The Tower ABBV1 is a 22mm angled automatic differential bypass valve for sealed central heating systems, designed to maintain a minimum flow rate through the boiler whenever thermostatic radiator valves (TRVs) or zone valves close down. Installed in a loop between the heating flow and return, the ABBV1 opens automatically when system differential pressure rises to the set point — routing water through the bypass and preventing the pump from circulating against a closed or near-closed circuit. The adjustment dial sets the opening pressure from 0.1 to 0.6 bar and locks in place with a screw, giving the installer precise control matched to the system's pump curve. Maximum flow capacity is 50 litres per minute, suitable for the full range of domestic sealed heating systems.

22mm

Compression — angled

0.1–0.6 bar

Adjustable & lockable

50 L/min

Max flow capacity

Automatic

No electrical connection

ℹ Installation Position
Fit the ABBV1 in a loop between the flow and return pipework, after the pump. Flow must enter in the direction of the arrow marked on the valve body. For most domestic installations the valve is sited adjacent to the boiler or in the airing cupboard, bridging between two parallel 22mm pipework runs. The angled configuration (90° ports) means no additional bends are needed where the flow and return run parallel and close together.

Features & Benefits

✔ Adjustable 0.1–0.6 Bar — Lockable Dial

A visual numbered dial adjusts the bypass opening differential pressure from 0.1 to 0.6 bar. Once set, a screw on top of the adjuster locks the position — preventing accidental drift after commissioning. A setting of 0.2–0.3 bar suits most domestic systems; the correct value should match the boiler manufacturer's minimum flow requirement and the system's pump curve. The wider 0.6 bar upper range makes the ABBV1 suitable for higher-head pump systems where a standard bypass valve would open prematurely.

✔ Protects the Boiler Heat Exchanger

Modern condensing boilers — especially those with compact plate heat exchangers — require a minimum flow rate at all times, regardless of how many radiators are calling. When TRVs close down as rooms reach temperature, flow restriction rises sharply. The ABBV1 opens to divert enough flow to satisfy this minimum requirement, preventing localised overheating, kettling, and the premature PRV trips that result from high static pressure in a closed circuit.

✔ Protects the Pump — Eliminates Noise

A pump running against a closed head creates high differential pressure, causes impeller wear, and generates pipe noise — the familiar banging or high-pitched hum when TRVs close. The ABBV1 opens progressively as pressure builds, maintaining a stable system pressure and eliminating the pressure spikes that propagate as noise through pipework. Pump life is extended by avoiding the closed-head condition entirely.

✔ 50 L/min — High Capacity for Any Domestic System

With a maximum flow capacity of 50 litres per minute, the ABBV1 handles the bypass demand of any standard domestic sealed heating system, including those with high-output boilers or multiple zone valves. This capacity significantly exceeds simpler spring-loaded bypass valves, ensuring the bypass can carry adequate flow even when several zones close simultaneously.

✔ 22mm Compression — No Soldering

Standard 22mm compression fittings allow installation on existing copper pipework without a blowtorch — suitable for retrofit on occupied premises, gas-purged areas, or anywhere open flame is not permitted. The compression joints can be remade without cutting the pipework, simplifying future access or replacement.

✔ Pump Overrun Support

Many boiler controllers run the pump for a short overrun period after the burner shuts off — to extract residual heat from the heat exchanger. During this overrun, if zone valves have already closed, the pump has no circuit to circulate through. The ABBV1 provides the bypass path needed for pump overrun to complete correctly, preventing the pressure lockouts that can occur when a pump overruns into a sealed-off system.

Technical Specifications

Manufacturer / Part No.	Tower (TFC Group) — ABBV1
Configuration	Angled (90° inlet/outlet)
Connection Size	22mm compression
Differential Pressure Range	0.1 – 0.6 bar (adjustable and lockable)
Max Flow Capacity	50 litres/minute
Operation	Automatic differential pressure — no electrical connection required
Setting	Visual numbered dial — lockable via screw on adjuster
Applications	Sealed CH systems with TRVs; boiler bypass; zone valve systems; pump overrun protection

Plumbing Valves