Velux CLI U12 SD0W118 El B/U Installation Operation & Maintenance page 51

Nature of trouble
Pump does not operate (even
though there is solar radiation and
the tank is cold).
Pump operates intermittently.
System pressure too high.
System pressure too low.
Temperature differential between
collector and storage tank too
high.
Pump operates at night.
Storage tank cools down rapidly.
Possible cause
No power to pump.
Controller improperly set.
Sensor out of position.
Sensor defective.
Pump defective.
Normal when weather changes.
Sensors connected to wrong terminals.
Improper system "switch-on" or "switch-off" temperature.
Sensor out of position.
Filling pressure too high.
Expansion tank initial pressure too high.
Expansion tank too small.
Propylene glycol leak in system.
Expansion tank too small (release of propylene glycol from
relief valve).
Controller improperly set or sensor defective.
Controller improperly set.
Sensor out of position.
No power to pump.
Air or impurities present in system.
Pump defective.
Normal on very warm nights.
Check valve open or dirty.
Controller defective.
Consumption higher than design for system.
Check valve open or dirty.
Insulation defective or inadequate.
Service
Check controller and pump wiring.
Check program - Refer to pump station
manual "Control parameter" section.
Check position of all sensors.
Check sensor resistance - Refer to controller
manual "Tips for Fault Localization" section.
Replace pump.
None.
Check sensor connections - Refer to
controller manual "Installation" section.
Check sensor resistance - Refer to controller
manual "Control parameter" section.
Secure sensor properly.
Adjust system pressure to 50 psi (3.5 bar).
Isolate and adjust expansion tank to 40 psi
(2.8 bar).
Properly size and replace expansion tank.
Check system for leaks and repair.
Properly size and replace expansion tank.
Check program - Refer to controller manual
"Control parameter" section.
Check program - Refer to controller manual
"Control parameter" section.
Secure sensor properly.
Check controller and pump wiring.
Properly commission system, purge all air.
Replace pump.
None.
Check position of check valves, clean or
replace if necessary.
Replace controller.
Reduce rate of hot water use.
Check position of check valves, clean or
replace if necessary.
Add, repair, or replace pipe insulation as
needed.
Part 7: Troubleshooting – 51