on EHCU electronics mod-
ule
■
Wall mounted indoor unit:
6-pole connection socket on underside of appli-
ance on left, terminals 5 and 6
■
Floorstanding indoor unit:
Extra low voltage (ELV) terminal area < 42 V,
lower luster terminal, terminals 7 and 8
■
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.998 Communication error, refrigerant circuit controller to EHCU/flow rate signal
F.998
System characteristics
The refrigerant circuit will not start.
Cause
■
Signal fault, flow sensor
■
No communication between EHCU electronics mod-
ule and VCMU refrigerant circuit controller for at
least 5 s.
Messages
Fault messages (cont.)
6218234
Diagnosis