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When your Vaillant boilers show the F73 fault code, it’s alerting you to a pressure sensor issue. This fault often occurs in popular models like the Vaillant ecoTEC Plus and Vaillant ecoFIT Pure, which are known for their energy efficiency and are part of the wider range of Vaillant boilers. The F73 fault can affect a range of Vaillant boilers and means that the boiler is failing to detect system pressure correctly. At 0800 Homefix, we specialise in diagnosing and resolving Vaillant boiler error codes including the F73 fault to restore your heating system quickly and safely.
What Does F73 Mean on a Vaillant Boiler?
The F73 code on a Vaillant boiler indicates a fault with the pressure sensor. This might be due to:
A defective water pressure sensor
Loose, short-circuited or damaged wiring to the sensor
A faulty connection to the boiler’s PCB (Printed Circuit Board), which can cause a communication fault.
Water pressure sensor signal outside the permitted range or wrong range
This boiler fault results in an inaccurate pressure reading, even when the pressure gauge shows normal. It differs from low-pressure faults like F22 and typically involves electrical or sensor communication issues (sometimes referred to as a communication fault).
Signs of a Vaillant F73 Fault
Boiler display shows F.73 or F73 fault code
Heating or hot water not working
Pressure gauge reads normal, but boiler thinks pressure is zero
Warning triangle or safety switch off icon appears
Possible ignition failure or unstable flame signal fault
Common Causes of the Vaillant F73 Error
Faulty pressure sensor or water pressure sensor defective
Damaged cable harness or loose connector to the boiler’s PCB
Fluctuating internal pressure or incorrect internal pressure measuring point
Condensate pump defective or flue non return flap issue
Incorrect gas family entered or gas group resistor problem
Faulty flow sensor, temperature sensor, or return temperature sensor
Electronics defective, coding resistor issues, or invalid device number
Invalid device specific number assigned to the PCB.
Primary heat exchanger defective or damaged.
Faulty flow temperature sensor or return temperature sensors.
Incorrectly fitted or faulty temperature sensors.
General faulty sensor, such as those monitoring pressure or temperature.
Safety relevant sensor failure, which can trigger a safety switch off.
Issues with the DHW outlet sensor or its connection.
Pressure change detection failure during pump operation.
Insufficient quantity or either an insufficient quantity of water in the system.
Electrical issues involving two power supplies on the eBUS line.
Wrong gas family or wrong gas restrictor fitted, or entered gas family does not match the coding resistor.
Gas family check required due to combustion quality issues.
Sensor signal outside the wrong range.
How to Fix the Vaillant F73 Error
If you’re seeing this Vaillant boiler fault:
Reset the boiler once using the reset button
Confirm system pressure is between 1.0–1.5 bar on the pressure gauge
Listen for signs of gas valve or gas supply pressure inconsistency
If pressure is fine, it’s likely a faulty pressure sensor or pressure sensor issue. In some cases, you may also experience ignition failure or ignition unsuccessful attempts.
We advise not tampering with electronics or internal components. Instead, contact a Gas Safe registered engineer (also known as a Gas Safe engineer) like those at 0800 Homefix for proper diagnostics and replacement.
Troubleshooting & Maintenance Tips
Book an annual servicing for Vaillant boiler repairs and checks
Flush radiators to avoid blockages or inverted flow problems
Check for permanent temperature difference in flow and return pipes
Watch for errors related to the primary heat exchanger or gas valve defective alerts
Replace any safety fuse or inspect for short circuit risks in wiring
Monitor flue gas temperature to prevent safety switch-off faults and ensure proper emissions control.
Preventing the F73 Error in the Future
Maintain consistent water pressure in the system
Ensure regular cleaning of the flue gas path
Avoid temperature change registered faults through correct boiler maintenance
Check and document the gas flow pressure and match it to the correct gas family
Keep a log of basic troubleshooting steps and any previous fault codes
Trust 0800 Homefix for Reliable Boiler Repairs
Our engineers:
Are Gas Safe certified with extensive experience on Vaillant F73 pressure fault
Carry genuine Vaillant ecoTEC boiler replacement parts
Understand all boiler error codes, sensor types, and system-specific signals
Conduct thorough tests including the mass flow sensor, flame detection, and power supplies
We handle everything from internal pressure inconsistencies to incorrect wiring or sensor configuration ensuring safe and lasting repairs.
FAQs
What does F73 on my Vaillant boiler mean?
It means the boiler can’t detect internal water pressure correctly due to a defective or misconnected pressure sensor.
Is this fault dangerous?
No immediate danger, but your boiler’s performance and safety functions may be compromised until repaired.
Can I fix the F73 fault myself?
You can reset the boiler and check the pressure gauge, but internal sensor work should only be done by a professional.
Does the F73 fault mean I need a new boiler?
Not at all. Most cases are resolved with a new pressure sensor or minor wiring repair.
If you’re facing the Vaillant F73 error, don’t delay. Call 0800 Homefix now for reliable diagnosis, Vaillant boiler repairs, and trusted service from Gas Safe engineers.
Book your same-day repair and keep your heating running smoothly.
More info on Valliant Boiler Error codes from the manufacturer here.