HOW TO STAY COMPLIANT WITH WATER REGULATIONS USING THE RIGHT PRESSURISATION SOLUTION
What is a Sealed Heating System?
A sealed heating (or unvented) system is closed to atmosphere and operates under pressure. These systems are now standard across both residential and commercial applications, including chilled systems.
To function correctly, they require a pressurisation unit to:
- Fill the system
- Maintain system pressure
- Replace water losses
- Protect the incoming mains water supply
Understanding Fluid Categories
Under the Water Supply (Water Fittings) Regulations, heating systems are categorised based on risk:
- Fluid Category 3 (Domestic / House)
A slight health hazard (e.g. water containing low levels of additives) - Fluid Category 4 (Non-Domestic / Commercial)
A significant health hazard due to chemicals such as corrosion inhibitors, biocides, and system debris
In simple terms: If it’s not a house, it’s almost certainly Fluid Category 4.
Common Mistakes in the Industry
Despite clear guidance, we frequently see:
- Filling loops left permanently connected
- Systems installed with insufficient backflow protection
- Devices that cannot fill a system from empty
- Lack of consideration for low mains pressure scenarios
These issues can lead to non-compliance, potential water contamination, and long-term system inefficiencies.
Domestic Systems (Fluid Category 3)
For residential properties:
- A temporary filling loop with a double check valve can be used
- However, it must be disconnected after use to remain compliant
Modern alternatives offer a safer, more convenient solution:
- CA Filling Valve
- Permanently connected
- No electrical power required
- Automatically maintains system pressure
- Mechanical PRV systems (e.g. CA15C573PRV)
- Electronic AutoFill units (e.g. AFCA15)
Non-Domestic Systems (Fluid Category 4)
For commercial and non-house installations:
- A minimum Fluid Category 4 backflow prevention device is mandatory
- Filling loops must not be used
This is where correct specification becomes critical.
Arrow Valves Solutions – These fill, as well as pressurise the system designing out the need for a quick fill loop.
Auto-Fill Units (AFS15 / AFS22)
- Incorporate RPZ (Type BA) valves
- Require annual testing in line with regulations
AFP Units (AFP15 / AFP22)
- Include a boost pump for low mains pressure environments
Midi-Fill Digital (MFD15 / MFD22)
- Offers Fluid Category 5 protection
- Intelligent monitoring and alert systems
- Capable of both filling and maintaining systems
Dose & Fill Units (DF15 / DF22)
- Combine pressurisation with automatic chemical dosing
- Maintain correct inhibitor levels over time
- Help prevent corrosion and extend system lifespan
Why Correct Specification Matters
Water Regulations are in place to protect:
- Public health
- Mains water supply integrity
- System efficiency and longevity
With increasing focus on compliance and enforcement, choosing the right solution is no longer optional, it’s essential.
Final Thought
Not all pressurisation units are created equal.
Some will only maintain pressure, others, like Arrow Valves solutions, are designed to fully fill, protect, and future-proof your system.
Need support with specification or compliance?
Contact the Arrow Valves team to discuss your project.