Closed systems.

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What are closed system water treatment and maintenance services?

Closed system water treatment focuses on maintaining the water quality within sealed heating and cooling systems such as chilled water, LTHW, and condenser circuits. These systems can experience serious issues if corrosion, scale, or microbiological fouling are left unmanaged — leading to reduced efficiency, leaks, and costly equipment damage.

At Complii, we deliver closed system water hygiene and maintenance programmes in line with BSRIA BG50:2021, BS 8552, and ACoP L8. Our services ensure corrosion, scale, and biofilm are effectively controlled, supporting long-term system performance, safety, and compliance. Through proactive testing, analysis, and treatment, we help facilities teams maintain clean, balanced, and efficient closed systems.

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Why choose Complii?

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Protect your people, property, and business. Here’s why we’re the right choice for closed systems.

Prevents corrosion and scale build-up

Our water treatment programmes control oxygen ingress, pH balance, and inhibitor concentration to stop corrosion and scale before they cause damage to components and pipework.

Maintains system efficiency

Clean, well-balanced systems transfer heat efficiently, improving performance and reducing energy costs across both heating and cooling networks.

Controls microbiological growth

We monitor and manage bacterial contamination including Pseudomonas, Sulphate Reducing Bacteria (SRB), and Nitrite Reducing Bacteria (NRB), preventing fouling and under-deposit corrosion.

Compliant with BSRIA and HSE standards

All monitoring and maintenance activities are carried out in line with BSRIA BG50:2021, BS 8552, and HSG274, providing a fully auditable compliance record.

Reduces long-term repair and replacement costs

Regular maintenance extends the lifespan of pumps, valves, and boilers, minimising disruption, downtime, and capital expenditure.

Detailed analysis and reporting

Quarterly bacteriological and chemical testing provides actionable data on corrosion potential, inhibitor performance, and bacterial activity, supported by expert recommendations.

Your questions answered.

A closed system is a sealed heating or cooling circuit where the same water circulates continuously. These systems include chilled water loops, LTHW heating networks, and condenser circuits.
Even though they are sealed, closed systems can suffer from corrosion, scaling, and microbiological fouling over time. Regular water treatment prevents these issues, protecting equipment and maintaining efficiency.
According to BS 8552, closed systems should undergo chemical and bacteriological sampling every three months, or more frequently in high-risk or problematic systems.
Typical bacterial issues include Pseudomonas, Sulphate Reducing Bacteria (SRB), and Nitrite Reducing Bacteria (NRB). These organisms can cause corrosion, fouling, and gas generation within the system.
Indicators include changes in commissioning results, discolouration of water (reddish or muddy), greasy films on strainers, poor heat transfer, or pressure fluctuations.
Yes. If test results show elevated corrosion or bacterial levels, we provide chemical cleaning, flushing, and re-inhibition to restore system balance and protect long-term performance.

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Compliance with confidence.

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