Vaillant Boiler F73 Fault – Error Code Guide

The F73 error code relates to the water sensor and affects the aquaTEC, ecoTec Plus and ecoMAX models of Vaillant boiler.

This error code signifies that the water sensor is operating incorrectly, which can signal a leak or be due to faulty parts.

The F73 is considered a minor error and is easily and inexpensively resolved, but because it concerns the boiler’s internal parts an engineer should be called to deal with the problem.

What Does A Vaillant F73 Error Mean?

The F73 error code is caused by a low-pressure water sensor fault (as is the F74 code on older models – the F73 is the updated error code for this fault).

The various sensors within a boiler detect whether it is working correctly, monitoring air pressure, gas flow and in this case water pressure. When the pressure is incorrect, the boiler will lockout and an error code will be displayed.

The F73 code means that the water pressure sensor is faulty.

What Causes A Vaillant F73 Error?

The F73 is shown when the water sensor detects inadequate water pressure, which is usually caused by a leak somewhere in the system; however, when the sensor is faulty it gives these readings incorrectly.

A sensor can give intermittent or incorrect readings for several reasons. It could be due to a loose or damaged (water- or otherwise) connection with the PCB, or the sensor itself could be faulty.

Loose Connections

Boilers are full of vibrating parts, such as the pump and fan. Over time this can cause wiring connections to become loose and work less effectively.

Water Damaged Wiring

The most common cause of faulty wiring, which can cause incorrect readings, is water damage resulting from an internal boiler leak. These leaks usually originate from broken heat exchangers or pumps with damaged seals.

The condensation resulting from these leaks settles on electrical parts and wiring and causes them to malfunction.

A Faulty Sensor

It may be the case that the sensor itself is faulty. This could result in the PCB receiving occasional incorrect signals, or if the water sensor has a permanent fault then the boiler will repeatedly shut off.

How To Fix A Vaillant F73 Error

If the F73 error code is showing because of a leak in the boiler or elsewhere in the system then this will need to be fixed to resolve the issue, which an engineer can do for you.

An internal boiler leak can cause water-damaged wiring, and an engineer will first determine the origin of the leak and then examine the rest of the boiler’s parts for water damage.

A leak within the boiler could be caused by high pressure or limescale build-up, which an engineer can resolve by bleeding the boiler or flushing the system.

If the water damage is severe and many parts need repairing or replacing, then you may want to consider investing in a new boiler.

If the fault code is displaying due to an intermittent fault in the water sensor, then resetting the boiler can fix the problem.

However, if this is a common occurrence or if resetting the boiler has no effect, then the sensor could have a permanent fault which a gas safe engineer will be able to diagnose.

The engineer will examine the wiring and test the water pressure sensor, and repair the wiring or replace the sensor if necessary.

Can You Fix A Vaillant F73 Error Yourself?

When this error code shows, you may be able to tell whether this is down to a boiler leak if you spot drips of water or a puddle underneath your boiler, or you might have heard gurgling noises coming from inside the boiler.

This is helpful information to give you Gas Safe Engineer before they come out so they are prepared for what they will need to deal with, but you should not attempt to work on the boiler yourself as it is unsafe to do so and could potentially result in further expensive problems.

A leak in the boiler can sometimes be caused b high pressure in the system, so you could try bleeding the radiators and towel rails in your property – however, this is usually down to high pressure within the boiler itself and boilers should only be bled by a Gas Safe Engineer as it involves removing the casing.

Does An F73 Error Mean My Boiler Is Broken?

No – an F73/74 is considered a minor fault. As long as this is the only fault code displayed (as opposed to multiple codes showing at once) then the fix should be easy and inexpensive.

Is It Safe To Use The Boiler With An F73 Error Code Showing?

You shouldn’t. Since this error is caused by a leak, the lockout protects the internal boiler parts and also prevents damage to your property – when there is a leak somewhere in the system this causes water damage to the surrounding area, and the boiler running will release more water into the leaking system.

This risks further damage to your property and possibly expensive repairs, so you should not use attempt to use the boiler when this error code is showing.

Do I Need To Reset My Vaillant Boiler After An F73?

If the error code is being shown due to a faulty water sensor, then this should only happen occasionally and resetting the boiler should resolve the issue. However, if this is a recurring problem you should call an engineer to resolve the issue and potentially replace the water sensor.

How Much Does A Water Pressure Sensor Replacement Cost?

The parts alone are inexpensive, costing £50 or less. However this kind of error is tricky to diagnose and you will end up paying for up to 2 hours of labour, plus more if the part needs replacing.

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