Description
This is a compact, replacement powerhead for 3‑port mid‑position valves used in conventional central‑heating and hot‑water systems. Mechanically it mounts to the common VAL322MP / VAL328MP valve bodies (22mm and 28mm) and electrically it provides the motorised mid‑position action that directs boiler flow to heating, to hot water, or to both together — the behaviour expected in a typical Y‑plan installation.
The unit is a synchronous motor actuator with spring return and an integrated auxiliary (end) switch. It is supplied as a 1‑metre, 5‑core flex and includes a manual override lever so engineers can operate the valve by hand while commissioning, bleeding or draining. It is sold and supported under Tower (TFC Group) as the A3MID code and is widely offered as a like‑for‑like replacement for powerheads fitted to Honeywell V4073A‑style mid‑position valves.
Key specifications
- Supply: 220–240 V AC, 50 Hz
- Motor type: synchronous motor with spring return; power consumption c. 6 W
- Cable: 1 m, 5‑core flex (standard colours: white, grey, orange, blue, green/yellow)
- Auxiliary (end) switch: fitted; switch rating 3 A resistive
- Fits: Tower VAL322MP (22 mm) and VAL328MP (28 mm) valve bodies (mid‑position)
- Weight and size: c. 0.48 kg; dimensions approx. 60 × 85 × 60 mm
How it works on a domestic system
On a mid‑position (3‑port) valve the actuator positions the internal ball or disc so flow from the boiler (port AB) is routed to the heating circuit (port A), the hot‑water circuit (port B), or partially to both when in the mid position. The Tower A3MID provides the motor action to move that element under command from the programmer, room thermostat and cylinder thermostat. The auxiliary switch gives a volt‑free changeover contact that can be used to switch boiler and pump circuits when the valve reaches the required position.
Installation and wiring notes
The A3MID is supplied pre‑wired with a one‑metre 5‑core cable using industry standard colours. For the mid‑position valve the wiring convention used by the manufacturer is: white = room thermostat call (heating on), grey = cylinder thermostat sat (hot water off), orange = cylinder thermostat call (boiler/pump drive for hot water), blue = neutral, green/yellow = earth. The auxiliary switch is built in and the switch contacts are rated at 3 A resistive.
Because it is a direct replacement powerhead, the unit can normally be fitted without removing the valve body or draining the system — follow the advice to put the actuator in the manual‑open position before removal and replacement. All electrical work should be carried out to current regulations by a competent electrician and the system supply should be protected as recommended (the manufacturer references a 3 A supply fuse for the installation circuit). The manual override is useful when filling, bleeding and commissioning but should be returned to the AUTO position for normal automatic control.
Compatibility, practical limits and what to check
The A3MID is intended for the Tower VAL322MP / VAL328MP valve bodies and is widely sold as a replacement for several similar mid‑position powerheads (including many V4073A‑type installations). That compatibility covers mechanical fit, shaft coupling and the standard 5‑wire control arrangement, but it is good practice to check the existing valve or powerhead marking before ordering — valves with non‑standard shafts, different mounting plates or bespoke wiring arrangements will not be interchangeable.
Operational limits to bear in mind: the product is intended for fully pumped systems and the valve body differential pressure limits (for example 1 bar differential on the 22 mm valve) and static pressure ratings apply to the valve assembly — check the valve body datasheet if your system runs under high pressure. The actuator itself is designed for domestic and light commercial environments and has modest power draw (about 6 W) and the small auxiliary switch is intended for signalling boiler/pump circuits rather than switching heavy loads directly.
When this unit is a sensible choice
Choose the A3MID if you have an appropriate Tower VAL322MP/VAL328MP mid‑position valve body (or a physically identical V4073A‑type valve) and you want a straightforward, inexpensive replacement powerhead that restores mid‑position control. It’s a practical spare for plumbers and heating engineers because it is lightweight, pre‑wired in the industry standard colours and includes the manual lever and auxiliary switch installers expect.
It is not a wholesale valve replacement — if the valve body itself is leaking, corroded or mechanically worn then fitting a new head will not cure those faults. Likewise, if your controller wiring differs from the standard arrangement or your system relies on larger switching loads than the actuator’s auxiliary contact can carry, you’ll need to plan for appropriate interposing relays or a different product.
Overall, the A3MID is a purpose‑built, no‑frills mid‑position powerhead intended to keep a conventional central‑heating installation operating reliably, restore correct Y‑plan function and let engineers replace a failed actuator quickly without replacing the valve body.
