Review
Doulton HIP DUO review: choosing an extra pre-filter
The HIP DUO pairs a Biotect Ultra cartridge with one pre-filter you choose from five, in a different housing from the Kingfisher. At £304.95 for the system, or £349.90 with a pillar tap, it makes sense only if you have a specific concern one of those pre-filters is sold for and you are content to rely on Doulton’s own description of it.[1]
Research-based review. Manufacturer documents and published evidence where available. Tap Sorted has not tested this product. We may earn a commission through links marked Affiliate link, at no extra cost to you.
Photo: Doulton
- Price
- £349.90 with the pillar tap (£304.95 system + £44.95 tap)
- Replacement
- Biotect Ultra 2501 £29.45, about every 6 months; 9A04 limescale pre-filter £36.45, about every 3 months
- Five-year cost
- £1,307.50, hardware and cartridges, before fitting
- Evidence
- Manufacturer claims; no independent listing confirmed
See the HIP DUO at Doulton Affiliate link 9A04 limescale pre-filter Affiliate link
Read the running cost first. With the 9A04 limescale pre-filter on Doulton’s recommended three-month cycle, five years comes to £1,307.50, against £564.95 for the Kingfisher: £742.55 more, for a stage that has no independent listing that we found.
Who it suits
- have a particular concern that one of the five pre-filters is sold for, and have read Doulton’s page for it
- want hot, cold and filtered water from the three-way mixer tap
- accept the maker’s claims for the pre-filter without a registry entry
Who should look elsewhere
- want the NSF listing the Kingfisher has, because it does not carry over
- want a predictable running cost: only the 9A04’s interval is known
- want one price that includes the tap
What the second stage adds
One pre-filter is included, chosen from limescale (9A04), PFAS and chlorine (9H04), nitrate (9F04), sediment (9E04) and fluoride (9B04), The 9A04 replacement is £36.45; check the individual product pages for the other pre-filters’ prices.[1][2] They fit only the DUO and TRIO. What each does is Doulton’s description, with no independent validation that we found, so we quote no removal figure and would not buy on the name alone.
Why the Kingfisher’s listing does not apply
Doulton’s own FAQ says the Biotect Ultra was NSF-tested in the EcoFast housing, not in the DUO or with its pre-filters.[1] The Kingfisher’s listing therefore says nothing about this system, and we count the HIP DUO as maker’s claims only.
The price once the tap is counted
The system is sold without a tap. Fitting is extra either way.
| Configuration | Parts | Total |
|---|---|---|
| System only, no tap | HIP DUO system with Biotect Ultra, installation kit and one pre-filter £304.95[1] | £304.95 |
| With pillar tap | HIP DUO system with Biotect Ultra, installation kit and one pre-filter £304.95[1] Pillar tap £44.95[3] | £349.90 |
| With three-way mixer tap | HIP DUO system with Biotect Ultra, installation kit and one pre-filter £304.95[1] Three-way mixer tap £199.95[4] | £504.90 |
Running costs over one, three and five years
The Biotect is £29.45 every six months. The 9A04 is £36.45 and Doulton recommends about every three months, depending on your water.[2] It is the only pre-filter whose interval we have, so the table assumes it. Over five years the 9A04 alone is £692.55 of the total. A different pre-filter could cost more or less, and we cannot price it.
| Case | 1 year | 3 years | 5 years |
|---|---|---|---|
| With tap, with the 9A04 pre-filter | £488.70 | £898.10 | £1,307.50 |
Same sums and assumptions as the comparison: 8 litres a day, the cartridge fitted at purchase included, no fitting, adaptors or water.
Fitting and cartridges
The housing takes the Biotect Ultra 2501 and 2505 SI and the DUO and TRIO pre-filters, and not the Ultracarb 9501, 9505 or 5594 or the gravity 8674 and 8B76.[1] Doulton’s page labels the dimensions inconsistently with its photograph, so we quote none: check the installation drawing and the clearance for changing cartridges before you measure the cupboard. The cartridge matrix and the taps page cover compatibility. Read the installation guide before arranging fitting.
Alternatives
- Doulton Kingfisher with Biotect Ultra review (in the comparison): One cartridge, a registry listing for this exact system, and less than half the five-year cost.
- Aquaphor Crystal three-stage review (in the comparison): Three stages and a tap in the box for £129.99, with maker’s claims only.
- UK Water Filters Anti-Scale kit review (in the comparison): If limescale is the reason, this is sold for it at £97, with no independent confirmation either.
For all six side by side, with matched totals, see the under-sink comparison, or all the reviews.
Common questions
Which pre-filter should I choose?
That depends on your concern and your water. Doulton describes each on its page; we do not recommend one, and quote no removal figures for any of them.
Does the HIP DUO work with the three-way tap?
Yes: Doulton lists the three-way mixer tap as compatible, which takes the hardware total to £504.90 before fitting.
Is it NSF certified?
We found no registry entry for the HIP DUO. The Kingfisher’s listing names a different housing.
Sources
- Doulton: HIP DUO under-sink system with Biotect Ultra read 16 October 2026
- Doulton: 9A04 limescale pre-filter for DUO systems read 16 October 2026
- Doulton: pillar tap read 16 October 2026
- Doulton: three-way mixer tap read 16 October 2026
How we check · Prices checked 16 October 2026 and subject to change.