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What Is a Vaillant Pressure Sensor?

The Vaillant pressure sensor, sometimes called the Vaillant water pressure sensor, monitors the water pressure inside your heating system. It sends pressure readings to the boiler's control board so the boiler can operate safely and efficiently.

If the sensor gives incorrect readings, the boiler may stop working or display a fault code even if the system pressure appears normal.

Vaillant-Water-Pressure-Sensor
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Key Features

  • Monitors heating system water pressure.
  • Sends digital readings to the boiler control board.
  • Helps prevent damage caused by low or high system pressure.
  • Supports safe and efficient boiler operation.

If you suspect a pressure sensor problem, it's worth having the boiler checked before replacing parts unnecessarily.

Where is the Vaillant Pressure Sensor?

The exact location depends on the boiler model.

  • Older Vaillant boilers usually have the sensor towards the lower left-hand side.
  • Many ecoTEC models position it below the heat exchanger on the return pipe.

Access should only be carried out by someone qualified to work on the appliance.

Why the Pressure Sensor Matters

Most Vaillant boilers operate best with system pressure between 1 and 1.5 bar. The pressure sensor continuously checks this level and tells the boiler when pressure falls outside its normal operating range.

Without accurate readings, the boiler may lock out, heat inefficiently or fail to start.

Common Vaillant Pressure Sensor Faults

F73 – Pressure Sensor Fault

F73 usually means the boiler cannot read system pressure correctly. Common causes include:

  • Failed pressure sensor.
  • Loose or damaged wiring.
  • Corrosion or sludge affecting the sensor.

F75 – Pressure Detection Failure

F75 appears when the pump starts but the boiler cannot detect the expected pressure increase. Possible causes include:

  • Blocked or faulty pressure sensor.
  • Pump fault.
  • Low system pressure.
  • Sludge restricting water flow.

What Causes Pressure Sensor Faults?

Pressure sensor faults are not always caused by the sensor itself. Possible causes include:

  • Worn pressure sensor.
  • Damaged wiring.
  • Magnetite or sludge inside the heating system.
  • Low water pressure.
  • Pump, expansion vessel or PCB faults that produce similar symptoms.

A proper diagnosis helps avoid replacing working parts.

Troubleshooting a Vaillant Pressure Sensor

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Before arranging a repair, check a few basic points.

  1. Check the boiler pressure — confirm it's around 1 to 1.5 bar. If it's low, top it up using the filling loop and monitor whether it drops again.
  2. Inspect visible wiring — look for loose or damaged connections where accessible. Do not remove boiler covers.
  3. Reset the boiler — a reset can clear temporary faults. If the code returns, further investigation is needed.
  4. Arrange professional testing — a qualified Gas Safe engineer can test the sensor, wiring and pressure response using the correct equipment. Persistent F73 or F75 faults usually require this level of diagnosis, and the issue may involve the pressure sensor, pump or another component within the heating system.

For an overview of other Vaillant fault codes and what they mean, see our Vaillant boiler fault codes guide.

When Should the Pressure Sensor Be Replaced?

A replacement may be required if:

  • Cleaning the sensor doesn't restore accurate readings.
  • Testing confirms the sensor has failed.
  • F73 or F75 continues after pressure and wiring checks.

Replacing the sensor without diagnosing the underlying cause can leave the original fault unresolved.

Why Choose Serviceteam for Boiler Repairs?

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Our Gas Safe engineers diagnose Vaillant boiler faults every day across London. We provide:

  • Experienced Gas Safe registered engineers.
  • Clear pricing.
  • Guaranteed workmanship.
  • Repairs for pressure sensor faults, pumps, PCB issues and other boiler problems.

If your boiler keeps displaying F73, F75 or pressure-related faults, arrange a professional inspection before the problem leads to a complete breakdown. Our boiler repair in London service can diagnose and repair the problem safely.

Frequently Asked Questions

Can a Vaillant pressure sensor be cleaned?

Sometimes. If sludge is causing inaccurate readings, cleaning may solve the problem. In many cases, replacement is the more reliable long-term option.

Where is the pressure sensor located?

Usually on the return pipe near the heat exchanger, although the exact position varies between models.

How do I know if the pressure sensor has failed?

Typical signs include recurring F73 or F75 faults, pressure readings that don't change correctly and lockouts despite the heating system being correctly pressurised.

Need Help With a Vaillant Pressure Sensor Fault?

If your boiler is showing F73, F75 or other pressure-related errors, our Gas Safe engineers can identify the cause and carry out the necessary repair.

Get in touch to book a boiler repair anywhere in London.

Get lightning fast quotes. Alternatively, we do offer site surveys where needed.