Velux CLI U12 SD0W118 El B/U User Manual (English)

Questions and Answers:

A
Andrew ChaseAug 20, 2025
What to do if my Velux CLI U12 SD0W118 El B/U doesn't produce enough hot water?
- D
  destinywilliamsAug 20, 2025
  If your Velux Water System isn't providing enough hot water, several issues could be the cause. The system might be undersized, in which case you should reduce the rate of hot water use. A defective element (check amperage and replace if necessary) or thermostat (check wiring or replace) could also be to blame. Also check for leaking plumbing or open hot water faucets, making sure all faucets are closed and checking the water meter. Finally, the solar system controller may be incorrectly installed, so check the installation.
B
Beverly WeaverAug 22, 2025
How to adjust the temperature of my Velux CLI U12 SD0W118 El B/U if the water is too hot or not hot enough?
- C
  Christopher MckeeAug 22, 2025
  If the water from your Velux Water System is either too hot or not hot enough, the thermostat setting might be too high or low; change the setting as required. Alternatively, the thermostat might be out of calibration, in which case you should replace it. A grounded element can also cause this issue, requiring replacement. Also, the solar system may be incorrectly installed, so check the installation.
D
Daniel Martin MDAug 25, 2025
How to reduce high pressure in my Velux Water System?
- A
  Amber FloresAug 26, 2025
  If the pressure in your Velux Water System is too high, it could be due to a filling pressure that's too high; adjust the system pressure to 50 psi (3.5 bar). Alternatively, the expansion tank initial pressure might be too high; isolate and adjust the expansion tank to 40 psi (2.8 bar). The expansion tank might also be too small; properly size and replace the expansion tank.
M
Michelle WilliamsAug 28, 2025
What causes low pressure in a Velux CLI U12 SD0W118 El B/U Water System?
- E
  Edward HatfieldAug 28, 2025
  Low pressure in your Velux Water System can stem from a few potential causes. A propylene glycol leak in the system is one possibility; check the system for leaks and repair them. Another cause could be an expansion tank that's too small, leading to the release of propylene glycol from the relief valve; properly size and replace the expansion tank. Finally, the controller may be improperly set or the sensor may be defective. Check the program.
J
Jessica KellyAug 30, 2025
Why does my Velux CLI U12 SD0W118 El B/U storage tank cool down so quickly?
- L
  Lori ArmstrongAug 30, 2025
  A Velux Water System storage tank that cools down rapidly may be experiencing consumption higher than the system's design; reduce the rate of hot water use. Another possible cause is a check valve that is open or dirty; check the position of the check valves, and clean or replace them if necessary. Inadequate or defective insulation can also lead to rapid cooling; add, repair, or replace pipe insulation as needed.
A
Alexander SmithSep 2, 2025
Why is there a high temperature difference between the collector and storage tank in my Velux CLI U12 SD0W118 El B/U Water System?
- M
  Mark PorterSep 2, 2025
  A high temperature differential between the collector and storage tank in your Velux Water System can occur due to several reasons. The controller might be improperly set, so check the program. The sensor could also be out of position; secure the sensor properly. Other potential causes include no power to the pump (check controller and pump wiring), air or impurities present in the system (properly commission the system and purge all air), or a defective pump (replace the pump).
J
Jennifer BeasleySep 4, 2025
What to do if the pump in my Velux CLI U12 SD0W118 El B/U isn't working despite solar radiation?
- S
  Stephen BryantSep 4, 2025
  If the pump in your Velux Water System isn't operating even with solar radiation and a cold tank, there might be no power to the pump; check the controller and pump wiring. The controller could also be improperly set; check the program. Other potential issues include a sensor out of position (check the position of all sensors), a defective sensor, or a defective pump (replace the pump).
P
Philip AndersonSep 6, 2025
Why does the pump in my Velux Water System run intermittently?
- T
  Trevor BurtonSep 7, 2025
  Intermittent pump operation in your Velux Water System can be normal when the weather changes. However, it could also be due to sensors connected to the wrong terminals; check the sensor connections. An improper system “switch-on” or “switch-off” temperature could also be the cause. Another reason may be that the sensor is out of position; secure the sensor properly.
Z
zpetersonSep 9, 2025
Why is the pump in my Velux CLI U12 SD0W118 El B/U Water System running at night?
- J
  johnmillerSep 9, 2025
  The pump in your Velux Water System running at night can be normal on very warm nights. However, it could also be due to a check valve that is open or dirty; check the position of check valves, and clean or replace if necessary. A defective controller can also cause this issue; replace the controller.

Velux CLI U12 SD0W118 El B/U Specifications

General

Brand	Velux
Model	CLI U12 SD0W118 El B/U
Category	Water System
Language	English

Summary

Part 1: Product and Safety Information

Definitions and Hazard Warnings

Defines hazard symbols (DANGER, WARNING, CAUTION) and important terms used in the manual.

Installation and Temperature Safety

Covers local regulations, installer qualifications, and risks associated with high water temperatures.

Part 2: General Information

System Overview and Components

Introduces the system, its performance factors, and details on collectors, tanks, and piping.

Pump Station and System Balance

Explains the pump station controller, sensors, and other balance of system components.

Part 3: Solar Water Heater System Installation

Installation Preparation and Checklist

Provides a comprehensive checklist covering all aspects of system installation.

System Types and Component Installation

Illustrates system configurations and details installation of core components like collectors, tanks, and pumps.

Piping, Connections, and Commissioning

Covers piping, electrical, gas, boiler connections, system charging, and commissioning.

Controller Setup and Operation

Explains how to program and operate the system controller.

Part 4: Maintenance

Maintenance, Shutdown, and Lifespan

Lists maintenance tasks, shutdown procedures, vacation planning, and component lifespan.

Part 5: Specifications

Collector, Tank, and Pump Station Specs

Lists features, dimensions, and technical data for collectors, tanks, and pump stations.

Heat Transfer Fluid and Emergency Overview

Provides technical data for the heat transfer fluid, including safety and pH testing.

Part 6: Component Lists

VELUX Solar System Kit Components

Breaks down the components included in different VELUX solar system kits by model number.

Part 7: Troubleshooting

System Problems, Solutions, and Labels

Lists common issues, causes, solutions, and SRCC OG-300 labeling instructions.

Pump and Pressure Troubleshooting

Addresses pump operation, system pressure issues, and rapid tank cooling troubleshooting.

Service Information

Installer and Installation Details

Fields to record installer contact information and system installation specifics for service.

Velux CLI U12 SD0W118 El B/U User Manual

Table of Contents