A heat pump typically runs a small temperature difference and a higher flow rate than a boiler. The stored water still has to reach a usable hot-water temperature, so the coil needs enough surface area to transfer that heat. That is the same point as what makes a cylinder compatible with a heat pump: a conventional boiler coil is sized around a much larger temperature difference.
Ask a qualified installer to match the cylinder to the heat generator, not just the bath count. Figures below are from Vaillant UK sources as of October 2026. See also the Vaillant pages on this site.
Original hub comparison
Table from hub page 18612. The 1.8 m² / 2.6 m² / “40% more” claims are not in current Vaillant UK datasheets — see the corrections after the table.
| Model type | Coil area (m²) | Compared with Standard |
|---|---|---|
| uniSTOR Standard | 1.8 | — |
| uniSTOR plus (internal expansion) | 2.6 | 40% more |
| uniSTOR pure (external expansion) | 2.6 | 40% more |
Even on those hub numbers, 2.6 versus 1.8 is 44% more, not 40% ((2.6 − 1.8) / 1.8).
Vaillant UK’s current plus and pure range does not use “Standard” as a third coil variant. Plus and pure of the same size share the same heat exchanger; the difference is internal expansion (plus) versus an external vessel (pure). Coil size varies with cylinder volume, not with plus versus pure.
Current plus/pure installation manuals list heat-exchanger volume, not a single 1.8 or 2.6 m² surface area. A Vaillant UK merchant note (February 2025) gives slimline high-recovery coils as up to 2.4 m². We have not found the hub’s 1.8 or 2.6 m² figures on vaillant.co.uk datasheets checked in October 2026, so they are not treated as current specification.
Current UK naming (plus, pure, “standard”)
Vaillant UK’s current high-recovery range is uniSTOR plus and uniSTOR pure (product generation VIH RW …/5). They are sold for Vaillant heat pumps and system boilers. Slimline (490 mm) launched in 2025; standard-diameter (580 mm) followed the same year, covering 150–300 L.
On those pages, “standard” means unplumbed (versus pre-plumbed) or standard diameter (versus slimline). It is not a separate coil family called uniSTOR Standard.
The consumer site still lists an older uniSTOR hot water cylinder for system and regular boilers (120–300 L) and a separate uniSTOR heat pump cylinder (150–800 L). Those are not discontinued as a whole. Pre-plumbed boiler-only cylinders were phased down from April 2025 as plus/pure took over high-recovery stock. Plus and pure are the heat-pump-capable replacement range, not a heat-pump-only dead end.
plus / pure heat-exchanger volume by size
From Vaillant UK installation instructions 8000014621-07. Plus and pure of the same size have the same coil volume.
| Size | Diameter | Heat-exchanger volume |
|---|---|---|
| Slimline 90, 150, 175 L | 490 mm | 7.62 L |
| Slimline 210 L | 490 mm | 9.93 L |
| Standard 150, 175 L | 580 mm | 7.82 L |
| Standard 210, 250, 300 L | 580 mm | 10.78 L |
Verified coil surface areas (earlier UK datasheets)
These m² figures are published on Vaillant UK professional datasheets for the previous boiler and heat-pump uniSTOR generations. They are not plus/pure /5 values.
| Range | Size | Coil area (m²) |
|---|---|---|
| Boiler uniSTOR (VIH GB …/3) | 120–150 L | 0.69 |
| Boiler uniSTOR (VIH GB …/3) | 180–300 L | 0.80 |
| Heat-pump uniSTOR (VIH RW GB) | 150 L (incl. slimline) | 1.0 |
| Heat-pump uniSTOR (VIH RW GB) | 200 L | 1.4 |
| Heat-pump uniSTOR (VIH RW GB) | 250 L | 2.4 |
| Heat-pump uniSTOR (VIH RW GB) | 300 L | 2.8 |
| Heat-pump uniSTOR | 500 L / 800 L | 4.7 / 7.0 |
Compared with a 0.80 m² boiler coil, the 2.4 m² heat-pump coil on the 250 L model is three times the area — a much larger step than the hub’s “40% more”. Spec the actual size; do not treat one m² figure as the whole range.
Sources
Checked October 2026. Use the current datasheet for the article number on the job.
- uniSTOR plus & pure slimline (professional.vaillant.co.uk)
- uniSTOR plus & pure standard diameter (professional.vaillant.co.uk)
- uniSTOR plus/pure installation instructions 8000014621-07 (PDF)
- uniSTOR hot water cylinder (vaillant.co.uk)
- uniSTOR heat pump cylinder (vaillant.co.uk)
- uniSTOR boiler cylinder instructions — 0.69 / 0.80 m² (PDF)
- uniSTOR HP instructions — 1.0 / 1.4 / 2.4 / 2.8 m² (PDF)
- Vaillant heat pump cylinder brochure 2024 (PDF)
Related
- What makes a cylinder compatible with a heat pump
- Retrofit an existing cylinder for a heat pump
- Vaillant
- Heat pumps
Migrated from hub.myboiler.com page 18612. Guidance only. Cylinder selection and commissioning should be done by a qualified installer using the current Vaillant datasheet for the exact model.