Vaillant Heat Exchanger Dhw 20 17-8973 178973

Vaillant Heat Exchanger Dhw 20 17-8973 178973

The Vaillant DHW Heat Exchanger (Part No. 178973), often referred to as a "Secondary" or "Plate" heat exchanger, is the component responsible for transferring heat from the boiler's primary heating water to your domestic hot water (taps and showers). This genuine OEM part features a 20-plate design, providing a large surface area for rapid and efficient heat transfer. It is a critical replacement part for restoring hot water performance in Vaillant ecoTEC combi boilers.

This part is also commonly identified by the reference 17-8973.

Key Features and Specifications
20-Plate High Efficiency: Constructed from high-grade stainless steel plates brazed together to maximize thermal conductivity and withstand high system pressures.

Instant Hot Water: Designed to deliver the flow rates required for modern multi-outlet homes, ensuring consistent water temperatures.

Genuine Vaillant Part: Manufactured to the exact dimensions and pressure ratings required for Vaillant hydraulic blocks, ensuring a perfect, leak-free fit.

Durable Construction: Resistant to corrosion and thermal stress, ensuring a long operational life when used with properly treated system water.

Direct Replacement: Replaces older or scaled-up 20-plate heat exchangers found in the ecoTEC range.

Boiler Compatibility
This 20-plate heat exchanger is the standard fitment for many 24kW and 28kW Vaillant combi boilers. Common compatible models include:

ecoTEC Plus 824: (VUW 246/3-5).

ecoTEC Plus 831: (VUW 316/3-5).

ecoTEC Pro 24: (VUW 246/3-3).

ecoTEC Pro 28: (VUW 286/3-3).

Note: While it fits many models, always verify against your boiler’s 7-digit serial number, as some high-output models (like the 837) may require a larger 30 or 36-plate version.

Technical Tip: If your central heating works fine, but your hot water is lukewarm or fluctuates in temperature, the plate heat exchanger is likely "sludged" or scaled up. Similarly, if the boiler overshoots in temperature and cuts out during a hot water demand (Fault F.20 or F.24), it indicates a blockage in this component.

Maintenance and Installation Advice
Replacing the plate heat exchanger requires the boiler to be isolated and the primary circuit to be drained. It is essential to replace the sealing O-rings at the same time to prevent leaks. To protect your new heat exchanger, we highly recommend installing a Magnetic System Filter and treating the system with a high-quality inhibitor to prevent black magnetite (sludge) from clogging the new plates.

Essential Companion Products
To ensure a professional and long-lasting repair, the following genuine Vaillant and maintenance products are recommended:

Direct Product Link: Vaillant DHW Heat Exchanger - 178973

Sealing Kit: Vaillant Gasket C-Type Pk10 - 178969

Pressure Monitoring: Vaillant Water Pressure Sensor - 0020059717

Specialist Support and Local Collection
Is your hot water failing to reach the desired temperature? Our trade counter team can help you diagnose whether the issue is the plate heat exchanger, the diverter valve, or a faulty NTC sensor.

Visit our trade counter and Bathroom Showroom at 61 Fullers Road, E18 2QB for expert technical advice and quick access to genuine Vaillant spares.