Kohler Mira Limited v Norcros Group (Holdings) Limited

A patent claim to an instantaneous water heater must be construed by reference to the heater itself, rather than to the use or larger apparatus in which it may later be installed. Where the claim says that a diverter valve is “configured so that” a result is achieved, the valve must achieve that result, although other components of the heater may contribute. General claim language should not be confined to a preferred embodiment. A term such as “substantially unchanged” is insufficiently certain where the specification supplies no criterion for deciding its boundaries. A fuzzy boundary may be permissible, but a boundary whose location cannot be ascertained is not. The patent was therefore revoked for insufficiency, and the products did not infringe even on the assumption that the patent was valid.

Kohler Mira Limited alleged that Norcros Group (Holdings) Limited’s DuElec electric showers infringed claims 1 and 4 of a patent for an instantaneous water heater with a downstream diverter valve. HHJ Melissa Clarke, sitting in the Intellectual Property Enterprise Court, granted infringement relief by an order dated 9 January 2025, for the reasons given in [2024] EWHC 3247 (IPEC). She rejected challenges based on uncertainty, excessive claim breadth, novelty and obviousness.

Norcros appealed on construction, infringement, uncertainty, excessive claim breadth and obviousness. Mira served a respondent’s notice alleging infringement by equivalents. The central issues were the meaning of “configured so that”, the meaning and certainty of “substantially unchanged”, and whether the products infringed on either the normal construction or by equivalents.

The appeal was allowed. Lord Justice Arnold gave the lead judgment. Lady Justice Falk and Lady Justice Asplin agreed. The Patent was revoked for insufficiency, and Norcros’s products did not infringe claims 1 and 4 even if the Patent were valid.

1. Patent claims are purposively construed by asking what the skilled person would understand the patentee to mean from the language of the claim read in the specification as a whole. Claim construction is a question of law. The approach stated by Lord Hoffmann in Kirin-Amgen Inc v Hoechst Marion Roussel Ltd [2004] UKHL 46; [2005] RPC 9 was applied.
2. Claim 1 was a claim to an instantaneous water heater, not to a shower or any larger apparatus in which the heater might be installed. The requirement that the diverter valve be “configured so that” the flow rate was substantially unchanged meant that the diverter valve had to achieve that result. Other components of the instantaneous water heater could contribute, but infringement could not depend on the heater’s use or intended use in a larger assembly.
3. “Substantially unchanged” could not be confined to Mira’s proposed risk-of-scalding criterion. General claim language should not ordinarily be restricted to a preferred embodiment, as explained in Nokia GmbH v IPCom GmbH & Co KG [2009] EWHC 3482 (Pat), a principle cited with approval in Optis Cellular Technology LLC v Apple Retail UK Ltd [2022] EWCA Civ 792. Claim 1 was not limited to showers, and even in a shower the relevant purpose extended beyond avoiding scalding to avoiding sudden unexpected changes in temperature, including decreases.
4. The DuElec showers satisfied the risk-of-scalding criterion through the flow stabilisation valve and thermal cut-out, rather than through the design of the diverter valve. Since that criterion was not the correct construction and no alternative criterion was advanced, claims 1 and 4 were not infringed. The issue of infringement by equivalents did not arise.
5. Under section 72(1)(c) of the Patents Act 1977, a claim is insufficient where its boundary is impossible for the skilled person to ascertain. A fuzzy boundary may be acceptable, but an unknowable boundary is not. Applying Anan Kasei Co Ltd v Neo Chemicals & Oxides Ltd [2019] EWCA Civ 1646; [2020] FSR 8, claim 1 was insufficient because the specification supplied no criterion for deciding what degree of flow-rate change was substantial. Claims 4 and 17, which depended on claim 1, were likewise invalid. The grounds concerning excessive claim breadth and obviousness did not arise.

• Court of Appeal (Civil Division): Allowed Norcros’s appeal. The Patent was revoked for insufficiency, and the products did not infringe claims 1 and 4 even if the Patent were valid.
• High Court of Justice, Intellectual Property Enterprise Court: HHJ Melissa Clarke granted Mira relief for infringement by an order dated 9 January 2025, for the reasons given in [2024] EWHC 3247 (IPEC).