Baxi Boiler Duo-Tec Expansion Vessel 8L 5114691 Replacement Part

This baxi duo-tec expansion vessel 8l helps absorb water expansion as your Baxi boiler heats up, keeping system pressure stable. Over time the internal diaphragm can fail, leading to pressure rising quickly when heating, frequent PRV discharge, or pressure dropping after cooling. Replacing the correct vessel restores proper pressure control, reduces nuisance lockouts, and helps protect the system from repeated over-pressure issues.

Compatibility :

• Duo Tec HE: 24, 28, 33
• Duo Tec HE A (Issue 9): 24 (Before/After Serial BTG0815), 28 (Before/After Serial CAC0929)
• Duo Tec Combi ErP: 24 (AC/BC/CC/DC), 28 (AC/BC/CC/DC), 33 (AC/BC/CC/DC), 40 (AC/BC/CC/DC)
• HE System: 15, 18, 24 (Before/After Serial BTF0932), 28 (Before/After Serial CAB1112), 32
• Megaflo HE A: 15, 18, 24, 28, 32
• System ErP (IN): 15 (AC/BC/CC), 18 (AC/BC/CC), 24 (AC/BC/CC), 28 (AC/BC/CC), 32 (AC/BC/CC)
• Combi HE: 24, 28
• Platinum Combi HE: 24, 28, 33, 40
• Platinum Combi HE A: 24 (Before/After Serial BMY0815), 28 (Before/After Serial BNC0932)
• Combi ErP: 24 (CC/DC/EC + IN AC/BC), 28 (CC/DC/EC + IN AC/BC), 33 (CC/DC/EC + IN AC/BC), 40 (CC/DC/EC + IN AC/BC)

Important fitting advice

We recommend that all parts are fitted by a fully qualified Gas Safe registered engineer. If you need help confirming the right part, contact us our team has 10+ years of boiler spares knowledge and friendly chat support to help you quickly.

Delivery

At Boiler Spares Hub, we dispatch orders within 1 working day (Monday-Friday). Orders placed outside working days will be dispatched on the next working day. For delivery options available for this product, please add it to your basket or check our delivery options page.

Returns

We accept 30-day returns. Returns must be in an unopened, sealed box. If we find the item has been used or installation was attempted, we may refuse the return.

Frequently Asked Questions (FAQs)

1. What does the expansion vessel do in a boiler?
It absorbs water expansion when the system heats up, helping keep boiler pressure stable and preventing over-pressure.

2. What are the common symptoms of a failed expansion vessel?
Pressure rises quickly when heating, the PRV/discharge pipe drips outside, frequent re-pressurising, pressure dropping after cooling, and occasional lockouts.

3. How can I quickly check if the expansion vessel might be the issue?
If the pressure jumps up a lot when heating (then drops back down when cooling) or you see regular discharge from the PRV pipe, the vessel may be weak/failed.

4. Will this 8L expansion vessel fit my Baxi Duo-Tec?
It fits the Duo-Tec / Platinum / Baxi models listed in the compatibility section. Match your exact model and any “before/after serial” notes.

5.Does this part come charged with air/nitrogen, or will it need setting?
Expansion vessels are pre-charged, but engineers usually check and set the charge pressure to suit the system before final commissioning.