Vaillant Boiler Flow Sensor Replacement

This vaillant flow sensor detects domestic hot water flow so the boiler knows when a tap is opened and can fire correctly. Over time, debris or limescale can affect readings, which may cause no hot water, hot water cutting out, or temperature fluctuations. Replacing the correct Vaillant flow sensor restores accurate flow detection and helps bring back stable hot water performance.

Compatibility :

• Ecofit Pure: 825, 830, 835
• Sustain: 825, 830, 835, 24, 28, 34
• Home Combi: 25-A, 30-A, 35-A

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 this vaillant flow sensor do?
It detects hot water flow and signals the boiler to start and regulate heating for taps/showers.

2. What are the common symptoms of a faulty flow sensor?
No hot water, hot water cutting out, unstable temperature, or delayed response when you open a tap.

3. Which boilers does this fit?
It fits selected Ecofit Pure, Sustain, and Home Combi models (see compatibility list).

4. How do I confirm the correct part number?
Match your boiler model on the data badge and confirm 0020211945 in the parts list/diagram.

5. Do I need an engineer to fit it?
If you’re unsure, use a qualified heating engineer to avoid leaks and incorrect installation.