Overview | Is this right for me? | What it reduces | How it works | Specs | What's included | Installation | Maintenance & costs | FAQs | Reviews

• How Hard is My Water? - find out how hard your water is and what it means for your home.
• OneFlow Anti-Scale System FAQ - the questions we get asked most about OneFlow, answered.

Overview

The Boiler Descaler is a salt-free scale prevention system that uses template-assisted crystallisation (TAC) to protect your pipes, plumbing and appliances from the effects of hard water. Rather than dosing your heating system with chemicals, it treats the water on the way in - so scale never gets the chance to form on your boiler or heater in the first place.

• Protects your boiler, water heater and immersion element from scale, and the loss of efficiency that comes with it.
• Salt-free and chemical-free - no control valve, no electricity, and no waste water.
• Treats all the water, including your radiators, from a simple "water in / water out" installation.
• Suitable for properties up to 3 bedrooms with 1 or 2 bathrooms, at flow rates up to 18 litres per minute.
• Virtually maintenance free - just replace the OneFlow cartridge every 1-2 years, and you can do it yourself.
• Also suitable as an undersink mains water filter.

Live in a hard water area? - If you've had to buy a new kettle every year or two, your boiler is quietly suffering the same fate.

Is this right for me?

Choose this if

You live in a hard water area and you want to protect your boiler, water heater and plumbing from limescale - without the salt, electricity, waste water and floor space that a conventional water softener demands. It's an ideal fit for a property of up to 3 bedrooms with 1 or 2 bathrooms.

Not ideal if

You need a higher flow rate for a larger property (take a look at our OneFlow 30 LPM or OneFlow+), or you also want to remove chlorine and improve taste and odour - in which case the Moby Taste and OneFlow pairs a carbon block with the OneFlow cartridge. It's also not a water softener, so if you specifically want soft water rather than scale protection, see our water softeners.

What to check before buying

• Available space: allow a total height of 47cm (the housing is 40cm, plus 2cm above and 5cm below for cartridge changes), a width of 20cm plus room for your port connections, and a depth of 22cm when mounted.
• Ports kit: the housing has standard 1" BSP female ports. Choose a 15mm or 22mm connections kit (with or without isolating flexis), or select 'no port connections' if you're supplying your own.
• Flow rate: this system is rated up to 18 litres per minute, which suits properties up to 3 bedrooms with 1 or 2 bathrooms. Larger homes need a higher flow rate system.
• Your water hardness: OneFlow is designed for hard water, but if your water is harder than 25 grains (427 ppm CaCO3) it may not be suitable. Check with your local water supplier, who can tell you your hardness measurement. A TDS meter may read higher because it measures all total dissolved solids, not just CaCO3.

What it reduces and what it doesn't 

The Boiler Descaler reduces:

• Limescale formation - on pipes, fittings, valves, hot tanks, heating elements and appliances
• Existing scale - the treated water gradually clears residual scale already sitting in your pipework
• Energy waste - by keeping heat transfer surfaces free of scale

The Boiler Descaler doesn't reduce:

• Water hardness - it prevents scale forming, but it doesn't soften your water or remove the dissolved minerals
• Beneficial minerals - calcium and magnesium are deliberately retained
• Chlorine, taste and odour - there's no carbon stage in this system
• Fluoride
• Bacteria and micro-organisms
• Sediment, heavy metals and other contaminants

OneFlow is not a water softener. It doesn't add chemicals into your water or remove the beneficial minerals - which is exactly why the water stays drinkable.

How it works

The problem: scale is costing you money

Scale built up in your water heater or boiler can seriously harm its efficiency, and the damage limescale does means the elements or the entire unit will need replacing. The working life of anything that heats hard water is much shorter than it should be - in fact, you may only get half the expected time before you have to replace it.

If you live in a hard water area you've probably already had to buy a new kettle every year or two. It's the same with gas boilers and electric water heaters, and even if you don't have a multipoint boiler, the element in your immersion heater will also get fouled with limescale. With boilers costing thousands and only lasting a few years instead of the 10 years you were promised, it's not a great situation to be in. Immersion heater elements aren't so expensive, but it's a real hassle getting them replaced.

Then there's the loss of efficiency. A scale-fouled boiler or heater could be operating at only 50% efficiency - meaning it takes twice as much energy to heat the water to the temperature you want. Your energy bills could be almost double what they should be, just because you live in a hard water area and don't control the scale build up.

The solution: template-assisted crystallisation

OneFlow uses a process called template-assisted crystallisation, or TAC. The dissolved minerals calcium carbonate (CaCO3), magnesium carbonate (MgCO3) and bicarbonate (HCO3) combine into microscopic crystals on the TAC media's nucleation sites. These microscopic crystals then detach from the media and flow freely through the plumbing system instead of creating hard scale.

The result is scale protection that treats all the water, including your radiators, from a simple "water in / water out" arrangement - with no chemicals added, so the water is drinkable too.

Specifications

Technology	Template-assisted crystallisation (TAC) - salt-free scale prevention
Cartridge	Watts canister containing 750ml of A8210 OneFlow anti-scale media
Cartridge size	4.5" x 10"
Recommended flow rate	Up to 18 litres per minute
Suitable for	Properties up to 3 bedrooms with 1 or 2 bathrooms
Maximum operating pressure	125 PSIG (approx 8.6 bar)
Operating temperature	10ºC - 52ºC (50ºF - 125ºF)
Connection size	Standard 1" BSP female ports; 15mm and 22mm connections kits available
Dimensions	Height 40cm (total height required 47cm) x width 20cm (plus port connections) x depth 20cm (22cm when mounted)
Requirements	No control valve, no electricity, no waste water
Certification	Tested and certified under NSF/ANSI Standard 42 (materials only); FDA grade components and materials
Maintenance	Replace the OneFlow cartridge every 1-2 years

*Dependent on local water chemistry, flow rates, system design and application. Performance claims apply to a fully installed system with filter, housing, and connection to pressurised water.

What's included

• 1 x big blue filter housing (standard 1" BSP female ports)
• 1 x white housing bracket
• 1 x Watts OneFlow cartridge
• 1 x housing spanner
• Fitting instructions for your plumber

Choose your ports kit at checkout: 15mm or 22mm connections (with or without isolating flexis), or no port connections if you're supplying your own.

Installation & placement

Installation is a simple "water in / water out" arrangement on your cold water supply - you'll only need to call the plumber in once. Allow a total height of 47cm, a width of 20cm plus your port connections, and a depth of 22cm when mounted. It's also suitable as an undersink mains water filter.

Fitting instructions for your plumber are supplied, and can also be downloaded here.

Important information about TAC media: add water to the canister containing the TAC media and leave it to stand for two hours before dropping it into the housing. If you don't do this, some of the smaller particles can escape into the pipework and be lost.

Maintenance & running costs

OneFlow is virtually maintenance free. Just replace the OneFlow cartridge every 1-2 years - and changing the cartridge or media is a simple job you can do yourself, with no need to call the plumber back. There's no electricity supply, no brine tank, no salt pellets to feed it every week, and no backwashing requiring a two hour shutdown.

Replacement OneFlow cartridges are available here, and you can also buy replacement TAC media on its own - choose the 750ml refill volume for the boiler descaler. We'll email you every 6 months to remind you to check your filter performance, and we recommend changing your housing O-ring every 2 years.

FAQs

How does limescale affect my energy bills?

A scale-fouled boiler or heater could be operating at only 50% efficiency, which means it takes twice as much energy to heat your water to the temperature you want. Your energy bills could be almost double what they should be, purely because you live in a hard water area and aren't controlling scale build up. Scale also shortens the working life of anything that heats hard water - you may only get half the expected time before it needs replacing.

Why not just use a chemical boiler descaler?

Chemical descalers have to be introduced into the heating system, and usually require you to drain down the plumbing and then fully flush it afterwards. It's all a bit of a faff, and quite daunting for most people to do themselves. A scale conditioning filter is a much smarter method: it strips out existing scale and then prevents more scale forming in the future, and you'll only need the plumber in once to install it.

Is this a water softener?

No. OneFlow is not a water softener. It prevents scale by converting the hardness minerals into harmless, inactive microscopic crystals, rather than removing them by ion exchange. It doesn't add chemicals to your water or strip out the beneficial minerals like calcium and magnesium - and it needs no salt, no electricity, no brine tank and no waste water discharge.

How long before I notice a difference?

OneFlow starts working right away, but there will be residual limescale in your water pipes that can take up to three months to clear before you start noticing the difference. Perseverance is worth it.

Does it remove chlorine?

No - there's no carbon stage in this system, so it won't reduce chlorine or improve taste and odour. It's worth knowing that the efficiency of OneFlow is greater if the water is filtered for chlorine first, so if you want both, take a look at the Moby Taste and OneFlow, which pairs a carbon block cartridge with the OneFlow cartridge.

What size property is it suitable for?

It's rated up to 18 litres per minute, which suits properties of up to 3 bedrooms with 1 or 2 bathrooms. For larger homes or higher flow rates, take a look at our OneFlow 30 LPM or OneFlow+ systems.

How often does the cartridge need changing?

Every 1-2 years, and it's a simple job you can do yourself. We'll email you every 6 months to remind you to check your filter performance, and we recommend changing the housing O-ring every 2 years.

* Watts components are sometimes replaced with other similar quality items due to supply chain issues. Brassware and other plumbing accessories are sourced from UK suppliers.

Reviews

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