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Vaillant ecoTec F75 / F.75 Fault Code - Causes and How to Fix

June 23, 2021

The Vaillant F75 fault code is probably the most common fault code on Vaillant ecoTEC boilers.

It’s quite a vague fault code and can relate to several issues, not all are necessarily boiler faults.

Vaillant’s official explanation of the fault direct from the manual reads:

F75

Fault, no pressure change detection when starting pump

Water pressure sensor and/or pump defective, air in heating installation, too low pressure in boiler; connect external expansion vessel to return

When the boiler receives a demand for heat, from either the Central Heating controls or a hot water demand from a tap the internal pump will be one of the first components to operate. When the pump starts there will be a sudden spike in pressure within the heating system and boiler, it’s this pressure increase the pressure sensor is looking for. If the sensor doesn’t detect the spike in pressure, it will send a message back to the boiler PCB indicating it has detected a fault and it is not safe to continue the ignition sequence.

Vaillant F75 error – pump fault causes

Vaillant’s early ecoTEC boilers circa 2005 were manufactured with a pump produced by a company called Wilo. Wilo is a reputable manufacturer who still makes pumps today, however, this pump was known for its high failure rate, and they were particularly prone to leaking and splitting. Wilo’s reputation suffered a severe knock it hasn't been able to fully recover from

Quickly spotting the error, around 2007 Vaillant ecoTEC boilers were and still are manufactured with a pump from a company called Grundfos, Grundfos is the leading name in domestic heating pumps and the question ‘why wasn’t Grundfos used from the start?’ could be asked.

F75 error – pressure sensor fault causes

The Vaillant Ecotec boiler’s pressure sensor has had three separate upgrades since it was launched in the original Vaillant Ecotec boiler back in 2005. The first sensor, which was Orange, had a very high failure rate. Again, Vaillant quickly recognised the fault and replaced it with a new black sensor which is still in use today.

F75 faults relating to the pressure sensor were often not due to component failure but rather due to poor installation and a lack of adequate and proper maintenance.

Sludge and magnetite deposits which naturally develop in Central Heating systems over time can build up and block the sensor, a system that wasn’t cleaned thoroughly during the boiler installation process or an appliance that has had poor maintenance will develop higher levels of containment in the system and hence be more prone to the Vaillant F75 fault.

The original orange sensor and subsequently the updated black sensor was positioned low down in the boiler near to the pump so they could easily detect the pressure increase when the pump turned on. Vaillant realised however that any loose debris in the boiler and system would be forced into the sensor causing an F75 fault code, with this realisation Vaillant developed the F75 kit.

The Vaillant F75 kit consists of some new pipework and the black sensor, by removing the old sensor and capping off the original aperture Vaillant re-designed the layout of the Ecotec allowing boiler repair engineers to move the sensor away from the pump making nuisance F75 faults less likely.

How to fix the Vaillant F75 fault code

As there are several faults or underlying issues that could cause the Ecotec F75 fault code it is always advisable to have a GasSafe registered boiler repair engineer check your boiler installation whenever a fault code is displaying on your boiler.

A few simple checks you can do to get your boiler firing while you wait for a local repair engineer are to check the boiler pressure and check for air in the heating system.

On the front of your Vaillant Ecotec boiler in the bottom right corner, you should see a pressure gauge. The black needle should be somewhere in the middle of the grey section, about 10 o’clock.

Depending on what model of Vaillant Ecotec boiler you have and its age the filling loop could be internal and operated by two grey ‘keys’ below the boiler which read closed or, somewhere on the system a silver flexible tube that joins two pipes together.

If the pressure is fine, then the fault will probably be located inside the boiler housing and a GasSafe registered boiler repair engineer will be needed.

You should never remove the casing of your boiler to look inside or try to replace any components within the boiler.

Heatsy are Vaillant boiler repair specialists, and we are proud to be recognised as Vaillant Advance installers.

If you are experiencing the F75 fault code with your Vaillant Ecotec boiler, call us for a boiler repair today.

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