Cylindrical heating expansion vessel
The vessel is supplied pre-charged with nitrogen, but the pre-charge has to match the static pressure of the system it is fitted to. The installer checks and adjusts it with the water side at zero pressure before the circuit is filled; a wrong pre-charge reduces the usable volume of the vessel.
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Description and application
The cylindrical heating expansion vessel from the THERMALINO Eternal line absorbs the expansion of water in sealed central heating systems and keeps system pressure stable as the water heats and cools. It has a replaceable EPDM membrane and a nitrogen pre-charge, is made to EN 13831 for a maximum operating pressure of 10 bar, and comes in sizes from 2 to 50 litres for wall mounting.
The Eternal line cylindrical heating expansion vessel takes up the extra volume of water that forms as a sealed heating circuit warms up, and gives it back as the system cools. Without this space, system pressure would rise towards the safety valve setting on every heating cycle. The vessel is wall mounted, finished in red and available in 2, 5, 8, 12, 18, 24, 35 and 50 litre sizes, from a small boiler circuit to larger radiator and underfloor systems. Inside, a high-quality EPDM membrane of Italian origin separates the system water from a nitrogen gas cushion. The membrane is replaceable, so when it wears it can be renewed by an installer without replacing the whole vessel. The vessel is made to EN 13831, the European standard for closed expansion vessels with a built-in diaphragm, and is rated for a maximum operating pressure of 10 bar. It is supplied pre-charged with nitrogen. Before the system is filled, the installer checks the pre-charge and sets it to the static pressure of the installation, then connects the vessel to the heating circuit, usually on the return side near the boiler. Alongside the standard connection, it can be supplied with other connection sizes on request, which makes it straightforward to use as a replacement central heating expansion vessel or as the expansion vessel for a boiler being installed or serviced. The right size depends on the water volume of the system, its maximum flow temperature, the static head and the safety valve setting. Dimensions and connection details for each size are given in the technical data sheet.
- Sealed central heating systems with wall-hung and floor-standing boilers
- Replacement vessels during boiler service and repair
- Radiator and underfloor heating circuits
- Heat pump heating circuits, sized to the system volume and temperatures
- Houses, apartments and residential blocks
- Offices, shops, hotels and schools with closed heating systems, sized to the system volume
Technical summary
- SKU
- THL-E-EXV-0001
- Origin
- Made in Türkiye
- Size range
- 2 L – 50 L
- Application
- Heating
- Membrane
- EPDM
- Membrane type
- Replaceable
- Max. operating pressure
- 10 bar
- Mounting
- Wall
- Standard
- EN 13831
Questions
- How do I size a heating expansion vessel for a sealed central heating system with radiators and a wall-hung boiler?
- A heating expansion vessel is sized from the total water volume of the system, the maximum flow temperature, the static head above the vessel and the safety valve setting. Rules of thumb based on the number of radiators or the boiler output give only a starting point, because they ignore static head and pre-charge; calculate the expansion volume and choose the next size up. The Eternal line vessel comes in 2, 5, 8, 12, 18, 24, 35 and 50 litre sizes, so the calculated volume can be matched closely, and an undersized vessel should always be avoided.
- Does the pre-charge of a heating expansion vessel have to be checked with the heating system drained or isolated from water pressure?
- Yes, the pre-charge of a heating expansion vessel can only be read correctly when the water side is at zero pressure, either by isolating the vessel or by draining the system down. With water pressure still on the membrane, the gauge shows system pressure rather than the gas charge. Checking and recharging a vessel on a pressurised system is work for a qualified heating installer, who sets the pre-charge to the static pressure of the installation and refills and vents the system afterwards.
- What are the symptoms of a faulty expansion vessel on a domestic central heating boiler?
- A faulty expansion vessel usually shows as boiler pressure that climbs sharply when the heating runs and falls back when it is off, a safety valve that drips or discharges, and a system that needs topping up more often than before. The cause is either loss of the gas pre-charge or a damaged membrane that lets water into the gas side. If you notice these signs, have a qualified heating installer check the vessel; do not try to recharge or open it yourself.
- What happens to a sealed heating system when the boiler expansion tank goes bad and loses its gas cushion?
- When a boiler expansion tank loses its gas cushion, the expanding water has nowhere to go, so system pressure rises on every heating cycle until the safety valve opens. Each discharge removes water from the circuit, the pressure then drops when the system cools, and the boiler may lock out on low or high pressure. Repeated cycling also stresses valves, joints and the boiler itself, so the vessel should be inspected by a qualified installer as soon as the pattern appears.
- What is the lifespan of a heating expansion vessel in a home heating system, and can its membrane be replaced instead of the whole vessel?
- The lifespan of a heating expansion vessel depends mainly on correct sizing, a correctly set pre-charge and regular checks, because an undersized or wrongly charged vessel overworks its membrane. The Eternal line vessel has a replaceable EPDM membrane, so a worn membrane can be renewed by a qualified installer without replacing the vessel body. Having the pre-charge checked at the annual boiler service helps the vessel keep working as intended.
Range
| Size | Red | Variant codes |
|---|---|---|
| 2 L✓ Red | ✓ | |
| 5 L✓ Red | ✓ | |
| 8 L✓ Red | ✓ | |
| 12 L✓ Red | ✓ | |
| 18 L✓ Red | ✓ | |
| 24 L✓ Red | ✓ | |
| 35 L✓ Red | ✓ | |
| 50 L✓ Red | ✓ |
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This product is listed under Heating Expansion Vessels.
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