Diagram of a standard radiator - what are the key components?

Radiators play a really important role in heating homes across the UK, particularly in systems powered by a central boiler. If you're new to how hot water radiators work, understanding the main components can be really helpful. Whether you're upgrading your heating system or just curious, this beginner-friendly guide explains the key parts you'll find in a typical radiator and what each one does.

In this article we look at the main components of a standard central heating radiator and give a brief explanation of what they do.

1. Radiator Body (Panel)

The radiator panel is the large, flat metal surface you see on your wall. It’s usually made of steel and is where most of the heat comes from. Inside, hot water flows through channels, warming the panel, which then radiates heat into the room. Some models have a single panel; others have two or three for greater heat output.

• Further reading: How Do Radiators Work? A Complete Guide

2. Convector Fins

Convector fins are thin, corrugated metal sheets attached to the back of the panel (or between panels). They help increase the radiator’s surface area and boost heat transfer. Cold air from the room enters at the bottom, passes over the warm fins, and rises out the top as heated air. Convector fins can come in single rows or double rows.

• Further reading: What's The Difference Bewteen Type 11, 21 And 22 Radiators?

3. Top Grille

The top grille is the slotted or louvered cover that runs along the upper edge of the radiator. It’s mainly decorative, hiding the convector fins and helping guide warm air upwards into the room. You’ll often find it on double panel radiators with internal convector fins.

• Further reading: What's The Difference Between Compact, Round Top and Seam Top Radiators?

4. Side Panels

These are the flat covers on the left and right ends of the radiator. They provide a neat, enclosed finish by hiding the internal components and pipework. Like the top grille, they’re mostly for appearance, but also offer a layer of safety.

5. Inlet Valve (Flow Valve)

This valve is where hot water from your boiler enters the radiator. It’s usually located at one of the bottom corners. It controls how much water flows into the radiator and can be adjusted manually or automatically, depending on the type of valve used.

• Further reading: How To Tell The Inlet and Outlet On Your Radiator

6. Thermostatic Radiator Valve (TRV)

A TRV is a type of inlet valve fitted with a numbered control head. It senses the room temperature and automatically adjusts the water flow into the radiator to maintain your preferred comfort level. This helps save energy and keeps the room at a steady heat.

• Further reading: How Do Thermostatic Radiator Valves Work?

7. Manual Valve

A manual valve allows you to control the radiator by turning it by hand. It’s a simple on/off or high/low adjustment, without any automatic temperature regulation. It’s often used in smaller spaces or rooms where consistent manual control is preferred.

• Further reading: A Complete Guide To Radiator Valves

8. Outlet Valve (Return Valve / Lockshield Valve)

This valve sits at the opposite end of the radiator to the inlet. It controls how quickly cooler water leaves the radiator and returns to the central heating system. It’s typically adjusted during installation to help balance the system and ensure all radiators heat evenly.

• Further reading: What Is A Lockshield Radiator Valve?

9. Lockshield Cap

The lockshield valve is often covered by a protective plastic cap. It’s not meant to be adjusted frequently. Instead, it’s set during installation by a heating engineer to balance water flow across your radiators. Adjusting it incorrectly can cause heating imbalances, so it's usually left alone.

• Further reading: How To Balance A Radiator - A Complete Guide

10. Bleed Valve (Air Vent)

The bleed valve is a small screw or cap located at the top corner of the radiator. Over time, air can get trapped inside the system and stop the radiator from heating properly. Using a radiator key, you can release the trapped air (called “bleeding” the radiator) to restore full heat output.

• Further reading: How To Bleed A Radiator - A Complete Guide

11. Mounting Brackets

These metal brackets are fixed to the wall and hold the radiator securely in place. They support the radiator’s weight and ensure there’s enough space behind for air to circulate and for maintenance access.

• Further reading: How To Fit A Vertical Radiator

12. Flow Pipe

This pipe brings hot water from the boiler to the radiator. It connects to the inlet valve and is usually located at the bottom of the radiator. The water flows in, travels through the internal channels, and heats the radiator body.

• Further reading: How To Pipe A Radiator Video

13. Return Pipe

The return pipe carries cooler water back to the boiler after it’s passed through the radiator. It connects to the outlet valve and completes the circuit in your central heating system, ready for the water to be reheated and recirculated.

• Further reading: A Quick & Easy Guide to Central Heating Inhibitor

Understanding how it all works together

When your heating comes on, hot water is pumped from your boiler through the flow pipe into each radiator’s inlet valve. The water fills the radiator, warming the panels and convector fins, which then heat your room through both radiation and convection. As the water cools, it exits through the return pipe and heads back to the boiler to be reheated.

Your radiator valves, air vent, and pipework all help control and maintain this process, ensuring efficient heating and even temperature throughout your home.

Radiators might seem simple on the outside, but each part plays a key role in keeping your home warm and comfortable. Understanding the basic components can help you troubleshoot problems, bleed a radiator when needed, or simply feel more confident when upgrading your heating system.

If you're looking for new radiators or valves to suit your space, check out the full range at Trade Radiators – with styles to suit every room and budget.