An inhibitor does not remove hardness. It alters how the minerals crystallise so that scale does not adhere to heat exchange surfaces. That protects the boiler and cylinder effectively and cheaply, but you still have hard water at every tap, and the effect diminishes with distance.
The honest distinction
A water softener removes calcium and magnesium from the water by ion exchange. After a softener, the water genuinely is soft: it will not form scale anywhere, it changes how soap behaves, and it affects the whole house.
A scale inhibitor does not remove anything. The minerals are still there. What an inhibitor does is interfere with the crystal formation so that, instead of growing as hard adherent deposits bonded to hot metal surfaces, the calcium forms tiny non-adherent particles that pass through and out with the water.
Both protect a boiler. Only one changes your water. Anyone selling an inhibitor as ‘a softener without the salt’ is describing something that does not exist, and it is worth being alert to that phrase.
| Softener | Inhibitor | |
|---|---|---|
| Removes hardness | Yes | No |
| Protects boiler and cylinder | Yes | Yes, effectively |
| Soap lathers better, no scum | Yes | No |
| Stops scale in kettles, taps, showers | Yes | Only partially, and less with distance |
| Needs salt | Yes | No |
| Needs a drain and power | Yes | No |
| Space required | A cabinet | A small in-line unit |
| Ongoing cost | Salt | Little or none, depending on type |
The types, and how much to believe about each
Polyphosphate dosing
A cartridge slowly releases food-grade polyphosphate into the water, which sequesters the calcium and prevents it depositing. This is well-established, genuinely effective for protecting appliances downstream, and used widely in commercial catering. The cartridge is consumable and must be changed on schedule – an exhausted cartridge provides nothing, and this is the most common reason an inhibitor ‘stops working’.
Electrolytic and sacrificial zinc
An in-line device with a zinc or similar element that alters crystal nucleation. Modest, real effect on the run immediately downstream. Effect reduces with distance and time, and it is a protection device rather than a treatment.
Magnetic and electromagnetic conditioners
A magnet or coil clamped to the pipe. The evidence for these is genuinely mixed – there is laboratory work suggesting an effect on crystal morphology, and there is a great deal of unsupported marketing. Our position is that we will fit one if a customer wants one, but we will not tell you it is equivalent to a softener or claim a performance figure we cannot support.
Ask whether the manufacturer is claiming scale *prevention on heat exchange surfaces*, which is a defensible claim, or *water softening*, which for a device that removes nothing is not. The first is a real product category. The second is marketing.
When an inhibitor is the right choice
Genuinely often, and we would rather fit the proportionate thing than the expensive thing.
- A flat or small house where there is no room, no drain and no appetite for handling salt.
- A rental property, where a softener needs a tenant to maintain it and an inhibitor does not.
- Protecting a specific appliance, such as a combi boiler’s plate heat exchanger, where the concern is the boiler rather than the whole house.
- As a stopgap where a softener is planned but not yet practical.
- Where the budget does not stretch, and the alternative is doing nothing at all. Some protection is substantially better than none.
And when it is not the right choice: where the real complaint is scale on taps, shower screens, kettles and glassware; where there is a large hot water cylinder you want properly protected; or where soap, detergent and skin comfort matter to the household. Those are softener problems.
Fitting and maintaining one
An inhibitor goes on the cold feed, before the appliance or appliances it is protecting. For whole-house protection that means on the rising main after the stopcock; for boiler-only protection it can go on the cold feed to the boiler alone, which is cheaper and entirely legitimate.
Isolation valves either side are worth fitting, because a cartridge type needs changing and nobody wants to drain the house down to do it. Cartridge replacement intervals are specified by the manufacturer and depend on hardness and throughput – and the single most common failure mode is simply not replacing it. If you have an inhibitor and cannot remember when the cartridge was last changed, it is probably doing nothing.
Not sure which you need? It mostly comes down to whether you have a cylinder and how much hot water the house uses.
Questions we get asked about this
Does a scale inhibitor soften water?
No. It does not remove calcium or magnesium, so soap still will not lather properly and you will still get scale on taps and in kettles. It prevents scale adhering on heat exchange surfaces, which protects the boiler – a different and narrower job.
Do magnetic conditioners actually work?
The evidence is mixed. There is credible research showing an effect on crystal formation, and there is also a lot of marketing that goes well beyond it. We will fit one if you want one and we will not claim it is equivalent to a softener.
How often does the cartridge need changing?
Whatever the manufacturer specifies for your hardness and water usage – typically measured in months rather than years. An exhausted cartridge provides no protection at all, and a forgotten one is the usual reason an inhibitor appears to have failed.
Can I have both an inhibitor and a softener?
There is no point. A softener has already removed the hardness, so there is nothing left for the inhibitor to act on.
Will it protect my existing scaled-up boiler?
It will slow further deposition, but it will not remove what is already there. If the heat exchanger is already scaled, that needs addressing directly before the inhibitor has anything useful to do.
Does my boiler manufacturer require one?
Several specify water treatment in hard water areas, and some make it a warranty condition. Check the installation manual for your specific appliance – and in this county it is worth doing whether they insist or not.
What happens when you call
Call and describe it
You speak to an engineer, not a call centre. Most jobs can be narrowed down on the phone.
We look at it properly
A real diagnosis before a price, and a straight answer if it is not worth doing.
A written quote
Itemised, so you can see what you are paying for.
The job, and the paperwork
Certificates where the work needs them, and what will need attention next.
Where we do this work
Across Norwich and the whole of Norfolk. If you are on the edge of the county, call and ask — we will tell you honestly whether we are the right people.
- Norwich
- Wymondham
- Dereham
- Attleborough
- Aylsham
- North Walsham
- Cromer
- Diss
- Loddon
- Long Stratton
- Watton
- King's Lynn
Need this doing?
Call and describe the problem — you will speak to an engineer, not a call centre. Written quotes, no estimates over the phone.