Isolation Valves and Service Valves: Which to Use and Where

An isolation valve is one of the most-fitted items in any plumber's bag — and one of the most frequently confused. Flat-faced, angle, full bore, service valve, gate valve: the names blur together on a counter, but the differences matter when you're under a sink matching a valve to the actual pipework and application. This guide covers every type in the Embrass Peerless range at APM, when to use each, and the two things that most commonly cause callbacks.

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What an Isolation Valve Actually Does

An isolation valve allows a single appliance or branch of pipework to be shut off without turning off the water to the whole building. Fitted on the cold feed to a basin tap, toilet cistern, washing machine, or boiler, it means a tap washer change or appliance swap doesn't require a trip to the stopcock.

In practice, every tap, toilet, dishwasher, washing machine, and any other appliance connected to water should have an isolating valve on its supply. Water Regulations require that any appliance requiring maintenance must be isolatable without disrupting the rest of the system.

Types of Isolation Valve: Flat-Faced vs Angle vs Full Bore

Check the Connection and Sealing Face

Match the actual pipe and hose connections to the selected valve. A compression-to-threaded tap connection is different from an inline compression-to-compression valve. Use the manufacturer’s product information to confirm the connection, sealing arrangement and operation rather than treating every valve as interchangeable.

• Embrass Peerless Flat-Faced Isolating Valve 15mm × ½" — the standard under-tap isolation for 15mm copper to ½" BSP tap tail. The everyday fitted item.
• Embrass Peerless Flat-Faced Isolating Valve 15mm × 3/8" — for fittings with a 3/8" BSP connection (common on older lever taps and some continental fittings).
• Embrass Peerless Chrome Isolating Valve 15mm — inline 15mm compression-to-compression for mid-run isolation where no BSP connection is needed.
• Embrass Peerless Chrome Isolating Valve 22mm — 22mm version for larger supplies: washing machine inlets, dishwasher inlets, or isolating a full branch.

Angle Isolating Valve

The angle valve turns the flow 90° as well as isolating it. Used where the pipe runs along the wall or floor and the tap tail comes straight down — the angle valve connects the two directions in one fitting, saving a separate elbow. Common under kitchen sinks and bathroom vanity units with bottom-entry taps.

• Embrass Peerless Angle Isolation Valve CP 15mm — 15mm compression inlet, ½" BSP outlet. The angle valve that goes under the vast majority of kitchen and bathroom taps.
• Embrass Peerless Angled Service Valve 15mm × ½" — a simpler service valve (no screwdriver slot, uses a flat-blade to operate the internal spindle) for situations where the valve will rarely be touched. Lighter duty and cheaper — used on cistern feeds, appliance inlets.

Full Bore Isolating Valve

Standard isolating valves have a reduced bore internally — the waterway through the valve is smaller than the pipe bore. This creates a small pressure drop. For high-flow applications (main supply, shower feeds, combi boiler cold mains inlet) a full bore valve maintains flow rate through the fitting.

• Embrass Peerless Full Bore Isolating Valve 15mm — full bore design for applications where pressure drop matters. Use on shower supplies, high-pressure combination boiler inlets, and anywhere you're already dealing with marginal pressure.

Tee Isolating Valve

The tee iso valve is a three-way fitting: it splits the supply into two outlets, with an integrated isolating valve on one branch. Common for fitting a washing machine or dishwasher cold supply off an existing 15mm run without adding a separate tee and valve. One fitting does the job of two.

• Primaflow 15mm Tee Isolating Valve CxC

Gate Valves and Replacement Selection

Gate valves are encountered in water installations, including maintenance work. Select a replacement using the manufacturer’s pressure, temperature, connection and application data rather than assuming every installation needs one valve type.

• View the 15mm gate valve listing
• View the 22mm gate valve listing

Backflow Protection: Match the Risk Category

A double-check valve protects only the applications and risk level for which it is rated. Water Regs UK explains that hoses used solely for a domestic garden or washing a personal vehicle are typically fluid category 3; the required protection depends on the actual use.

Bidet showers and douches adjacent to toilets are fluid category 5 risks. A double-check valve alone does not provide the required protection. Both the cold supply and, where applicable, hot supply need a suitable fluid category 5 backflow arrangement, such as a break tank with a Type AB air gap. Confirm the design and notification requirements with the local water undertaker and a qualified installer. Read Water Regs UK’s bidet/douche guidance.

View the 15mm DZR double-check valve for applications where that device is suitable; this is not a bidet/douche compliance kit.

The Two Most Common Isolation Valve Callbacks

1. A seized or damaged valve

Follow the valve manufacturer’s maintenance and operating instructions. If a valve is seized or damaged, do not force the control; have a qualified plumber assess the repair and how to isolate the supply safely.

2. Wrong valve for the pressure

Select the exact valve using the manufacturer’s stated working pressure, temperature limits, connection and intended application. Check the required flow as well. Do not infer pressure suitability from “standard” or “full bore” wording alone; ask APM or the manufacturer if the model’s rating is unclear.

Summary: Which Valve for Which Application

Check current product availability before ordering. Choose collection at checkout where offered and wait for the ready-to-collect confirmation. Contact the Acton team with your valve model, connection sizes and quantities for help finding a match.

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