What is a Closed System?

A closed system is a heating or cooling system where the water goes round and round without being exposed to air. Think of radiators or air conditioning chillers.

Because the water does not get fresh air, it can cause rust and sludge inside the pipes. BG50 tells you how to prevent this.

Cleaning New Systems

New systems must be cleaned before they are used. This removes:

• Dirt from building work (flux, metal shavings, oil)
• Rust
• Any bugs in the water

The Cleaning Steps

1. Flush - Push water through fast to remove loose dirt
2. Chemical clean - Add cleaning chemicals and circulate them
3. Protect - Add a coating to stop rust forming
4. Rinse - Flush out the cleaning chemicals
5. Add chemicals - Put in rust inhibitor and bug killer

What Chemicals to Use

Rust Inhibitors

These coat the inside of pipes to stop rust:

• Sodium molybdate (common in heating systems)
• Sodium nitrite (another option)

Oxygen Removers

These take oxygen out of the water (oxygen causes rust):

• Sodium sulphite

Bug Killers (Biocides)

Used in cooling systems or where bugs are found.

What to Check

Heating Systems - Check Every 3 Months

• Chemical levels
• pH
• How well the water conducts electricity (TDS)
• Iron (shows if there is rust)
• What the water looks like

Cooling Systems - Check Every 3 Months

• All the same things as heating
• Plus bacteria testing

Common Problems

• Air getting in - Through expansion vessels or leaks
• Rust under dirt - Caused by sludge or biofilm
• Scale - In hard water areas
• Bugs - Bacteria growing in the system
• Mixed metals - Different metals touching can cause rust