Polytank feed and expansion tank (4 gallon/18 litre)

The Polytank feed and expansion tank is a feed and expansion tank produced by Polytank Group Ltd, the British manufacturer of water tanks and cisterns. As the name implies, the tank is designed to be used as a feed and expansion tank for open-vented central heating systems. It is suitable for new properties or as a replacement header tank on an existing installation. It has a capacity of 4 gallons / 18 litres.

Polytank feed and expansion tank

The tank is supplied with a snap-on lid, ensuring that dirt, insects and rodents cannot get inside, and a screened warning pipe fitting and washer, which also protects dirt and debris from entering the cistern via the overflow pipe.

You’ll also find a 15 mm Part 2 ball valve and a plastic float, and also a float valve backing plate – a small piece of plastic fitted to the ball valve shank, which protects the tank wall from the upward force of the float.

There’s also a insulation jacket for preventing heat loss, and a length of string for tying the insulation jacket around the tank. A service valve which would allow you to isolate the ball valve with a screw driver is unfortunately not included, however this can easily be purchased separately for a couple of pounds.

The tank is factory sealed, and all of the fittings are to be found inside the tank itself.

Note that while the capacity of the tank is listed as 4 gallons / 18 litres, the feed and expansion tank should never be full to this capacity when cold. The water level should be only slightly higher than the outlet at the bottom of the tank. This is so that the water in the central heating system has room to expand.


The Polytank 4 gallon/18 litre feed and expansion tank is WRAS approved, and is manufactured to BS4213:2004 and in ISO 9001:2008 approved factories.


Length: 480 mm
Width: 250 mm
Height: 320 mm
Weight: 2.2 kg

Where to buy

The Polytank 4 gallon/18 litre feed and expansion tank is available B&Q, which offers free delivery on orders over £50 and a click-and-collect service.