Heater solar water 2
Assistant Tank is an essential solar accessory designed for automatic cold water loading in non-pressurized solar water heaters. Made with food-grade SUS304 stainless steel and high-density PU insulation, it delivers reliable performance, excellent hygiene, and a long service life for both residential and commercial solar systems.
Assistant Tank is a key solar accessory designed for automatic cold water loading in non-pressurized solar water heaters. With SUS304 food-grade material and high-density PU insulation, it ensures stable performance, hygiene, and long service life.

The Stainless Steel Assistant Tank is an essential solar accessory designed to automatically load cold water into the main solar water heater tank. It ensures stable water supply, protects the system from dry burning, and eliminates the need for manual water filling. Ideal for non-pressurized solar water heaters, apartment installations, rural households, and commercial solar water heating solutions.
| Assistant Tank Technical Parameters | ||
| Specification | Details | |
| Capacity Options | 3L, 5L, 8L, 10L, 12L, 15L, 20L | |
| Inner Tank Material | Food-grade Stainless Steel SUS304-2B | |
| Outer Shell | SUS304-2B / BA Food-grade Stainless Steel | |
| Insulation Layer | High-Density PU Foam | |
| Float Ball | Stainless Steel SUS304 | |
| Seal Material | High-temperature Resistant Silicon Seal | |
| Tank Seat | Thick Rubber Base with Arc-Shaped Design | |
| Valve Shaft | Brass | |
✔ Automatic cold water loading – no manual filling required
✔ Food-grade stainless steel – safe and long-lasting
✔ Energy-saving solar accessory – improves solar heater efficiency
✔ High-density PU insulation – prevents heat loss
✔ Silicon seal prevents leakage at high temperatures
✔ Available in multiple capacities for different system sizes
The float ball mechanism automatically regulates the water level:
As hot water is used, the water level drops.
The float ball drops and opens the valve.
Cold water flows in automatically.
When full, the float ball closes the valve.
⚙ Working principle similar to a toilet cistern, simple and reliable!

Basically, non-pressurized solar water heaters have two main types of cold water loading methods:
A small tank (3 L, 5 L, or 15 L), typically side-mounted or top-mounted on the main water tank. Its primary function is to refill the main tank with cold water. When hot water is drawn, the assistant tank ensures that cold water is gradually added, preventing the main tank from running dry.
An electronic control unit that monitors water temperature and water level via built-in sensors. It can automatically operate solenoid valves, pumps, or electric heating elements to manage cold water loading, trigger backup heating when needed, and maintain safe operation by preventing dry-heating, over-temperature, and potential leaks.

● Non-pressurized solar water heaters
● Residential solar water heating systems
● Hotels & resorts
● Farmhouses & rural areas
● Solar projects requiring automated water loading


● Easy installation
● No electrical parts required
● Universal design fits most solar heaters
● Long service life with SUS304 stainless steel
An assistant tank is a key solar accessory used in non-pressurized solar water heaters. It automatically loads cold water into the main tank through a float ball system, ensuring a stable water level and preventing dry burning.
If you want automatic water loading without manual filling, then an assistant tank is necessary. It’s especially recommended for homes, hotels, and solar projects where daily manual water filling is not convenient.
Our assistant tanks are made of food-grade SUS304 stainless steel, with high-density PU insulation and silicon seal resistant to high temperatures, making them safe, durable, and hygienic for long-term use in solar water heating systems.
Our assistant tanks are made of food-grade SUS304 stainless steel, with high-density PU insulation and silicon seal resistant to high temperatures, making them safe, durable, and hygienic for long-term use in solar water heating systems.
| What is the difference between an assistant tank and a solar controller ? | ||
| Feature | Assistant Tank | Solar Controller (TK-7 / TK-8A / M-7 / M-8) |
| Water Loading Method | Mechanical float system | Electronic sensor + solenoid valve |
| Power Required | No | Yes (electricity needed) |
| Maintenance | Very low | Requires periodic setting & checking |
| Cost | More affordable | Higher cost |
| Automation Level | Basic automatic system | Full smart control |
| Suitable For | Simple solar heaters | Advanced solar projects / hotels |
The assistant tank is a cost-effective solar accessory for basic non-pressurized solar water heaters, while the solar controller offers smarter control, temperature display, and timed water feeding—suitable for high-end systems or commercial applications.
RIWATT provides OEM & ODM services for all capacities.
Logos, packing boxes, color customization available on request.
📦 MOQ: Flexible for mixed orders
🌍 Exported to: Southeast Asia, Latin America, Africa, Europe
⚙ Suitable for solar project bidding & installation kitsIdeal upsell in solar accessories package


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