Radiator Valves: Angled, Straight, and Corner — A Trade Guide to Selection, Connection, and Balancing

Radiator valves are among the most frequently replaced components in domestic and commercial heating systems. Every radiator has two — a control valve on the flow side and a lockshield on the return — and choosing the right type depends on pipework configuration, pipe centres, microbore vs standard bore, and whether the customer wants manual or thermostatic control. This guide covers everything a heating engineer needs to know: valve geometry, connection types, pipe centre specifications, DZR brass requirements, and how radiator valves fit into system balancing.

Why Radiator Valve Selection Matters

Fitting the wrong valve geometry wastes time and money: a straight valve on a floor-piped installation requires costly pipe modifications, while fitting a corner valve to a wall-piped system creates an untidy installation. Beyond geometry, valve quality affects long-term performance — cheap valves use poor packing glands that weep within a few years, and undersized valves restrict flow on high-output radiators. Specifying correctly from the outset is good practice and protects your reputation.

Valve Geometry: Straight, Angled, and Corner

Straight Valves

Straight radiator valves connect inlet and outlet in a straight line — the pipe comes horizontally from the wall and connects directly into the valve body, which then connects vertically up into the radiator tail. They are used where pipes run horizontally along the skirting or emerge from the wall at the same level as the radiator inlet. Common in older properties and in systems where the pipework was designed around straight valve geometry.

Standard straight valve bodies are available in 15mm (the most common UK domestic size) and in 10mm for microbore systems. The valve-to-radiator connection is via a ½" BSP (British Standard Pipe) taper thread into the radiator tail, using a union nut and olive (compression) or a push-fit union.

Angled Valves

Angled valves — also called angle valves or elbow valves — turn the flow through 90°: the pipe enters from below (rising through the floor) and the valve body turns it 90° to connect horizontally into the radiator tail. This is the most commonly specified valve geometry in modern UK domestic installations, where plastic plumbing pipes (JG Speedfit, Hep2O) rise from the floor and connect at the base of the radiator.

Angled valves are available in 15mm compression, 15mm push-fit, and 10mm microbore versions. The vertical pipe entry makes them compatible with underfloor pipe routes and suspended timber floors with pipes running in the joist space.

Corner Valves

Corner valves (also called T-piece or double-elbow valves) turn through two planes — the pipe enters from one direction and the valve connects in a perpendicular plane at 90° both horizontally and vertically. They are used where pipework runs along the skirting board and needs to turn the corner at the base of a radiator without visible pipe bends. Less common than straight or angled, but useful for awkward radiator positions or where pipework needs to change direction at the valve.

Identifying the Right Geometry

• Pipes from floor, radiator against wall: Angled valve
• Pipes from wall, horizontal, at radiator height: Straight valve
• Pipes from skirting, needing a turn at the radiator base: Corner valve
• Hidden in-wall pipework (e.g., flat-to-wall radiator): In-wall concealed valve bodies (Pegler, Giacomini)

Pipe Centre Spacing

UK radiators are manufactured with standard pipe centres — the horizontal distance between the flow and return tails at the bottom. The two standard spacings are:

• 50mm pipe centres: Modern UK standard. Panel radiators (Stelrad, Myson, Quinn) all use 50mm centres. This is what you'll find on any new installation.
• 100mm pipe centres: Older UK standard, still found on some column radiators, school radiators, and cast iron replacements.

Radiator valve sets are sold as pairs and specify compatibility with 50mm or 100mm centres. On modern 50mm centre radiators, angled valve sets are the default. When replacing radiators in older properties with 100mm centres, check valve compatibility or adjust pipework.

Column radiators often have different tail configurations — some columns have side tails, some have bottom entries — so always check the radiator specification sheet before ordering valves.

Radiator Tails and Adaptors

The radiator itself has ½" BSP female ports. The radiator tail (a short brass nipple) threads into the port and provides the male ½" BSP taper connection for the valve union. On most panel radiators, tails come pre-fitted or are supplied in the box.

Blanking plugs (½" BSP male) seal unused ports — a standard panel radiator has four ports (top left, top right, bottom left, bottom right). The two unused ports opposite the valve positions are blanked. One port on the top may take a manual air bleed valve (Schrader-type or slotted square).

Radiator tail sizes: Most UK valves use ½" BSP at the radiator connection. Some older or European radiators use ¾" BSP — use a ¾" to ½" BSP reducer tail in this case. Never force an incompatible size.

Valve Head Types

Wheelhead (Manual) Valves

Manual radiator valves use a hand-turned wheelhead to open and close the valve. They provide full flow control (fully open to fully closed) and are typically used on the flow side where the occupant wants manual on/off or partial flow adjustment. Wheelhead valves are less common as primary controls in modern installations — TRVs have largely replaced them — but remain appropriate where:

• The radiator is in the same room as a room thermostat (TRVs should not be fitted in the same room as the room stat)
• The room temperature is controlled by other means (e.g., electric UFH thermostat, smart controller)
• A simple backup or override is required

Thermostatic Radiator Valves (TRVs)

TRVs use a wax-filled or liquid-filled sensor head to modulate flow based on room temperature. When the room reaches setpoint, the wax expands and closes the valve; as the room cools, it contracts and the valve reopens. Modern TRVs are available in liquid-sensing (more responsive) and wax-sensing types.

TRV heads are typically interchangeable across compatible valve bodies — the head connects via a union nut and the valve body is the same as a manual valve. This means a wheelhead valve body can be upgraded to TRV by fitting a TRV head. Common head connection sizes: M30 × 1.5mm thread is near-universal for UK/European TRVs. Always verify compatibility before fitting a different brand head to a valve body.

For a detailed guide to TRV types, draught-proof settings, and positioning requirements, see our article on Thermostatic Radiator Valves.

Lockshield Valves

The lockshield goes on the return side of the radiator. It has a removable plastic cap that, when removed, reveals a valve spindle that can be adjusted with a flat-blade screwdriver or a special lockshield key. Once set to the correct position during balancing, the cap is replaced to prevent tampering.

During radiator balancing, the lockshield is adjusted to restrict flow through radiators that heat up too quickly (typically those closest to the boiler). This ensures even heat distribution across the circuit. The degree of opening (number of turns from fully closed) is recorded and can be referred to when the system is drained and refilled.

Standard lockshield valves have a lockable cap and are sold as the paired return-side complement to wheelhead or TRV valves in radiator valve packs.

Drain-Off Valves

Some lockshield valves incorporate a drain-off point — a small ⅛" BSP tapping fitted with a drain cock. This allows the individual radiator circuit to be drained without draining the entire system, which is useful when replacing a single radiator. When fitting radiator valve packs, consider whether drain-off capability is required.

Connection Types: Compression vs Push-Fit

Compression Radiator Valves

Compression valves grip the copper pipe using an olive and union nut. The pipe is inserted into the valve body, the olive seats on the pipe, and tightening the union nut (typically 1¼ turns past hand-tight for 15mm) compresses the olive to create a leak-free joint. Compression is the traditional and still most common method:

• Compatible with copper pipe (most common) and chrome-plated copper tails
• Demountable — the joint can be remade if the valve is replaced
• DZR brass body required where chlorine levels are elevated or where WRAS compliance is needed (see below)

Push-Fit Radiator Valves

Push-fit radiator valves (from JG Speedfit, Hep2O/Wavin, and others) accept plastic barrier pipe or copper pipe and grip via internal collets. They are faster to install than compression — no tools required — and are particularly common in new-build installations where plastic pipework runs from the manifold to each radiator. Key considerations:

• Always use the correct insert (pipe stiffener/liner) in plastic pipe before pushing into a push-fit valve
• Pipe must be cut cleanly and squarely — a ragged cut will prevent the collet from seating correctly
• Some push-fit valves are demountable; others are single-use — verify before specifying
• For Hep2O barrier pipe, use Hep2O push-fit valves or JG Speedfit valves rated for barrier pipe

For a detailed comparison of push-fit systems, see our guide to Push-Fit Plumbing: JG Speedfit and Hep2O.

Microbore Radiator Valves (8mm and 10mm)

Microbore heating systems use 8mm or 10mm copper tube run from a central manifold to each radiator. They were popular in the 1970s and 1980s and are still found in many properties. Microbore radiator valves are smaller than standard 15mm valves and connect directly to 8mm or 10mm pipe using compression olives.

Key differences vs standard 15mm systems:

• Microbore valves have smaller flow areas — they restrict flow more than 15mm valves, which is fine for a single radiator but limits how far from the manifold a run can go
• 8mm pipe is prone to blockage from magnetite sludge — systems with microbore pipework benefit significantly from magnetic filter fitting and annual filter cleaning
• When replacing a manifold system with modern plastic pipe, 10mm plastic barrier pipe (JG Speedfit, Hep2O) is the standard upgrade path

DZR Brass: When and Why

Dezincification-resistant (DZR) brass is required for valve bodies in areas with aggressive water supplies — particularly where chlorine levels are elevated or where WRAS approval is needed for drinking water compliance. Standard yellow brass (CW617N) can dezincify in aggressive water, leaving a porous, weakened copper structure that eventually fails.

DZR brass (typically CW602N or marked DZR or CR) resists dezincification through a small addition of arsenic. UK Water Regulations require DZR brass for fittings in contact with potable water where aggressive water conditions are present. For heating systems (closed circuits with inhibitor), dezincification risk is lower, but specifying DZR valves adds minimal cost and provides peace of mind.

WRAS-approved radiator valves carry the Water Regulations Advisory Scheme mark, indicating they have been tested and approved for use in UK water systems. Always specify WRAS-approved valves on any potable water-touching components.

Radiator Valve Packs

Radiator valve packs — sold as matched pairs — include the TRV (or wheelhead) for the flow side and the lockshield for the return side, plus union nuts, olives, and radiator tail fittings. Most packs also include a blanking plug for unused radiator ports and a manual air bleed valve.

Common pack configurations:

• Angled TRV + angled lockshield — standard new-build domestic pack, 15mm compression
• Straight TRV + straight lockshield — for wall-piped installations
• Angled wheelhead + angled lockshield — for rooms with room stats or where TRVs are not required
• Angled TRV + straight lockshield — where the flow and return pipes approach from different directions

When ordering valve packs, specify: geometry (angled/straight/corner), connection size (15mm or 10mm), and head type (TRV or manual). Many brands (Drayton, Pegler, IMI Heimeier, Reliance Water Controls) supply compatible head-to-body combinations.

Valve Bodies and Interchangeable Heads

Many European radiator valve systems use a standardised M30 × 1.5mm thread on the valve body, allowing TRV heads from different manufacturers to be fitted to the same valve body. This is useful for upgrading a legacy system with new TRV heads (e.g., adding a smart TRV head to an existing Pegler valve body) without replacing the full valve.

Common UK head-body compatibility notes:

• Drayton TRV4 / TRV+4: Uses Drayton's own proprietary connection — not M30 compatible without adaptor
• Pegler Yorkshire: M30 × 1.5mm — compatible with most Danfoss, Honeywell, and generic heads
• IMI Heimeier: M30 × 1.5mm — widely compatible
• Heatmiser, Tado, Nest TRV heads: Typically supplied with M30 adaptor and a range of adaptors for proprietary valve bodies

Always check the smart TRV head manufacturer's compatibility list before specifying for an existing system.

Chrome and Designer Valves

Chrome-plated radiator valves are standard in UK bathrooms and kitchens where aesthetics matter. Chrome bodies are typically brass with a polished or brushed chrome finish over the nickel base coat. Consider:

• Chrome finishes can show water staining in hard water areas — white vinegar on a cloth removes light scale without damaging the finish
• Never use abrasive cleaners on chrome radiator valves — they scratch the plating
• Antique brass, gun metal, and matte black finishes are increasingly specified in bathrooms — premium finish valves (by Hudson Reed, JTP, Crosswater) use solid brass bodies and are significantly more durable than plated zinc die-cast alternatives

For feature column radiators and designer towel rails, matched valve sets (both angled) in the same finish are typically specified by the installer. See our guide to Heated Towel Rails for valve selection on dual-fuel and electric towel rails.

Installation: Step-by-Step

1. Isolate and Drain

Close both radiator valves (if existing) and drain the radiator using a radiator drain key. If no drain valve is fitted, the system may need to be partially drained — close the relevant zone valve or turn off the pump and use the lowest drain-off point on the circuit. Before draining, add a bucket below the valve being removed.

2. Remove Old Valves

Use a pipe wrench and a second spanner to hold the radiator tail while undoing the union nut. Avoid twisting the radiator tail — if it turns in the radiator port, the radiator body seal may fail. Once the union nut is clear, pull the valve off the pipe. Note the olive position on the pipe and whether it's distorted — if so, cut the pipe back 5–10mm to expose fresh copper before fitting the new valve.

3. Check Pipe Squareness

Ensure the pipe end is cut cleanly and square. Use a pipe slice (rotary pipe cutter) rather than a hacksaw — it produces a cleaner, squarer cut with minimal burr. Deburr and clean the pipe end with wire wool or emery cloth.

4. Fit New Valve

Slide the union nut onto the pipe (thread-first), then the olive. Push the valve body onto the pipe, ensuring the pipe is fully home (to the stop inside the valve body on push-fit, or to the correct insertion depth on compression). Hand-tighten the union nut, then tighten ¼ to 1¼ turns with a spanner (compression) or to the manufacturer's instruction (push-fit).

Apply PTFE tape or Loctite 55 thread sealant to the ½" BSP tail threads before screwing into the radiator tail. Tighten firmly — 1½ to 2 turns past hand-tight — but do not overtighten as this can crack the radiator header.

5. Fit Lockshield on Return

Repeat for the lockshield valve on the return side. Open the lockshield two full turns initially (to be adjusted during balancing).

6. Refill and Test

Refill the system via the filling loop, vent the radiator using the bleed valve, and check for leaks at both valve unions. Open the TRV fully, restore power to the pump and boiler, and allow the system to circulate before checking temperatures and balancing.

Balancing Radiator Valves

Balancing ensures even heat distribution across all radiators. In an unbalanced system, radiators closest to the boiler (lowest resistance) overheat while distant radiators fail to reach temperature. The lockshield valve on each radiator is used to restrict flow to the fast-heating radiators, evening out ΔT (flow-to-return temperature difference) across the circuit. Target ΔT is typically 10–12°C across each radiator for LTHW (low temperature hot water) systems.

For the full balancing procedure including lockshield turns, Delta T measurement, and flow temperature optimisation, see our guides on Radiator Balancing and Heating System Balancing.

Common Problems with Radiator Valves

Weeping Packing Gland

A drip from around the valve spindle indicates a failed packing gland. On some valves, the packing can be replaced by removing the head and tightening or replacing the packing nut. On cheaper valves, replacement of the entire valve is more practical. PTFE tape wound around the spindle is a temporary fix but not a permanent solution — replace the valve at the next service visit.

TRV Head Not Closing

A TRV that stays open (radiator always hot regardless of head position) usually means the valve pin is stuck — typically due to scale or corrosion on the valve pin. Remove the TRV head and manually press the valve pin with your finger — it should depress about 2–3mm. If stuck, apply a small amount of penetrating oil around the pin base and work it loose. If the pin cannot be freed, replace the valve body.

Valve Pin Stuck Closed

In a house left empty over winter with the heating off, TRV valve pins can seize in the closed position — the wax element pushes the pin down and corrosion holds it there. The radiator will be completely cold. Fix: remove the TRV head, press and release the pin repeatedly with your finger. If seized beyond manual release, the valve body requires replacement.

Noisy Valve (Hammering or Hissing)

Hissing from a TRV at low flow settings indicates cavitation — water flashing to steam as it passes through a restricted orifice. This can be caused by excessive system pressure or a TRV nearly closed with high differential pressure across it. Fitting a pressure-independent control valve (PICV) or adding automatic bypass capacity reduces this effect. See our guide on Central Heating Bypass Valves for managing differential pressure in modulating systems.

Union Nut Dripping

A drip at the compression joint (union nut) indicates an under-compressed olive or a distorted olive from previous over-tightening. Tighten ¼ turn and monitor. If the drip persists, drain and refit with a new olive — never repeatedly overtighten, as this damages the valve body threads.

Valve Selection Summary

Stocking Recommendations for Heating Engineers

A well-stocked van for radiator valve work should include:

• Angled TRV valve packs (15mm compression) × 4–6
• Angled wheelhead + lockshield packs (15mm compression) × 2
• Straight TRV valve packs (15mm compression) × 2
• 10mm angled TRV valve packs × 2 (for microbore)
• Chrome versions of the above for bathroom/kitchen work
• Spare radiator tails (½" BSP) × 4
• Spare 15mm olives × 10–20
• Blanking plugs (½" BSP) × 6
• Manual air bleed valves × 6
• Lockshield keys (spare)
• 15mm pipe slice and deburring tool
• PTFE tape and Loctite 55

Related Guides

• Thermostatic Radiator Valves (TRVs): Types, Settings, and Installation
• Radiator Sizing: BTU Calculation and Panel Type Guide
• How to Balance a Central Heating System: Radiator Balancing Step by Step
• Heating System Balancing: Flow Temperatures and Lockshield Setting
• Central Heating Bypass: Automatic Bypass Valves and Differential Pressure
• Push-Fit Plumbing: JG Speedfit and Hep2O Installation Guide
• Magnetic Filters for Central Heating: MagnaClean, Fernox TF1, and Sentinel
• Heated Towel Rails: Electric, Dual Fuel, and Central Heating Trade Guide
• Central Heating Inhibitor and System Flushing