Your cold water storage tank is usually found in the loft, near a smaller expansion tank. It’s a crucial component of a gravity-fed plumbing system, supplying cold water to taps, showers, and indirectly to your hot water system via the hot water cylinder. As water is drawn from your hot taps, the cold water storage tank refills the cylinder by gravity, usually positioned 3 to 4 metres above it.

Your cold water tank can degrade over time and spring leaks, to the point where you may need to replace it. We’ll go through all the costs of replacing your cold water storage tank in this guide.

How much does it cost to replace a cold water tank?

Cold water tank replacement typically costs from £200 to £500, depending on access, tank size, and the complexity of the job:

At HaMuch, we use our database of hourly and daily rates of plumbers across the country to estimate how much cold water tank replacement will cost in your local area. Take a look at our cold water tank replacement cost table and find your nearest town or city to get a more accurate idea of price for your location.

Cold water tank brands and types

To help you get an idea of how much a new water tank will cost, here are some of the most popular brands and types available:

Image	Name	Cost
	Polytank 25 Gallon/114 Litre Cold Water Loft Tank	£115.20
	Kingspan 227 Litres Cold Water Circular Loft Tank	£267.59
	Polytank 40 Gallon/182 Litre Framed Cold Water Loft Tank	£330.00
	Polytank 100 Gallon/454 Litres Cold Water Tank	£356.40

Common issues with cold water storage tanks

One of the main challenges when you replace your cold water tank is getting the new tank through the loft hatch and removing the old one. If access is simple, the cost may be limited to just a few hours of labour and materials. ‘Coffin tanks’ are often used in lofts, as their slimline shape makes them easier to fit through standard hatches.

If a plumber diagnoses a small leak or damage during inspection, it might be possible to patch the tank or make a quick repair, reducing the cost to under £100. However, if you’re moving the tank as part of a loft conversion, and your existing unit is several years old, it may be more cost-effective to install a new one. Relocating an older plastic tank can risk cracking, and a new tank can offer peace of mind and longevity.

How do I know when my cold water storage tank needs replacing?

Cold water tanks are generally made of polyethylene plastic and should last around 10 years. Signs your tank may need replacing include:

• Visible cracks or splits
• Signs of leaking
• Brittle, aged plastic that risks further damage
• Contaminated water from a missing or damaged lid

When your plumber visits your property to quote, they should be able to tell you whether they can repair your tank or whether it’s more cost-effective to replace it.

Can my cold water storage tank be moved to a new location?

Yes, you can move your cold water storage tank to a new location if you are planning a loft conversion or need it moved for better access to your loft. However, there are a few things to consider. 

If you live in a maisonette or older property, your cold water supply might be shared with neighbours. In that case, moving the tank may disrupt the water supply for both households.

Since these systems rely on gravity, the tank must be installed at least 2 metres above showers and hot water cylinders. During a move, many plumbers prefer to replace older steel or copper tanks with modern plastic versions. The old tank often needs to be cut apart for removal.

Ensure the new location allows access for future maintenance and that the tank is properly lidded and insulated.

Can a cold water storage tank be repaired?

In some cases, a cold water storage tank can be repaired. Minor cracks or holes above the water line can often be sealed with a waterproof sealant. If the damage is below the waterline, the tank may need draining, followed by plastic welding or sealant work. There is always a risk that attempting a repair could worsen the damage, making replacement inevitable.

Another option is relining the tank using WRAS-approved polyurethane coatings, suitable for potable water. Other small fixes might include replacing a warped lid or refreshing insulation. If there are signs of bacterial contamination, for example if the lid has been missing, a professional hygiene clean may be needed to prevent Legionnaires' disease from Legionella bacteria.

Do I need a cold water tank if I have a combi boiler?

No, you don’t need a cold water tank if you have a combi boiler. Combi boilers are mains-fed systems, which heat water on demand without storing it. If you have a combi boiler, you won’t need a cold water storage tank.

If you recently replaced your old gravity-fed system with a combi boiler, you may still have your cold water tank in the loft, as your heating engineer can just drain it and cut off the supply. There’s no reason why you need to have it removed, but if you’d like more space in your loft, many tradespeople will remove it for you.

Ready to replace your cold water storage tank? Post your job on HaMuch now and we’ll put you in touch with local plumbers who are ready to help.

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