Zilmet OEM-PRO 8 Liter 1/2" Combi Boiler Expansion Vessel (Ø390 × H81) – Buderus, Biasi, Ferroli Compatible

This is the Zilmet equivalent of the 8-liter round expansion vessel with 1/2" connection used in Buderus, Biasi and Ferroli combi boilers. Part of the Italian brand Zilmet’s OEM-PRO series, this vessel absorbs the expansion of heated system water and balances system pressure; this prevents the safety relief valve from constantly discharging water, the pressure gauge from rising into the red zone and the boiler from showing a pressure fault. Its flat round body shape (Ø390 × H81 mm) is made for models where it sits horizontally inside the boiler casing.

Original Zilmet Expansion Vessel Compatible with Buderus, Biasi and Ferroli Boilers

• Brand / Series: Zilmet / Drawing 521 – Family 13C OEM-PRO
• Yedepa Product Code: ZLM30-R
• Equivalent / Original Codes: Buderus 76089201 · Bosch 87167458880 · 8716142502-1
• Nominal Volume: 8 liters
• Connection: 1/2" G thread (male), on the 180° axis
• Dimensions: Diameter Ø390 mm · Height 81 mm
• Maximum Working Pressure (P max): 3 bar
• Pre-charge Pressure (Precharge): 1 bar
• Maximum Operating Temperature (T max): 90°C
• Body: Steel, red baked paint; pre-charge check valve (Schrader valve) on top

Technical Specifications, Equivalent Codes and Installation Warnings

• Not for use in drinking water installations. As also stated on the product label, this vessel is for closed-circuit heating systems; do not fit it to a booster pump or potable water line.
• Measure the pre-charge pressure before installation. The vessel comes with a 1 bar pre-charge; if the system fill pressure is different, adjust it at the valve. Measurement and adjustment must always be done with the water side of the vessel empty.
• Fault diagnosis: If the boiler frequently loses pressure, the safety relief valve discharges water when hot, or the pressure gauge rises quickly while running and drops when cool, the expansion vessel is not doing its job. If water comes out of the valve instead of air, the membrane is punctured; the vessel must be replaced.
• Size and connection check: Before ordering, compare the diameter (Ø390 mm), height (81 mm) and connection size (1/2") of the vessel you will remove. Even on boilers of the same brand, the vessel shape may change with series/production year.
• Do not strain the vessel body when tightening the fitting, do not skip replacing the seal, and check for leaks after installation with the system under pressure. When installing inside the boiler, refit the anti-vibration pads.
• For membrane life, a pre-charge check every six months is recommended; the correct pre-charge extends the life of both the vessel and the boiler pump.