Radiator Valves — Angled, Straight, TRVs and Lockshield for UK Heating Engineers

Every radiator in a UK central heating system needs a valve at each end — one to control heat output and one to balance the circuit. Getting the right combination of radiator valves matters for comfort, efficiency, and compliance with Part L of the Building Regulations. This guide covers the types of radiator valve stocked by APM, how to choose between angled and straight fittings, and when thermostatic radiator valves (TRVs) are required.

Types of Radiator Valve

There are three main valve types used in domestic and light commercial heating systems:

• Manual (wheelhead) valves — the traditional on/off type. Turn fully open or to a fixed position. Lower cost, no moving parts to fail, and suitable where the room temperature is controlled by a room thermostat instead.
• Thermostatic radiator valves (TRVs) — contain a wax or liquid element that expands and contracts with air temperature, automatically reducing flow as the room warms up. Required on new and replacement radiators under Part L of the Building Regulations (England and Wales) in most circumstances.
• Lockshield valves — fitted on the return side of every radiator. Used during system balancing to restrict flow and ensure even heat distribution around the circuit. Adjusted once at commissioning and normally left set. Usually supplied as a pair with a TRV.

Angled vs Straight: Which Do You Need?

The fitting direction is determined by where the pipework enters the radiator:

• Angled valves are by far the most common in UK homes. Pipes rise vertically from the floor (underfloor pipework) and turn 90° to enter the radiator at the side. Angled valves make this turn neatly against a skirting board.
• Straight valves are used where pipes come horizontally out of the wall and connect directly into the radiator side inlet at the same height. More typical in older properties with surface-run pipework or in bathrooms with towel rails.
• Corner valves connect pipes that run along the floor and turn the corner to come up close to the wall — used where a radiator sits in a corner with limited clearance.

Some valves are described as reversible — the same body can be installed with either an angled or straight pipe connection, which simplifies stock management for heating engineers carrying only one valve type.

Pipe and Connection Sizes

UK domestic radiators use a standard ½" BSP tail thread on each inlet/outlet. The valve body connects to the copper pipework at the other end — almost always 15mm compression in modern systems. Older systems may use 22mm pipework to the first radiator on a gravity primary circuit, but TRVs for these are less common.

Always confirm: 15mm compression inlet × ½" BSP radiator tail for standard domestic use.

Part L and TRV Requirements

Under Approved Document L (Conservation of Fuel and Power), all new or replacement radiators in existing dwellings must be fitted with TRVs — with the exception of a single radiator in the room containing the main room thermostat (to avoid hunting conflicts). Boiler replacement work must also ensure TRVs are fitted across the system where they are absent.

Heating engineers should carry a mix of angled TRV packs (the most common requirement) and individual lockshield valves for system balancing top-ups.

Balancing the System

Fitting a TRV controls individual room temperature, but system balancing via the lockshield valve is still essential. On a poorly balanced system, radiators near the boiler receive too much flow and run too hot, while those at the far end of the circuit remain cool. Partially closing the lockshield on nearer radiators and opening those further away achieves even delta-T across the system — typically 10–12°C on a modern condensing boiler running flow temperatures of 55–70°C.

APM Radiator Valves

Embrass Peerless 15mm Radiator Valve Reversible Angled 1/2″ Nut

The go-to manual angled valve for domestic radiator installations. Reversible body fits pipe from floor or wall without needing a separate angled variant. 15mm compression inlet, ½″ BSP radiator tail connection. Chrome-plated brass body.

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Embrass Peerless 15mm Radiator Valve Reversible Straight 1/2″ Nut

Straight manual radiator valve for horizontal pipework connections — typically used on wall-mounted pipes, panel radiators in bathrooms, or towel rail installations. Same reversible body as the angled version. 15mm compression × ½″ BSP.

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EDEN 15mm Straight Thermostatic Radiator Valve — White

Affordable thermostatic radiator valve for Part L compliance on straight-pipe connections. White head and body suits modern panel radiators. Self-limiting wax element closes as room temperature rises. 15mm compression inlet. Lockshield sold separately or in the angled pack below.

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EDEN Thermostatic Radiator Valve Pack Angled c/w Lockshield 15mm — White

Everything needed to fit a single radiator correctly under Part L. Includes angled TRV for the flow end and matching lockshield for the return. White head and valve body. 15mm compression on both valves. The most efficient way to carry stock for new radiator installations and boiler replacement work.

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Fitting Tips for Heating Engineers

• Teflon tape vs fibre washer — TRV bodies typically use a copper or fibre washer on the radiator tail connection. The compression end uses olive and nut — no tape needed.
• TRV orientation — most modern TRVs can be mounted horizontally or vertically. Avoid mounting with the head pointing down (condensation can affect the sensing element on liquid-filled types). Angle the head away from heat sources where possible.
• Remote heads — if a TRV would be blocked by curtains or furniture (common with underfloor pipework and low-level radiators), use a remote-head TRV or a programmable head to ensure accurate sensing.
• Drain down before fitting — always inhibit the system after drain-down and refill. Mains water without inhibitor in a sealed system causes rapid corrosion and magnetite build-up. Fernox F1 or equivalent at the correct dose per system volume is standard practice.
• Lock setting on lockshield — after balancing, count and note the number of turns on each lockshield. This allows quick restoration after any drain-down without a full rebalance.

Manual vs TRV: Making the Right Choice

Order Radiator Valves from APM

APM Electricals stocks a full range of radiator valves for domestic heating engineers — angled and straight manual valves, TRVs with and without lockshield packs, and corner fittings for awkward radiator positions. All 15mm compression fittings. Available for click-and-collect from our Acton trade counter or for delivery.

APM Electricals — Electrical and Plumbing Trade Supplies
24 Western Avenue, Acton, London W3 7TZ
Tel: 020 8702 8080
Same-day collection available. Trade accounts welcome. www.apmi.uk