By Audrey HayesUpdated November 2026
Anyone maintaining a flushing solar hot water system needs equipment that can move fluid through collectors and storage without fuss, and that can be serviced when scale, sediment or air starts to slow things down. This list focuses on the parts most often used to flush, circulate and control a solar hot water loop: controllers, pumps and a complete closed-loop kit. The selection criteria were compatibility with pressurized and closed-loop designs, electrical simplicity for a DIY installer, pump flow and head suited to residential loops, and documented brand reputation. The picks were assessed from product specifications and general owner feedback patterns, not from hands-on testing.
Our top picks at a glance
- 1
TOP CHOICEBest overallSolar Water Heating System Skyline5 Closed LoopView on Amazon - 2
TOP CHOICEBest for split pressurized loopsMISOL 110V Controller of Solar Water HeaterView on Amazon - 3
TOP CHOICEBest for small kitchens and compact tanks200 Liter Water Heater Active Split System Single Coil TankView on Amazon - 4
Best budget pickMini Inline 12V DC Solar Water Heater Circulation PumpView on Amazon - 5
Best for flushing and drain-down workEngineering Plastics Six Impeller Submersible Water PumpView on Amazon
Our Top Picks
Quick Comparison
| Product | Best for | Key feature |
|---|---|---|
| Solar Water Heating System Skyline5 Closed Loop | Complete closed-loop installs | Closed-loop design with matched components |
| MISOL 110V Controller of Solar Water Heater | Pressurized split systems | 110V controller for pump and sensor management |
| 200 Liter Water Heater Active Split System Single Coil Tank | Small kitchens and compact tanks | Single coil tank with evacuated tube compatibility |
| Mini Inline 12V DC Solar Water Heater Circulation Pump | Budget circulation and flushing loops | 12V DC operation, 3.5 GPM flow, 19.6 ft lift |
| Engineering Plastics Six Impeller Submersible Water Pump | Flushing and drain-down tasks | Brushless DC motor, 800 L/h flow |
Solar Water Heating System Skyline5 Closed Loop
Solar Water Heating System Skyline5 Closed Loop
Best for: Complete closed-loop installs where the collector, pump and fluid circuit need to work as one system.
This suits homeowners who want a packaged closed-loop arrangement rather than sourcing every component separately. Closed-loop designs are the usual choice when freezing is a concern, because they circulate a heat-transfer fluid rather than potable water.
Key specs:
- Closed-loop heat-transfer design
- Intended for residential solar hot water circuits
Pros:
- Matched components reduce guesswork on pump and loop sizing
- Closed loop suits cold-climate installs
- Single-source kit simplifies ordering and troubleshooting
Cons:
- Requires careful fluid handling and periodic fluid checks
- Less flexible if you want to mix in your own components
Bottom line: The most complete starting point for someone building a closed-loop flushing and circulation setup from one kit.
MISOL 110V Controller of Solar Water Heater
MISOL 110V Controller of Solar Water Heater, Used for Separated pressurized Solar hot Water System
Best for: Pressurized split systems that need a controller to run the pump and react to temperature differences.
Installers who are adding or replacing the control side of a split pressurized loop will find this type of controller most relevant. Because the controller decides when the pump runs, it is central to any flushing cycle you schedule.
Key specs:
- 110V mains operation
- Designed for pressurized separated solar hot water systems
Pros:
- Matches a common mains-powered control scheme
- Clear purpose for split pressurized loops
- Simple to integrate with a standard circulation pump
Cons:
- Wiring requires basic electrical competence and code compliance
- Sensor and pump compatibility must be checked before purchase
Bottom line: The right pick if your loop is split and pressurized and you need dedicated control logic.
200 Liter Water Heater Active Split System Single Coil Tank
200 Liter Water Heater Active Split System Single Coil Tank 45 Deg Frame Evacuated Vacuum Tubes Hot SRCC Certified
Best for: Small kitchens and compact tanks where floor space and storage volume are limited.
This is a storage tank with a single coil for heat exchange, aimed at active split systems. It suits households with modest hot water demand that want a compact footprint.
Key specs:
- 200 liter storage volume
- Single coil heat exchanger
- Listed for evacuated tube compatibility
Pros:
- Compact 200 liter capacity fits small spaces
- Single coil keeps plumbing layout simple
- Active split design suits pump-driven flushing
Cons:
- Capacity may be tight for larger households
- Coil flow rate and connections need to match your collector loop
Bottom line: A sensible choice for small households and tight utility rooms that run an active split loop.
Mini Inline 12V DC Solar Water Heater Circulation Pump
for Hot/Cold Water Circulation System, RV Water Heater, Pool Heating & Homebrew Wort Transfer, 3.5 GPM 19.6 FT Lift 12V DC Solar Water Heater Circulation Pump, Mini Inline Water Pump
Best for: Budget circulation and flushing loops that run on low-voltage DC power.
A small inline pump is a practical way to move fluid through a short loop for flushing, priming or circulation. Owners often use pumps like this for RV and pool work as well, so it is worth confirming the head and flow match your loop.
Key specs:
- 12V DC operation
- 3.5 GPM flow rate
- 19.6 ft maximum lift
Pros:
- Low-voltage DC suits solar-powered circuits
- Compact inline form factor is easy to fit
- Stated flow and lift give a clear sizing reference
Cons:
- Not designed as a heavy-duty commercial flushing pump
- Lift and flow drop with restrictive piping and fittings
Bottom line: A good budget option for a short, low-head flushing or circulation loop on a 12V system.
Engineering Plastics Six Impeller Submersible Water Pump
Engineering Plastics Six Impeller Design, Body, for Toilet Flushing Systems and Solar Hot Water Circulation Submersible Water Pump Black Dc 19w Brushless 800l/h Flow
Best for: Flushing and drain-down tasks where a submersible pump moves water out of a tank or sump.
This submersible unit is listed for toilet flushing and solar hot water circulation. It suits people who need to pump out a tank or push flushing water through a loop from a reservoir.
Key specs:
- DC brushless motor, 19 W
- 800 L/h flow rate
- Engineering plastics body with six-impeller design
Pros:
- Brushless DC motor is quiet and efficient
- Submersible design suits tank and reservoir flushing
- Plastic body resists corrosion in water service
Cons:
- Flow is modest compared with larger circulators
- Intake screens need regular cleaning to prevent clogging
Bottom line: Best for hands-on flushing and drain-down work from a tank or sump rather than continuous high-head circulation.
Buying Guide
Loop Type: Open, Closed or Split Pressurized
Start by identifying your loop type, because it determines which components are compatible. Closed loops circulate a heat-transfer fluid, open loops circulate potable water, and split pressurized systems separate the storage tank from the collector circuit. Match your pump and controller to that design before anything else.
Good picks for this: Solar Water Heating System Skyline5 Closed Loop, MISOL 110V Controller of Solar Water Heater
Pump Flow and Head
Flow rate (liters or gallons per minute) and head or lift (how high the pump can push water) must both suit your loop. Check the stated maximum lift against the vertical height of your collector and piping, then allow margin for friction losses from fittings and long runs.
Good picks for this: Mini Inline 12V DC Solar Water Heater Circulation Pump, Engineering Plastics Six Impeller Submersible Water Pump
Voltage and Power Source
Decide whether the pump will run on 12V DC from a small panel and battery or on 110V AC from mains. Low-voltage DC pumps suit off-grid or PV-driven circuits, while mains-powered controllers and pumps need proper wiring and a dedicated circuit. Mixing voltages without the right converter is a common source of failure.
Good picks for this: Mini Inline 12V DC Solar Water Heater Circulation Pump, MISOL 110V Controller of Solar Water Heater
Storage Tank Size and Coil Design
Tank volume should reflect your daily hot water use, and the coil must be sized to transfer heat from the collector loop at a practical rate. A single coil keeps plumbing simple, while larger households may need more volume or a second storage stage.
Good picks for this: 200 Liter Water Heater Active Split System Single Coil Tank
Materials and Corrosion Resistance
Look at the wetted materials in pumps and fittings. Engineering plastics and stainless components resist scale and corrosion better than basic metals, especially where the loop sees mineral-rich water or flushing solutions. Confirm that fluid compatibility is listed for any closed-loop fluid you plan to use.
Good picks for this: Engineering Plastics Six Impeller Submersible Water Pump, Solar Water Heating System Skyline5 Closed Loop
Serviceability and Access
Flushing is maintenance work, so choose components you can reach, isolate and drain. Valves, unions and accessible pump housings make service far easier than sealed assemblies. Plan isolation valves before the pump so you can service it without draining the whole system.
Good picks for this: Mini Inline 12V DC Solar Water Heater Circulation Pump, Engineering Plastics Six Impeller Submersible Water Pump
Installation Skill and Code Compliance
Electrical work and pressurized plumbing carry real risk. Confirm local plumbing and electrical code requirements before installing controllers or pumps, and use a licensed professional for mains wiring or any work that affects potable water. Consult a professional if you are unsure.
Good picks for this: MISOL 110V Controller of Solar Water Heater, Solar Water Heating System Skyline5 Closed Loop
FAQ
What does flushing a solar hot water system involve?
Flushing means running clean water or an approved cleaning solution through the collector and piping to remove sediment, scale and air. It is usually done with a circulation pump, isolation valves and a drain point. Follow the manufacturer’s procedure, because some closed-loop fluids must be drained and replaced rather than simply flushed.
How often should a solar hot water loop be flushed?
Frequency depends on water quality, loop type and fluid. Many installers recommend checking fluid condition and flushing on a schedule set by the manufacturer, often annually in hard-water areas. Check the specifications for your specific equipment rather than relying on a general rule.
Can I use a standard water pump for flushing a closed loop?
Only if the pump’s wetted materials and flow rating are compatible with the heat-transfer fluid and the loop’s head requirements. Closed-loop fluids can be incompatible with some plastics and seals. Confirm compatibility with the manufacturer before using any pump.
What flow rate do I need for a residential loop?
Flow requirements depend on collector area, piping diameter and the design flow the manufacturer specifies for your collectors. Compare the pump’s stated flow and lift against your loop’s calculated requirements, and allow margin for pipe friction and fittings.
Is a 12V DC pump enough for a full solar hot water loop?
It can be sufficient for short, low-head loops and smaller systems, but larger or taller installations may need a more powerful pump. Check the stated lift and flow against your piping run before deciding.
Do I need a controller if I already have a pump?
In most active systems, yes. A controller reads temperature differences and decides when the pump runs. Without one, the loop may circulate at the wrong times, which wastes energy or can damage components. Confirm your controller and pump are designed to work together.
What safety precautions apply when flushing?
Isolate the system, relieve pressure, and use appropriate protective equipment. Hot fluid and pressurized piping can cause burns or injury. If your system is pressurized, electrical, or connected to potable water, consult a licensed professional before working on it.
Conclusion
For a complete closed-loop build, the Solar Water Heating System Skyline5 Closed Loop is the most integrated starting point. Pressurized split systems are better served by the MISOL 110V Controller of Solar Water Heater. Small households with limited space should look at the 200 Liter Water Heater Active Split System Single Coil Tank, while the Mini Inline 12V DC Solar Water Heater Circulation Pump fits budget short-loop work. For drain-down and tank flushing tasks, the Engineering Plastics Six Impeller Submersible Water Pump is the most targeted option. Match each pick to your loop type, head requirement and voltage before buying.
Sources
- Federal guidance on solar water heating types, components and system design (energy.gov)
- Research on solar thermal system performance and maintenance considerations (nrel.gov)
- Plumbing and mechanical code standards that govern pressurized water systems
Related reading
- What's the Best Solar Hot Water System? 3 Top Picks Compared (2026)
- What Is the Cheapest Solar Hot Water System? Options and Trade-Offs
- Top 5 Solar Thermal Storage Tanks for Home Hot Water Systems
About Audrey Hayes
Audrey Hayes is part of our editorial team and reviews and edits our solar water heaters guides, checking product details against manufacturer specifications and owner feedback.
