Feed and Expansion Tanks

Often people ask us for information on cold water tanks and below is a brief description.

Cold water storage tanks are generally situated in the loft. They can be used to supply the hot and cold water taps on the bath. They can also act as a Feed and Expansion tank (F+E) for the heating system. Most of these tanks are fed by a ball valve on mains pressure. 

Byelaw 30 kits are required to prevent dust and insects entering the water supply

All cold water storage tanks should be purchased with a Byelaw 30 kit. This is a lid for the tank, insulation for the tank and an overflow connection that generally has a filter built in.
Problems that occur with water tanks vary. The most common is an inadequately insulated tank freezing in a cold loft and leaking. Others include connection leaks and build up of oxidised water (red slime) In the case of slime in the tank. Disconnect the tank from the mains water supply and scoop out as much water as possible with a jug. Clean out the slime and re-fill.

The ball valve is a very simple means of turning water off automatically when the desired water volume is achieved. They use a water tight ball of air on an arm to rise up with the water level. As the level gets higher the arm pushes on a plastic button which in turn slowly closes a rubber washer. Also the ball valve can fail in a number of ways. The ball can fill up with water and not lift up to shut the valve or in a hard water areas lime scale can prevent the valve from closing at all. Also they can be ‘stuck up’. This is when the ball valve doesn’t open. This can drain your tank completely before you become aware of a problem. Sometimes a tap of the ball valve can fix the problem but it is advised to buy a new one.
How to change a water storage tank for hot and cold water taps:

1.    Turn off the water supply at the main house stop cock (afterwards install an inline valve on the feed pipe to the tank. Next time you will only have to turn off the water storage tank should you need to service it in the future and not the whole house supply)
2.    Empty the water tank. To do this open all taps and wait for them to stop. Go back in the loft and lift one end of the tank to drain any remaining water.
3.    Disconnect the outlet pipe (usually 22mm) and disconnect the overflow pipe.
4.    Remove the old tank.
5.    Position the new tank and connect the outlet pipe.
6. When connecting the inlet pipe it is generally thought to fit a new ball valve. They aren’t expensive.
7.    You might have to cut a new hole for the overflow. When doing this make sure the overflow inlet is at least 3 inches lower than the bottom of the feed outlet.

This is to prevent water running down the feed into the mains water system in the event of overflow. Always make sure that the overflow pipe has an adequate drop to allow water to run away. Terminate the overflow pipe outside the house and in a visible place.
How to change a water storage tank for a heating system (F+E)
Before following steps 1-7 above, turn the heating system off. You will have to drain the system via a drain point. Then follow the above steps. Once the new tank is installed it is advised you tip in a bottle of inhibitor to protect the heating system components.
How to change a ball valve:
When a ball valve goes wrong the usual sign is the overflow pipe outside of the house is running water and the supply valve doesn’t shut properly.
1.    Turn the mains water off or isolate the ball valve at the service valve.
2. If the ball is full of water you can unscrew it and replace just the ball.
3. If the valve is faulty remove the pipe via the compression fitting and remove the valve from the tank.
4. Install the new valve in the tank. When fitting the feed pipe it is advisable to check if the seal is a fibre washer seal or an olive compression fitting. It is an olive fitting, wrap a small amount of PTFE round the olive to ensure a water tight seal.
5.    Turn the water on and adjust the volume and height by adjusting either a screw on the end of the ball valve or bend the ball valve arm up or down (it is brass and should bend ok but can snap)

How to add two water tanks together

When joining tanks together, use 4 tank connectors. Two at low level and two at high level. This should help them balance out. After you have connected the tanks together it is imperative to prevent one tank from becoming stagnant. To do this, link the outlets to the system together. This is so the tanks are used equally. If one tank has the outlet then water in the other tank will generally not be used. Also make sure both tanks have seperate ball valve feeds.