Fitting a Cold Water Storage Tank

cold water storage tank

Checking the condition of the cold-water storage tank in your loft is important. Not only does this tank supply a lot of your water, it also has the potential to cause a lot of damage should it spring a leak. In a worst case scenario, should a leak occur when you are away (on holiday for example) you could come back to hundreds of litres of water ruining your carpets and furniture. If you have an old galvanised steel tank, it is probably time you thought about fitting a new one.

Fitting a new cold water storage tank is not the easiest of DIY jobs, so make sure you are familiar with the skills involved. You will need to know how to Bend and Join Copper Pipes, as well as having an idea of how the gravity-fed cold water system works.

Tools and Materials

Make sure you have everything you need before you start this job. The rest of your family will not be amused if they have to go without water for a few days while you put the job on hold to find fittings and tools you didn’t realise you needed. As a bare minimum, you will need:

cold water storage tankStorage Tank
Have a look at the size of the existing tank and buy one which is equal to or slightly larger in size. Be wary of increasing the size of the tank too much unless you are sure the joists can take the added weight. You can buy tank kits which come complete with a float valve, insulation jacket, some fittings and a tank plate for around £100 (depending on the size of the tank you need).

Plastic Pipe
Check what size pipe you need to link up to the existing outflow pipe. Buy enough lengths of matching pipe to be able to connect to this pipe easily. Also get tank connectors (if not supplied with the tank kit) and compression joints to fit the pipe.

Copper Pipe
Buy a few lengths of copper pipe along with connectors and compression joints. You will need this to connect the tank to the rising main pipe and to link up the various distribution pipes. The connectors you need will vary, depending what comes with the tank kit. If unsure, ask at your local builders or plumbers merchants.

You will need a hacksaw, PTFE tape, adjustable spanner and a rubber mallet can be useful. If you can borrow a pipe cutter and a pipe bender, do so, it will make the job a lot easier. You can buy both of these tools fairly cheaply. Make sure you have enough light (if the loft is not fitted with a mains light) to work by. A head torch is also handy.


The first thing you need to do is prepare the system to be worked on by draining it of water. Turn off the boiler to stop it drawing water and then turn on the cold taps in the bathroom. Turn off the water at the stopcock on the rising main and wait until the cold taps stop flowing. Now get up into the loft with a bucket and scoop out the remaining water from the drained tank.

Locating the Stopcock – The location of the stopcock varies from house to house, so you may need to search around a bit to find it. The most likely places are under the kitchen sink, under the stairs or possibly in the basement if you have one. It is important that you know where the stopcock is in case of a plumbing emergency.

Removing the Old Storage Tank

Loosen and remove all of the pipes connected to the old tank and get ready to move it. If the tank is an old galvanised type, you will need to have a sheet of hardboard or something similar for it to sit on while you work on the new tank. Once this is in place, drag the old tank over to it and ensure the weight is evenly distributed. With a plastic tank, you can probably just lower it out of the loft straight away.

Make a note of which of the existing pipes are which. It should be fairly obvious which pipes are distribution pipes and which is the supply pipe (distribution pipes will connect at the bottom of the tank and supply pipes at the top) but it is always best to be sure.

Fitting the New Storage Tank

Check that the platform that held the old tank is sound. If it is not, replace it with a sheet of hardboard at least 25mm thick. Position the tank on the hardboard so that the existing connection pipes match as closely as possible to where yo want the tanks’ inlet and outlet holes.

It is unlikely that the existing pipes will align perfectly with the new tank, so you will need to extend or shorten them accordingly. Start with the distribution pipes, altering them until they touch the outside of the tank. Drill holes of the correct size (depending on the size of the tank connectors and pipes involved) in the side of the tank to fit the tank connectors. These should be around 60mm from the bottom of the tank, but be guided by the height of the existing distribution pipes. If the existing pipes do not have gate valves already fitted (most should), you will need to add some.

tank connectorFit the tank connectors to the new tank, remembering to include the rubber washers on either side of the tank wall. Also make sure you wrap PTFE tape around the threaded tail before screwing on the nut and tightening it. Match up the pipes with the newly fitted tank connectors and tighten the compression joints fully.

You can now alter the existing overflow pipe so that it lines up to the tank. The overflow pipe should be positioned about 100mm down from the top of the tank. Fit the plastic tank connector for the overflow pipe in the same way as the connectors for the copper pipes. Connect up the existing pipe to the tank connector and tighten up all the fittings.

Fitting the Float Valve

Alter the copper supply pipe, if needed, so that it reaches the side of the new tank. The new hole for the supply pipe should be drilled slightly higher than the hole for the overflow pipe (about 25mm higher should be fine). Fit the float valve into the hole, again remembering to use the rubber washers and PTFE tape, and attach the tank support plate. Connect the existing supply pipe to the compression fitting on the float valve and tighten it.

Filling the Storage Tank

Open up the stopcock and wait until water begins to flow through the open bathroom cold taps. Turn the taps off and go back up into the loft to watch the storage tank fill up. Check carefully as each new tank connector is submerged to ensure that nothing is leaking. If you do notice leaks, you will need to drain the tank as before and double check the connectors. Assuming all is fine, wait until the water reaches the overflow pipe and adjust the float valve arm so that the water level is held just below it. Finally, fit the insulation jacket and the lid of the tank to finish off.

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