Limescale inhibitor for combination (combi) boilers

Stops limescale dead in the water


The CombiBuddy stops limescale in combination (combi) boilers...




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In many areas of the UK, such as the Thames Valley, Kent and East Anglia in particular, rain water will pass through rocks that contain calcium and magnesium. The water that filters through these rocks will partially dissolve these minerals. Your water supplier will remove this underground water, clean it, and send it to homes across your region. But the dissolved minerals remain. When the water is heated (especially over 63 degrees C) the calcium deposits will fall out of the water and adhere to surfaces. This is what's commonly called 'limescale'. It’s highly damaging to water heating equipment and costs consumers millions of pounds per year.


However, you don’t have to resort to fancy ideas of protecting water systems from the damaging effects of limescale. Water softeners are all well and good. But they are expensive, and require constant salt replenishment and maintenance. The problem with non-physical water conditioners, such as those that use electronic signals, is that they seem largely unproven, and manufacturers of these units are conspicuously reluctant to offer a money-back guarantee if they don’t work. Polyphosphate inhibitors almost exclusively use a ‘dosing’ unit which has tiny holes for the water to flow in and out. However, the holes block up with the powdery polyphosphate!


We have carried out research for many years on what works and what doesn’t. Over thirty years of attending to hot water appliances that are encrusted with limescale has revealed that there really is only one choice - Siliphos, silicate-polyphosphate. A Siliphos dispenser doses the water with silicate-polyphosphate. So in 2003 we set out to find the perfect Siliphos dispenser for combi boilers - and, after constant improvement, the CombiBuddy (and LimeStop) is the result. It’s stainless steel rather than plastic, and there’s no need to replace the Siliphos!


Siliphos is a widely-trusted food-grade material proven time and again to inhibit limescale formation. Its ability to combat limescale deposits is really quite remarkable as it both lays down a protective layer on the walls of the supply piping and inhibits calcium deposits. The CombiBuddy is a stainless steel cylinder packed with Siliphos, which can be fitted prior to ANY combination boiler. It's even suitable for drinking water! Replacement of the unit (every 2 years - at a discounted rate) can quite literally be a 5-minute job! We’ll even remind you when replacement is due. If you want to protect a whole-house installation, then opt for the LimeStop instead (see HERE). The LimeStop is a larger version of the CombiBuddy for whole-house water treatment.


The CombiBuddy is guaranteed to work...or your money back!*


CombiBuddy FAQs


What is the cost of the CombiBuddy?

£99.00 includes free delivery (free to UK mainland only).

What will be the annual cost of the CombiBuddy?

In two years, your CombiBuddy will need to be replaced, so the cost works out to just 13p a day...to stop limescale from ever forming in your combi boiler. Exchanging the unit can be just a 5-minute job for a plumber, and you may even be confident enough to do it yourself.

How much does it cost to install?

It should cost anything from £25 to £60 plus any fittings that your installer may need - although it is usually a straight fit, without much need for fittings. We charge £60 to fit a CombiBuddy - in the RG postcode area.

Can I install it myself?

Yes, if you feel confident with water fittings. All you’ll need is tube cutters and probably a couple of 15mm elbow fittings. We recommend that you fit an isolating valve, too.

What's the length of the CombiBuddy?

It's just 175mm (6½”).

What's the width?


What does it weigh?

1.5 kg

What's it made of?

Stainless steel, with brass fittings.

What's inside that inhibits limescale?

Siliphos, a food grade material called silicate-polyphosphate.

How does it inhibit limescale?

As water flows through the CombiBuddy it flows over the spheres of Siliphos - and they give up a slight amount of their coating. Siliphos inhibits limescale in two ways. First of all it makes the calcium molecules stay in suspension, rather than stick. Secondly it lays down a layer of silicate on the walls of pipes etc. This too helps to inhibit limescale sticking.

How much Siliphos is in there?

Approximately 400 grams

Why that particular amount?

Because it's the optimum amount to ensure limescale inhibition in combi boilers.

Do you offer a discount for a ‘multiple’ order?

Yes, we do. Please email us.

Should it be fitted horizontal or vertical?

Either, though vertical is ideal. If fitting horizontally, then it should be installed ‘tails up’.

Does the Siliphos 'run out' of its effectiveness?

Yes. We recommend replacing the CombiBuddy after two years. We will send you a reminder when that time is up.

Can I replace it easily?

Yes. We suggest that you fit isolation valves when installing the CombiBuddy so that you can do this as easily as possible. It’s then just a five minute job to do. Some of our customers ask their boiler-service engineer to do it while he is there. Make him a nice cup of tea, if you like, but the job will be done before the kettle has boiled.

Can't I just replace the Siliphos?

Replacing the Siliphos in any Siliphos-dispenser for an appliance isn't usually a straightforward job. There's also the likelihood of leaks afterwards. So we opted for a replaceable unit, rather than one which can be refilled. We trialled different options but found that this was ideal. It means you don't have to try and buy Siliphos, and there's no messy, soggy used Siliphos to bother with. We've made the CombiBuddy for an excellent price, so that it's actually economic to discard it and replace it with another unit. We currently charge £30 to replace it for you (RG area only), and your engineer may charge you about the same.

Is the water drinkable?

Yes, Siliphos is a non-hazardous food-grade material. It conforms to EN1208:2005 (Treatment of water intended for human consumption) and WHO standards for drinking water supplies. Unlike artificially-softened water, it's safe for babies too. The CombiBuddy unit itself is just stainless steel. The fittings used are brass (standard pipe fittings). There’s no requirement for the CombiBuddy to be WRAS approved for use with mains water drinking supplies as it is made of stainless steel and brass with an approved food-grade material. WRAS is the Water Regulations Advisory Scheme

Do you supply a ‘check valve’ anyway?

Yes, we do. It’s in the box.

Is the CombiBuddy classed as a water softener?

No, the hardness is still there, it's just suspended. This is true of all limescale inhibitors; if it doesn't actually remove the 'hard' salts then it's not a water softener. We actually prefer to call it a water conditioner, but ‘limescale inhibitor’ is the often-used term.

If the treated water is then stored, will it still be effective?

The effect diminishes with time. All such limescale inhibitors only ever affect moving water. The sooner the stored water is used, the better.

Your instructions say not to fit the CombiBuddy too close to the boiler, why?

Warm water backfeeding down the supply will degrade the Siliphos. Its period of effectiveness would be less.

Can I fit it in a warm cupboard?

Yes, but not if the ambient temperature is above 30 degrees C for the same reasons as above. Also, fit it low down in the cupboard where the cold mains enters.

Will it protect mains thermal store appliances or my home?

For that we recommend a LimeStop TS. Most mains thermal stores use a coil of mains cold water that is heated by surrounding hot water. This is increasingly common. However, such units rapidly 'scale-up' in hard water areas. See www.limestop.co.uk

Will I still get limescale around my showerhead?

Most possibly, yes. This is because the Siliphos-effect will stop your shower scaling-up, but 'still' water will be left on the showerhead and around taps etc. The effect will be lost and deposits may well occur.

What will the CombiBuddy protect?

The CombiBuddy is ONLY made for fast-flowing mains water, and is thus ideally suited to combination boilers. It can also be used to protect electric showers, etc.

Can I fit it to a conventional hot water cylinder?

No, this would be a stored system.

Can I fit it on my central heating system?

No, it is made for mains cold water supplies, not central heating. You shouldn't get any limescale in your heating system providing it has been installed correctly. If you want to stop magnetite sludge (black, oily substance) then fit one of our BoilerGuard or MagnaMate units.

What size ports has the CombiBuddy got?

The CombiBuddy is supplied in 15mm compression fittings as standard.

What if I have ¾" or 22mm water supply?

This would be unusual, as combi boilers almost always have a 15mm water supply - so check and make sure before you order. Just measure the width of the supply pipe. If in doubt, email us.

Will my water pressure be reduced?

The CombiBuddy is a through-flow unit, and you would not see any noticeable drop in water pressure or flow after fitting.

Will the CombiBuddy withstand high water pressures?

Yes. Unlike some plastic units, which are tested to 10 bar, the CombiBuddy - being made of stainless steel - will withstand extraordinarily high pressures.

What is limescale?

It's dissolved rock. Rain water dissolves the calcium and magnesium out of the rock. This water is then treated and sent to your home. When the water is heated the dissolved particles re-solidify and stick to the walls of the heat exchanger. It will do this at low temperatures, but it really begins at anything above 63 degrees C.

Is limescale harmful?

To your heating appliances, yes, very! Even a slight coating of it will reduce the efficiency of your appliance, meaning your energy bills will be higher. It also causes premature failure of key components.

Do you guarantee that the CombiBuddy works?*

Yes. Our guarantee is that the secondary (hot water) heat exchanger of your combi boiler will not suffer from 'scaling-up'. If it did then we would refund the initial purchase cost. We believe all limescale inhibitors should carry a performance guarantee.  Don't buy one that hasn't got a money-back guarantee.

Any clauses to that?*

Yes, you must have had the unit at least two years, and obviously that you had replaced it at the recommended intervals. You would be required to provide proof of purchase.

Why is the CombiBuddy better than other limescale inhibitors?

The CombiBuddy requires no electricity or maintenance. It doesn't use magnets or questionable electromagnetic waves. It uses a time-proven material that we feel good enough to offer our performance guarantee of your money back. However, it also goes a few better than very similar units because it's metal, not plastic, and doesn't require that you fiddle with large 'O' rings and wet Siliphos! You may be aware of a very similar unit to ours, but it requires 6-monthly topping up, and annual cleaning, and Siliphos replacement. With ours you simply replace it every two years, having a nice clean one ready to go for minimum fuss. It’s recyclable, as it’s stainless steel.

Have you ever had to give anyone their money back due to an appliance re-scaling?

No, never.

How much is it?

£99.00 including postage.

And when it’s ready to be replaced?...

We contact you.

Do you give a discount if I buy more than one?

Yes, please email us.

Is the CombiBuddy a British product?

Yes, we're proud to say it is. It is a quality product hand-made in England, not China - like so many similar units.

I have soft water, so surely I don’t need a CombiBuddy?

The CombiBuddy can even be used in soft water areas, as the Siliphos lays down a protective coating on the walls of the supply piping - thus preventing acidic-water attack and so-called ‘Blue Water’.

Why don’t you sell the CombiBuddy in plumbing merchants?

Because by the time they have added their mark-up charge, it would make it too expensive. You get it the cheapest possible by buying direct from us.

I want one.

Then just click on the BUY button at the top of this page.

Still unsure?

Read this


Why we are not on Amazon.

We don’t support Amazon, and its woke politics of cancel culture. We will not buy any products from Amazon and will not have anything to do with the company.


Why we will NOT offer PayPal.

PayPal is a very ineffective and poor payment facilitator. It does NOT protect you in many circumstances, and its ‘Resolution Service’ even circumvents British consumer law! It isn’t good for us, because PayPal’s charges would make our products more expensive, and it isn’t good for you because it takes too long to settle any disputes. We advise that you are much safer using your credit card, as that protects you under Section 75 of the Consumer Credit Act. What is actually needed is a government-controlled escrow scheme. Don’t hold your breath waiting for that!



Made in Berkshire, England


Prices correct as of July 2, 2020




The guarantee against ‘scaling-up’ is dependent on the LimeStop being installed for 30 months and at least one replacement. If the protected appliance/s* should ‘scale-up’ to the detriment of water flow (we would require proof to satisfy such an occurrence), then we would return the original purchase price to the original purchaser minus the delivery charge. Your statutory rights are not affected.

*Protected appliance/s: The unit purchased must be stated as suitable for its application.











Truly remarkable limescale inhibitors

Stop limescale...or your money back...GUARANTEED

...from 1/6th the price of a water softener!