The Vaillant ecoTEC Plus 424 (MPN 10021223) is a 24kW open vent (regular/heat-only) gas boiler, designed for homes running a traditional open-vented system with a hot water cylinder and a cold water storage tank in the loft. It's built for households with higher, more consistent hot water demand across two or more bathrooms, where an open vent system's steady pressure delivery suits the property better than a combi.
One of the most compact open vent boilers Vaillant has developed, the 424 is hand-built at Vaillant's Derbyshire manufacturing plant and comes with a 5-year guarantee out of the box, extendable to 10 years when registered with Vaillant Advance and fitted with a boiler protection kit. A rear flue option and push-fit flue system give installers flexibility to site the boiler in more locations than a top-flue-only design allows.
10 Yrs
Warranty (Advance)
Gas Safe installation required. This is a mains gas appliance and must be installed, commissioned and serviced by a Gas Safe registered engineer, in line with Building Regulations Part L and current Gas Safety (Installation and Use) Regulations.
Boiler-only, open vent system required: This is a heat-only (regular) boiler, not a combi or system boiler. It must be installed with an existing or new open-vented cylinder and cold water storage tank — it will not work as a standalone unit and does not provide instant mains-pressure hot water on its own.
Compact, Lightweight Design
At 602 × 375 × 320mm and 23kg, it's one of the most compact open vent boilers Vaillant has built, giving installers excellent siting flexibility including standard kitchen cupboards.
Rear Flue Option
A rear flue outlet is available alongside the standard top flue, letting the boiler be installed in situations where a top exit isn't practical.
Wide Modulation Range
A 1:4.9 modulation ratio lets the boiler closely match output to demand, reducing cycling and improving overall energy efficiency compared with a narrower-range appliance.
Built-In Frost Protection
Two-stage frost protection is built in as standard, keeping the boiler safely operational through cold snaps without extra components.
Large Backlit Display
A large backlit plain-text display gives clear visibility of boiler status and fault codes even in poor lighting, with push-button programming for straightforward day-to-day use.
Easy Access Servicing
Removable side panels give installers and engineers straightforward access during installation, routine maintenance and repair work.
Heating Performance
Nominal Heat Output (50/30°C, condensing)
6.3–25.7 kW
Nominal Heat Output (80/60°C, non-condensing)
6.1–24.6 kW
Flow Temperature Range
10–80°C
Flow Temperature Factory Setting
75°C
Water Generation
Maximum Heat Output for Water Generation
30 kW
Approximate Condensate Volume (50/30°C)
2.47 litres/hr
Physical & Connections
Dimensions (H × W × D)
602 × 375 × 320 mm
Boiler Lift Weight (dry)
23.0 kg
Gas Inlet Connection
15mm
Heating Flow & Return Connections
22mm
Heat Exchanger Material
Aluminium
Emissions & Noise
NOx Emissions (EN 15502-2-1)
39 mg/kWh
Flueing Options
Max Horizontal Flue (60/100)
10 m
Max Vertical Flue (60/100)
10 m
Max Horizontal Flue (80/125)
25 m
Max Vertical Flue (80/125)
25 m
Compliance & Coverage
Manufacturer Part Number (MPN)
0010021223
Gas Council Number
41-694-16
Warranty
5 years standard; 10 years with Vaillant Advance registration and boiler protection kit
What's the difference between an open vent boiler and a combi boiler?
An open vent (regular) boiler only heats water — it needs a separate hot water cylinder and a cold water storage tank, typically in the loft, to store and deliver hot water. A combi boiler heats water on demand with no cylinder needed. Open vent systems suit homes with higher simultaneous hot water demand across multiple bathrooms, since output isn't limited by mains flow rate.
Do I need a cylinder and tank to use this boiler?
Yes. This is a heat-only boiler supplied without a cylinder — it must be connected to an existing or new open-vented hot water cylinder and a cold water storage tank to provide domestic hot water. It cannot function as a standalone unit.
How do I get the full 10-year warranty?
The boiler ships with a 5-year guarantee out of the box. To extend this to 10 years, it must be registered with Vaillant Advance and fitted with a compatible boiler protection kit at installation — confirm current eligibility and registration steps with Vaillant before completing the install.
Can the flue exit through the rear instead of the top?
Yes. The ecoTEC Plus 424 supports a rear flue option in addition to the standard top flue, giving installers more flexibility when siting the boiler in properties where a top exit isn't practical.
Who can install this boiler?
Installation, commissioning and servicing must be carried out by a Gas Safe registered engineer, in line with UK Gas Safety (Installation and Use) Regulations and Building Regulations Part L.
