{"product_id":"flamco-baseflex-heating-expansion-vessel-8l-12l-18l-25l-35l-central-heating-sealed-system","title":"Flamco Baseflex Heating Expansion Vessel 8L 12L 18L 25L 35L — Central Heating Sealed System","description":"\u003cdiv style=\"font-size:16px;font-family:Arial,Helvetica,sans-serif;color:#1a1a1a;max-width:900px;margin:0 auto;line-height:1.6;\"\u003e\n\n  \u003c!-- ── INTRO ─────────────────────────────────────────────────────── --\u003e\n  \u003cp style=\"margin:0 0 18px;\"\u003e\n    The \u003cstrong\u003eFlamco Baseflex\u003c\/strong\u003e is a \u003cstrong\u003eContra-Flex diaphragm heating expansion vessel\u003c\/strong\u003e for sealed central heating and closed-circuit cooling installations — available in \u003cstrong\u003e8L, 12L, 18L, 25L, and 35L\u003c\/strong\u003e capacities (MPNs 25300–25305). As water temperature rises in a sealed system, it expands and must have somewhere to go — the Baseflex temporarily absorbs this expanded volume, maintaining system pressure within safe operating limits and preventing repeated activation of the pressure relief valve. Factory pre-charged to \u003cstrong\u003e1.5 bar\u003c\/strong\u003e. Maximum working pressure \u003cstrong\u003e6 bar\u003c\/strong\u003e; maximum system flow temperature \u003cstrong\u003e120°C\u003c\/strong\u003e. \u003cstrong\u003eEPDM diaphragm\u003c\/strong\u003e, \u003cstrong\u003eall-welded construction\u003c\/strong\u003e with zinc-plated flange, and a durable \u003cstrong\u003ered RAL 3002 epoxy powder-coat\u003c\/strong\u003e finish. Certified to \u003cstrong\u003eEN13831\u003c\/strong\u003e and the Pressure Equipment Directive \u003cstrong\u003e2014\/68\/EU\u003c\/strong\u003e. Compatible with glycol-based antifreeze up to 50% and ethanol-based antifreeze up to 30%. The Flamco Baseflex is one of the most widely specified expansion vessels in UK central heating installations, trusted by heating engineers for its \u003cstrong\u003eContra-Flex clamped diaphragm construction\u003c\/strong\u003e that delivers lower gas permeability and longer service life than standard bladder-type vessels.\n  \u003c\/p\u003e\n\n  \u003c!-- ── RED INSTALLER CALLOUT ──────────────────────────────────── --\u003e\n  \u003cdiv style=\"border-left:4px solid #c0392b;background:#fff5f5;padding:10px 16px;margin-bottom:14px;border-radius:0 6px 6px 0;\"\u003e\n    \u003cstrong style=\"color:#c0392b;\"\u003e⚠ Qualified Installation Required — Pre-Charge Verification Essential\u003c\/strong\u003e — Must be installed by a competent heating engineer in accordance with BS EN 12828 and Building Regulations Part L. \u003cstrong\u003eThe factory pre-charge of 1.5 bar must be verified against the system cold fill pressure before commissioning\u003c\/strong\u003e — the vessel pre-charge should equal the system cold fill pressure. An incorrect pre-charge results in the vessel being waterlogged (pre-charge too low) or providing no useful expansion capacity (pre-charge too high). Check and adjust via the Schrader valve with the vessel isolated and system pressure released.\n  \u003c\/div\u003e\n\n  \u003c!-- ── TEAL SIZING CALLOUT ──────────────────────────────────────── --\u003e\n  \u003cdiv style=\"border-left:4px solid #008377CF;background:#e6f4f3;padding:10px 16px;margin-bottom:22px;border-radius:0 6px 6px 0;\"\u003e\n    \u003cstrong style=\"color:#005c54;\"\u003eℹ Choosing the Right Capacity\u003c\/strong\u003e\u003cbr\u003e\n    Expansion vessel sizing is calculated from the total system water volume, the cold fill pressure, the maximum working pressure, and the maximum system temperature. As a practical guide: an \u003cstrong\u003e8L vessel\u003c\/strong\u003e typically suits small systems up to approximately 100L total water content at standard pressures; \u003cstrong\u003e12L\u003c\/strong\u003e suits systems of 100–150L; \u003cstrong\u003e18L\u003c\/strong\u003e suits 150–250L; \u003cstrong\u003e25L\u003c\/strong\u003e suits 250–350L; and \u003cstrong\u003e35L\u003c\/strong\u003e suits 350–500L — but always confirm with a proper calculation to EN12828 or use a vessel sizing calculator. An undersized vessel will cause the PRV to activate repeatedly; an oversized vessel is not harmful but wastes money.\n  \u003c\/div\u003e\n\n  \u003c!-- ── STAT STRIP ─────────────────────────────────────────────────── --\u003e\n  \u003cdiv style=\"display:flex;flex-wrap:wrap;gap:10px;margin-bottom:20px;\"\u003e\n    \u003cdiv style=\"flex:1;min-width:85px;background:#008377CF;color:#fff;border-radius:6px;padding:11px 8px;text-align:center;\"\u003e\n\u003cdiv style=\"font-size:15px;font-weight:700;\"\u003e8–35 litres\u003c\/div\u003e\n\u003cdiv style=\"font-size:12px;margin-top:3px;\"\u003e5 sizes\u003c\/div\u003e\n\u003c\/div\u003e\n    \u003cdiv style=\"flex:1;min-width:85px;background:#008377CF;color:#fff;border-radius:6px;padding:11px 8px;text-align:center;\"\u003e\n\u003cdiv style=\"font-size:17px;font-weight:700;\"\u003e6 bar\u003c\/div\u003e\n\u003cdiv style=\"font-size:12px;margin-top:3px;\"\u003eMax pressure\u003c\/div\u003e\n\u003c\/div\u003e\n    \u003cdiv style=\"flex:1;min-width:85px;background:#008377CF;color:#fff;border-radius:6px;padding:11px 8px;text-align:center;\"\u003e\n\u003cdiv style=\"font-size:17px;font-weight:700;\"\u003e120°C\u003c\/div\u003e\n\u003cdiv style=\"font-size:12px;margin-top:3px;\"\u003eMax system temp\u003c\/div\u003e\n\u003c\/div\u003e\n    \u003cdiv style=\"flex:1;min-width:85px;background:#008377CF;color:#fff;border-radius:6px;padding:11px 8px;text-align:center;\"\u003e\n\u003cdiv style=\"font-size:17px;font-weight:700;\"\u003eEN13831\u003c\/div\u003e\n\u003cdiv style=\"font-size:12px;margin-top:3px;\"\u003eCertified\u003c\/div\u003e\n\u003c\/div\u003e\n    \u003cdiv style=\"flex:1;min-width:85px;background:#008377CF;color:#fff;border-radius:6px;padding:11px 8px;text-align:center;\"\u003e\n\u003cdiv style=\"font-size:17px;font-weight:700;\"\u003e50% glycol\u003c\/div\u003e\n\u003cdiv style=\"font-size:12px;margin-top:3px;\"\u003eAntifreeze compatible\u003c\/div\u003e\n\u003c\/div\u003e\n  \u003c\/div\u003e\n\n  \u003c!-- ── FEATURES GRID ──────────────────────────────────────────────── --\u003e\n  \u003cdiv style=\"background:#008377CF;color:#fff;font-weight:600;font-size:15px;padding:10px 16px;border-radius:6px 6px 0 0;\"\u003eFeatures \u0026amp; Benefits\u003c\/div\u003e\n  \u003cdiv style=\"display:grid;grid-template-columns:repeat(auto-fill,minmax(255px,1fr));gap:12px;background:#e6f4f3;padding:14px;border-radius:0 0 6px 6px;margin-bottom:22px;\"\u003e\n\n    \u003cdiv style=\"background:#f0faf9;border:1px solid #c8e6e3;border-radius:6px;padding:13px;\"\u003e\n      \u003cdiv style=\"font-weight:700;color:#008377CF;margin-bottom:5px;\"\u003e✔ Contra-Flex Clamped Diaphragm — Lower Gas Permeability\u003c\/div\u003e\n      \u003cdiv style=\"font-size:14px;\"\u003eThe Baseflex uses Flamco's \u003cstrong\u003eContra-Flex clamped diaphragm design\u003c\/strong\u003e, where the EPDM diaphragm is mechanically clamped between two vessel halves with a clamp ring, rather than simply floating as a bladder inside the vessel. This clamping arrangement \u003cstrong\u003ehalves the air-to-water surface area ratio\u003c\/strong\u003e compared to conventional bladder vessels — significantly reducing the rate at which the nitrogen or air pre-charge permeates through the diaphragm over time. The result is a vessel that maintains its pre-charge pressure far longer between service checks, a more reliable and extended service life, and reduced risk of the vessel becoming waterlogged prematurely.\u003c\/div\u003e\n    \u003c\/div\u003e\n\n    \u003cdiv style=\"background:#f0faf9;border:1px solid #c8e6e3;border-radius:6px;padding:13px;\"\u003e\n      \u003cdiv style=\"font-weight:700;color:#008377CF;margin-bottom:5px;\"\u003e✔ All-Welded Construction — Factory Tested\u003c\/div\u003e\n      \u003cdiv style=\"font-size:14px;\"\u003eThe Baseflex shell is \u003cstrong\u003eall-welded steel construction\u003c\/strong\u003e — there are no bolted flanges or mechanical seams that could work loose over years of pressure cycling. The zinc-plated flange at the connection provides a corrosion-resistant joint face. \u003cstrong\u003eEvery vessel is factory tested before shipment\u003c\/strong\u003e to confirm structural integrity and correct pre-charge pressure — reducing the risk of receiving a vessel with an incorrect pre-charge or a manufacturing defect. The stove-enamelled outer casing in red RAL 3002 provides corrosion protection for plant room and airing cupboard installations.\u003c\/div\u003e\n    \u003c\/div\u003e\n\n    \u003cdiv style=\"background:#f0faf9;border:1px solid #c8e6e3;border-radius:6px;padding:13px;\"\u003e\n      \u003cdiv style=\"font-weight:700;color:#008377CF;margin-bottom:5px;\"\u003e✔ EPDM Diaphragm — 120°C System \/ 70°C Diaphragm\u003c\/div\u003e\n      \u003cdiv style=\"font-size:14px;\"\u003e\n\u003cstrong\u003eEPDM (Ethylene Propylene Diene Monomer) rubber\u003c\/strong\u003e is the optimal diaphragm material for heating expansion vessels — it has excellent resistance to hot water, steam, and the inhibitor chemicals used in modern sealed systems, and remains flexible across the operating temperature range without the cracking that affects inferior rubber compounds. The diaphragm is rated to a continuous maximum temperature of \u003cstrong\u003e70°C\u003c\/strong\u003e (and down to –10°C), while the system itself can operate at up to 120°C — the diaphragm temperature is lower than the system temperature because it is protected from direct contact with the hottest system water.\u003c\/div\u003e\n    \u003c\/div\u003e\n\n    \u003cdiv style=\"background:#f0faf9;border:1px solid #c8e6e3;border-radius:6px;padding:13px;\"\u003e\n      \u003cdiv style=\"font-weight:700;color:#008377CF;margin-bottom:5px;\"\u003e✔ Glycol \u0026amp; Ethanol Antifreeze Compatible\u003c\/div\u003e\n      \u003cdiv style=\"font-size:14px;\"\u003eThe Baseflex is approved for use with systems containing \u003cstrong\u003eglycol-based antifreeze up to 50% concentration\u003c\/strong\u003e (such as Fernox Antifreeze Protector or similar propylene\/ethylene glycol inhibitor fluids) and \u003cstrong\u003eethanol-based antifreeze up to 30%\u003c\/strong\u003e. This makes the Baseflex suitable for \u003cstrong\u003esolar thermal primary circuits, heat pump systems with frost protection requirements, and any installation where antifreeze is specified\u003c\/strong\u003e. Many competing expansion vessels are not rated for glycol use, limiting their application in solar and heat pump systems. Confirm the specific antifreeze brand and concentration with Flamco if outside these standard ranges.\u003c\/div\u003e\n    \u003c\/div\u003e\n\n    \u003cdiv style=\"background:#f0faf9;border:1px solid #c8e6e3;border-radius:6px;padding:13px;\"\u003e\n      \u003cdiv style=\"font-weight:700;color:#008377CF;margin-bottom:5px;\"\u003e✔ 35L Model — Standard Legs Fitted\u003c\/div\u003e\n      \u003cdiv style=\"font-size:14px;\"\u003eThe 35L Baseflex (MPN 25305) is factory-fitted with \u003cstrong\u003estandard support legs\u003c\/strong\u003e as part of the unit — this is standard across the Flamco Baseflex 35–80L range. The legs allow the vessel to stand unsupported on a plant room or airing cupboard floor during installation and positioning, making it easier to locate and connect without an installer needing to support the vessel weight while making plumbing connections. The 8L–25L models (25300–25303) are wall-mounted or pipework-supported via their ¾\" connection without requiring separate legs.\u003c\/div\u003e\n    \u003c\/div\u003e\n\n    \u003cdiv style=\"background:#f0faf9;border:1px solid #c8e6e3;border-radius:6px;padding:13px;\"\u003e\n      \u003cdiv style=\"font-weight:700;color:#008377CF;margin-bottom:5px;\"\u003e✔ EN13831 \u0026amp; PED 2014\/68\/EU — White Finish Option\u003c\/div\u003e\n      \u003cdiv style=\"font-size:14px;\"\u003eCertification to \u003cstrong\u003eEN13831\u003c\/strong\u003e (the European harmonised standard for closed expansion vessels) and the \u003cstrong\u003ePressure Equipment Directive 2014\/68\/EU\u003c\/strong\u003e (UK CA post-Brexit) provides the compliance documentation required for installation in systems subject to Building Regulations notification and for commercial and insurance purposes. The standard red RAL 3002 powder coat finish can be specified in \u003cstrong\u003ewhite RAL 9010\u003c\/strong\u003e as an alternative — suitable for visible or aesthetic installations where the red finish is not desired. Both finishes are the same durable epoxy powder coat.\u003c\/div\u003e\n    \u003c\/div\u003e\n\n  \u003c\/div\u003e\n\n  \u003c!-- ── VARIANT TABLE ──────────────────────────────────────────────── --\u003e\n  \u003cdiv style=\"background:#008377CF;color:#fff;font-weight:600;font-size:15px;padding:10px 16px;border-radius:6px 6px 0 0;\"\u003eModel Range — MPN 25300 to 25305\u003c\/div\u003e\n  \u003cdiv style=\"overflow-x:auto;margin-bottom:22px;\"\u003e\n  \u003ctable style=\"width:100%;border-collapse:collapse;font-size:14px;min-width:540px;\"\u003e\n    \u003cthead\u003e\n      \u003ctr style=\"background:#005c54;color:#fff;\"\u003e\n        \u003cth style=\"padding:9px 10px;text-align:left;font-weight:600;border-bottom:2px solid #008377CF;\"\u003eMPN\u003c\/th\u003e\n        \u003cth style=\"padding:9px 10px;text-align:center;font-weight:600;border-bottom:2px solid #008377CF;\"\u003eModel\u003c\/th\u003e\n        \u003cth style=\"padding:9px 10px;text-align:center;font-weight:600;border-bottom:2px solid #008377CF;\"\u003eCapacity\u003c\/th\u003e\n        \u003cth style=\"padding:9px 10px;text-align:center;font-weight:600;border-bottom:2px solid #008377CF;\"\u003ePre-charge\u003c\/th\u003e\n        \u003cth style=\"padding:9px 10px;text-align:center;font-weight:600;border-bottom:2px solid #008377CF;\"\u003eMax Pressure\u003c\/th\u003e\n        \u003cth style=\"padding:9px 10px;text-align:center;font-weight:600;border-bottom:2px solid #008377CF;\"\u003eNotes\u003c\/th\u003e\n      \u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr style=\"background:#f0faf9;\"\u003e\n        \u003ctd style=\"padding:8px 10px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003e25300\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003eBaseflex 8\/1.5\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e\u003cstrong\u003e8L\u003c\/strong\u003e\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e1.5 bar\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e6 bar\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;border-bottom:1px solid #c8e6e3;\"\u003eG ¾\" M · wall\/pipe mount\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr style=\"background:#fff;\"\u003e\n        \u003ctd style=\"padding:8px 10px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003e25301\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003eBaseflex 12\/1.5\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e\u003cstrong\u003e12L\u003c\/strong\u003e\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e1.5 bar\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e6 bar\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;border-bottom:1px solid #c8e6e3;\"\u003eG ¾\" M · wall\/pipe mount\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr style=\"background:#f0faf9;\"\u003e\n        \u003ctd style=\"padding:8px 10px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003e25302\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003eBaseflex 18\/1.5\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e\u003cstrong\u003e18L\u003c\/strong\u003e\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e1.5 bar\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e6 bar\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;border-bottom:1px solid #c8e6e3;\"\u003eG ¾\" M · wall\/pipe mount\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr style=\"background:#fff;\"\u003e\n        \u003ctd style=\"padding:8px 10px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003e25303\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003eBaseflex 25\/1.5\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e\u003cstrong\u003e25L\u003c\/strong\u003e\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e1.5 bar\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e6 bar\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;border-bottom:1px solid #c8e6e3;\"\u003eG ¾\" M · Ø290 × H463mm · 4.0kg\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr style=\"background:#f0faf9;\"\u003e\n        \u003ctd style=\"padding:8px 10px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003e25305\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003eBaseflex 35\/1.5\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e\u003cstrong\u003e35L\u003c\/strong\u003e\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e1.5 bar\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;text-align:center;border-bottom:1px solid #c8e6e3;\"\u003e6 bar\u003c\/td\u003e\n        \u003ctd style=\"padding:8px 10px;border-bottom:1px solid #c8e6e3;\"\u003eG ¾\" M · legs fitted as standard\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n  \u003c\/div\u003e\n\n  \u003c!-- ── SHARED SPEC TABLE ──────────────────────────────────────────── --\u003e\n  \u003cdiv style=\"background:#008377CF;color:#fff;font-weight:600;font-size:15px;padding:10px 16px;border-radius:6px 6px 0 0;\"\u003eTechnical Specifications — All Models (Common)\u003c\/div\u003e\n  \u003ctable style=\"width:100%;border-collapse:collapse;margin-bottom:22px;font-size:14px;\"\u003e\n    \u003ctbody\u003e\n      \u003ctr style=\"background:#f0faf9;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;width:44%;border-bottom:1px solid #c8e6e3;\"\u003eManufacturer \/ Range\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003eFlamco — \u003cstrong\u003eBaseflex\u003c\/strong\u003e\n\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#fff;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003eFactory Pre-charge\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003e\n\u003cstrong\u003e1.5 bar\u003c\/strong\u003e (adjustable via Schrader valve)\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#f0faf9;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003eMax. Working Pressure\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003e\u003cstrong\u003e6 bar\u003c\/strong\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#fff;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003eMax. System Flow Temperature\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003e\u003cstrong\u003e120°C\u003c\/strong\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#f0faf9;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003eDiaphragm Material\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003eEPDM\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#fff;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003eDiaphragm Temperature Range\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003e–10°C to +70°C (continuous)\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#f0faf9;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003eDiaphragm Design\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003eContra-Flex — clamped between two vessel halves (clamp ring)\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#fff;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003eConstruction\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003eAll welded · zinc-plated flange\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#f0faf9;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003eOuter Finish\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003eRed RAL 3002 epoxy powder coat (white RAL 9010 available)\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#fff;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003eSystem Connection\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003eG ¾\" male BSP — all models\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#f0faf9;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003eAntifreeze Compatibility\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003eGlycol-based up to 50% · Ethanol-based up to 30%\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#fff;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003eApplication\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003eSealed heating (EN12828) · closed cooling · solar thermal primary\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#f0faf9;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;border-bottom:1px solid #c8e6e3;\"\u003eQuality \/ Testing\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #c8e6e3;\"\u003eFactory tested before shipment\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr style=\"background:#fff;\"\u003e\n\u003ctd style=\"padding:9px 14px;font-weight:600;\"\u003eCertifications\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;\"\u003eEN13831 · PED 2014\/68\/EU\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\n  \u003c!-- ── FAQ ────────────────────────────────────────────────────────── --\u003e\n  \u003cdiv style=\"background:#008377CF;color:#fff;font-weight:600;font-size:15px;padding:10px 16px;border-radius:6px 6px 0 0;\"\u003eFrequently Asked Questions\u003c\/div\u003e\n  \u003cdiv style=\"border:1px solid #c8e6e3;border-top:none;border-radius:0 0 6px 6px;margin-bottom:8px;\"\u003e\n\n    \u003cdetails style=\"border-bottom:1px solid #c8e6e3;\"\u003e\n      \u003csummary style=\"padding:13px 16px;cursor:pointer;font-weight:600;background:#f0faf9;\"\u003eHow do I know if my expansion vessel has failed?\u003c\/summary\u003e\n      \u003cdiv style=\"padding:11px 16px;font-size:14px;\"\u003eThe most reliable sign is the \u003cstrong\u003epressure relief valve repeatedly releasing small amounts of water\u003c\/strong\u003e — this means the vessel can no longer absorb expansion. To confirm: with the system cold and at its fill pressure, attach a tyre gauge to the vessel Schrader valve. A healthy vessel will show the pre-charge pressure (typically 1.0–1.5 bar). If the reading is zero or water comes out, the diaphragm has failed. Another test: tap the vessel — a healthy vessel sounds partly hollow; a waterlogged vessel sounds solid throughout. Vessels should also be checked annually as part of a boiler service; most last 10–15 years with correct installation and pre-charge, but may fail sooner in hard water or high-cycling systems.\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails style=\"border-bottom:1px solid #c8e6e3;\"\u003e\n      \u003csummary style=\"padding:13px 16px;cursor:pointer;font-weight:600;background:#fff;\"\u003eWhat is the correct pre-charge pressure for my system?\u003c\/summary\u003e\n      \u003cdiv style=\"padding:11px 16px;font-size:14px;\"\u003eThe vessel pre-charge pressure should be set to \u003cstrong\u003ematch the system's cold static fill pressure\u003c\/strong\u003e — the pressure at the vessel location when the system is cold and fully charged but before the boiler has been running. For most domestic systems this is 0.5–1.5 bar depending on the height of the system above the vessel, the incoming mains pressure, and whether a filling loop or pressurisation unit is used. The factory 1.5 bar pre-charge suits many typical installations, but it must be checked and adjusted on site. To adjust: isolate the vessel, drain the system side of the vessel to zero, check the gas charge with a tyre gauge, and inflate or deflate to the correct value before reconnecting.\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails style=\"border-bottom:1px solid #c8e6e3;\"\u003e\n      \u003csummary style=\"padding:13px 16px;cursor:pointer;font-weight:600;background:#f0faf9;\"\u003eCan I use this vessel on a solar thermal primary circuit?\u003c\/summary\u003e\n      \u003cdiv style=\"padding:11px 16px;font-size:14px;\"\u003eYes — the Flamco Baseflex is suitable for solar thermal primary circuits with the following considerations: the \u003cstrong\u003eEPDM diaphragm is compatible with glycol-based solar antifreeze up to 50% concentration\u003c\/strong\u003e, which covers the standard propylene glycol solutions used in UK solar thermal systems. The maximum system temperature of 120°C accommodates stagnation temperatures in typical evacuated tube and flat-plate collectors. However, on solar thermal systems the maximum temperature can be higher during stagnation (up to 150–200°C in the collector) — the expansion vessel should be located on the return (cooler) side of the circuit, away from direct stagnation temperatures, with a connecting pipe of sufficient length to limit vessel temperature. Consult the solar system designer for final specification.\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails style=\"border-bottom:1px solid #c8e6e3;\"\u003e\n      \u003csummary style=\"padding:13px 16px;cursor:pointer;font-weight:600;background:#fff;\"\u003eWhat is the difference between the Baseflex and a standard bladder expansion vessel?\u003c\/summary\u003e\n      \u003cdiv style=\"padding:11px 16px;font-size:14px;\"\u003eA standard bladder expansion vessel uses a \u003cstrong\u003efree-floating rubber bladder\u003c\/strong\u003e inside the vessel shell. The entire outer surface of the bladder is exposed to the gas charge, giving a large gas-to-water interface area through which gas can permeate over time — causing the vessel to gradually lose its pre-charge. The Flamco \u003cstrong\u003eContra-Flex clamped design\u003c\/strong\u003e clamps the diaphragm between the two vessel halves, so only the inner surface of the diaphragm faces the water. The gas charge is on the outer side. This reduces the gas-to-water diaphragm surface area by approximately half, dramatically reducing the permeation rate and extending the time between pre-charge top-ups. In practice, a well-installed Baseflex will maintain its pre-charge for significantly longer than a standard bladder vessel of the same size.\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary style=\"padding:13px 16px;cursor:pointer;font-weight:600;background:#f0faf9;\"\u003eCan I use the Baseflex on an open-vented system?\u003c\/summary\u003e\n      \u003cdiv style=\"padding:11px 16px;font-size:14px;\"\u003e\n\u003cstrong\u003eNo\u003c\/strong\u003e — the Flamco Baseflex is designed for \u003cstrong\u003esealed (closed) systems only\u003c\/strong\u003e. Open-vented systems manage expansion via a feed and expansion tank in the loft that is open to atmosphere — they do not use expansion vessels. The Baseflex is for \u003cstrong\u003esealed heating systems\u003c\/strong\u003e (as described in EN12828) and closed cooling circuits where the system is pressurised and relies on the expansion vessel to accommodate water volume changes. If you are converting an existing open-vented system to sealed, the open-vent and feed pipes must be correctly removed or capped, a filling loop and pressure gauge added, and a correctly-sized expansion vessel like the Baseflex installed — this is a significant system modification that should be designed and installed by a qualified heating engineer.\u003c\/div\u003e\n    \u003c\/details\u003e\n\n  \u003c\/div\u003e\n\n\u003c\/div\u003e","brand":"Flamco","offers":[{"title":"8L","offer_id":64260734845277,"sku":"25300","price":35.0,"currency_code":"GBP","in_stock":true},{"title":"12L","offer_id":64260734878045,"sku":"25301","price":37.0,"currency_code":"GBP","in_stock":true},{"title":"18L","offer_id":64260734910813,"sku":"25302","price":39.0,"currency_code":"GBP","in_stock":true},{"title":"25L","offer_id":64260734943581,"sku":"25303","price":43.0,"currency_code":"GBP","in_stock":true},{"title":"35L","offer_id":64260734976349,"sku":"25305","price":55.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0958\/2051\/3629\/files\/FlamcoBaseflexHeatingExpansionVesselInside.webp?v=1776686327","url":"https:\/\/qualityheating.co.uk\/products\/flamco-baseflex-heating-expansion-vessel-8l-12l-18l-25l-35l-central-heating-sealed-system","provider":"AIZO Quality Heating","version":"1.0","type":"link"}