Inlet Control Groups FAQs

Ask the Expert: Inlet Control Groups FAQs

In this Q&A feature, we sit down with Stephen Elsmore, Senior Technical Support at Altecnic, to explain the function of each element within an inlet control group, how they work together, and what installers need to know about correct installation, testing, maintenance, and fault-finding.

On this Page:

• Understanding Inlet Control Groups
• Pressure Control & System Operation
• Installation & Commissioning
• Maintenance & Troubleshooting
• Compliance & Best Practice

Understanding Inlet Control Groups

What is an inlet control group?

An inlet control group is a pre-assembled manifold fitted to the cold water supply of an unvented hot water system. It combines several essential control and safety components into one compact unit, reducing installation complexity and helping ensure compliance with Building Regulations, including G3 in the UK.

Its primary role is to regulate, protect and control the cold water entering the system.

What components are typically included?

A standard inlet control group includes:

• Pressure reducing valve (PRV): Limits and stabilises incoming mains water pressure to a preset level, commonly 3 bar.
• Check valve (non-return valve): Prevents water from flowing back from the cylinder into the mains supply.
• Safety relief valve (SRV): Provides final protection if system pressure rises above safe limits, typically 6 bar.
• Strainer/filter: Included on most models to help prevent debris from entering the valve.

These components are factory-matched to work together at specific pressure settings.

Pressure Control & System Operation

Why is pressure regulation important?

Mains pressure can be too high or inconsistent for unvented systems. Excessive pressure can damage cylinders, valves and downstream components, while stable pressure helps improve appliance performance and reduce wear.

The PRV ensures the system operates within its designed pressure range regardless of fluctuations in the incoming supply.

How do the components work together?

The inlet control group operates as a pressure management sequence:

1. The PRV reduces and stabilises incoming mains pressure.
2. The check valve prevents reverse flow and maintains system integrity.
3. The relief valve protects against abnormal pressure rise.

If the safety relief valve operates, excess pressure is safely discharged to drain via a tundish.

Installer Tip: Regular discharge indicates a system fault and should never be ignored.

Installation & Commissioning

Where should an inlet control group be installed, and what should installers consider?

The inlet control group must be installed:

• On the cold water supply pipe.
• Upstream of the unvented hot water cylinder.
• After the main isolation valve.
• In the direction of flow indicated on the valve body.

Installers should also ensure:

• Correct orientation and flow direction.
• Relief valve discharge is piped to a safe, visible drain point.
• Adequate space is left for servicing and replacement.
• Pipework is properly supported to avoid strain on the manifold.

Most units can be installed horizontally or vertically, provided access is maintained for inspection and servicing.

Always follow both the inlet control group and cylinder manufacturer’s instructions.

What should be checked during commissioning?

During commissioning and routine servicing:

• Confirm correct downstream pressure after the PRV.
• Check for leaks at compression joints.
• Inspect the relief valve discharge pipe for signs of operation.
• Verify isolation valves function correctly.

Any unexplained discharge or pressure instability should be investigated immediately.

Maintenance & Troubleshooting

What maintenance is required?

Although inlet control groups are largely maintenance-free, periodic checks are recommended:

• Inspect the filter/strainer for debris, if serviceable.
• Check relief valve discharge for signs of frequent activation.
• Confirm pressure remains within specification.

Servicing should be carried out by a qualified engineer as part of regular system maintenance.

What are common faults and how can they be identified?

Reduced flow rate

Possible causes include:

• Blocked strainer.
• Debris in the PRV.

Frequent safety relief valve discharge

Possible causes include:

• Failed PRV.
• Loss of pre-charge in the expansion vessel.
• Incorrect expansion vessel installation.
• Excessive incoming pressure.

Noise or vibration

Possible causes include:

• Incorrect installation orientation.
• High flow velocity.
• Pressure fluctuations.

Early diagnosis helps prevent component failure and system downtime.

What should an installer do if the safety relief valve keeps discharging?

Frequent safety relief valve discharge should always be investigated rather than treated as normal operation.

Installers should check:

• PRV operation.
• Incoming mains pressure.
• Expansion vessel pre-charge.
• Expansion vessel installation.
• Any other pressure-related faults within the system.

Repeated discharge can indicate an underlying system fault and should be resolved before it leads to further component or system issues.

Compliance & Best Practice

Why are inlet control groups essential for compliance?

Inlet control groups help ensure unvented systems meet safety and regulatory requirements by:

• Controlling pressure at the point of entry.
• Preventing backflow into the mains.
• Providing visible pressure relief in fault conditions.

Correct selection, installation and maintenance are essential to system safety and long-term performance.