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July 18, 2026 APM Electricals

Plumbing Valves: The Complete Guide to Radiator Valves, Ball Valves, Gate Valves, Stopcocks and Isolators

Plumbing Valves: The Complete Guide to Radiator Valves, Ball Valves, Gate Valves, Stopcocks and Isolators

Valves control, isolate, regulate, and direct water flow throughout a plumbing installation. Choosing the wrong type — a gate valve where a ball valve is needed, or a standard radiator valve where a TRV is required — creates problems that are expensive to rectify once the system is live. This guide covers every valve type in the Embrass Peerless range stocked at APM, with guidance on where each type is used and why.

Radiator Valves — Manual and Thermostatic

Every radiator requires two valves: a flow valve (which regulates or shuts off the water entering the radiator) and a lockshield valve (which balances the circuit and provides isolation for maintenance). For new domestic heating installations under current Building Regulations Part L, thermostatic radiator valves (TRVs) are required on all radiators except one — which must be in the same room as the room thermostat.

EDEN Thermostatic Radiator Valves (TRVs)

TRVs have a thermostatic head that responds to room temperature: as the room warms, the valve closes; as it cools, it opens. This gives room-by-room temperature control without additional wiring. All EDEN TRVs fit standard 15mm radiator tails with ½" or ¾" union nuts.

Manual Radiator Valves (Flow Valves)

Where a TRV is not specified — radiator in the thermostat room, bathroom towel rails, electric heating — a manual radiator valve provides simple on/off isolation with a handwheel.

Towel Rail / Derwent Radiator Valve

Isolating Valves — Under Taps and Appliances

Isolating valves are fitted on the supply pipes to taps, toilets, dishwashers, and washing machines to allow individual appliances to be turned off and serviced without draining the system. The slot-head quarter-turn design requires a flathead screwdriver to operate — not hand-operable — which prevents accidental operation.

Lever Ball Valves — Full Isolation and Zone Separation

Lever ball valves provide full-bore isolation with a quarter-turn handle — quicker to operate and easier to confirm open/closed status than screwdriver-slot isolators. Used for zone isolation on heating circuits, boiler service valves, and any point where a full-bore, hand-operable shutoff is needed. The lever position makes the valve state immediately visible.

Blue handle = cold water and general plumbing applications. Red handle = hot water and heating circuits. WRAS-approved versions required for potable water supplies.

Compression end (15mm–54mm)

Female BSP threaded (¼ turn, full bore)

Butterfly handle / compact

Press-fit (Pegasus)

Gate Valves — Full Bore, Low Resistance

Gate valves use a wedge-shaped gate that rises fully out of the flow path when open, giving zero flow restriction. They are slow to operate (multiple turns) but ideal for applications where the valve is normally open and the pressure drop across it must be minimal — pump suction lines, zone isolation on gravity heating systems, and CWSC ball valve bypass lines. Gate valves must be either fully open or fully closed; partially throttled, the gate vibrates and wears.

Embrass Peerless Stopcock Brass 22mm

Check Valves (Non-Return Valves)

Check valves prevent reverse flow — critical on hot water cylinders to prevent cold back-siphonage, on boiler primary circuits where pump failure could cause gravity circulation in the wrong direction, and on combination boiler filling loops. DZR (dezincification-resistant) brass is required for hot water and heating applications.

Stopcocks — Mains and Service Isolation

Stopcocks are the standard valve for mains water service entries. Clockwise to close. Unlike a gate valve, the stopcock has a washer-and-seat mechanism that can be reground or re-washered in-situ without removing the body from the pipework — essential for service isolation valves that may not be operated for years.

MDPE Stopcocks — Underground Mains

For terminating MDPE supply pipe at entry to the building, the MDPE stopcock transitions from polyethylene to copper in a single fitting.

Zone Valves and Gas Valves

Motorised Zone Valve

  • Embrass Peerless 22mm 2-Way Motorised Zone Valve — electrically actuated, for use in mid-position 3-port or 2-zone heating controls. Connects to a Honeywell or Drayton zone control wiring centre. Essential for separating heating and hot water circuits where a 3-port valve is not used.

Gas Isolation Valves

Washing Machine Valves

Flexible Tap Connectors with Isolating Valves

Pre-assembled flexible tap connectors with built-in isolating valve save time on kitchen and bathroom tap connections — one fitting provides both the flexible connection to the tap tail and the isolation point.

Boiler Filling Loop

  • Embrass Peerless 15mm Filling Loop Straight — for re-pressurising sealed heating systems. Double check valve built in for Water Regulations compliance. Disconnect and store after use — the filling loop must not remain permanently connected.

The full Embrass Peerless valve range is stocked at APM's Acton trade counter — same-day collection available on all sizes.

APM Plumbing & Electrical | 24 Western Avenue, Acton, London W3 7TZ | 020 8702 8080 | apmi.uk

Filed in: ball valve, check valve, EDEN TRV, Embrass Peerless, gate valve, isolating valve, plumbing valves, radiator valves, stopcock, thermostatic radiator valve, TRV
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