“If you think it’s expensive to hire a professional to do the job, wait until you hire an amateur” Red Adair

Mark Ray;

Ex-Vaillant Service Engineer

Repairs & Breakdowns

Annual Servicing


Landlord & Tenants

Call 07515-687740  9am-4.30pm

Mon -Fri 8am-9pm (Sat 9am - 1pm)

Need support?

I’ll answer your questions FREE of charge at;


or CALL ME DIRECT ON - 07515-687740 before 8pm

East London

South London

North Kent


This site has been updated to a platform that supports mobile devices.


Thank you.



The ecoTEC suffers with an F.75 fault code, which can frequently occur, and has no defined remedy. There are a number causes, that throws up this code, which makes it virtually impossible to diagnose immediately.

Frustrating, and expensive, it’s all a bit disappointing. However, some of the causes are listed below, to help you understand how difficult it is to cure, and why your engineer may be struggling to deal with it. Irrespective of what company or individual engineer you may employ.

Ok, so here we go,

First, the pressure sensor has to read a pressure increase of 0.2bar when the pump activates. With the appalling pressure gauge design, it’s impossible to determine what pressure you have to begin with.

So, if you’re quick fingered enough, you can use the ‘-’ (minus) button to show the digital pressure reading on the display. But! it only comes up for a few seconds, so you need to have the pressure displayed when the pump kicks in, again.. not brilliant, and you have to be bloody quick, or well practiced.

Basically, this tells you nothing, other than the sensor isn’t picking up a pressure rise when the pump kicks in.

Below are some things that need to be checked, and shouldn’t cost anything to check out.

But here’s some good news.... I think?

You can install a retrofit modification, so if you end up sitting on London Bridge contemplating suicide, having failed at every hurdle, Vaillant will graciously supply you with a kit for a cost of well in excess of £100.00.

Faulty pressure sensor:

Now modified part available.

Remove and clean thoroughly.

Should be ‘black’ not ‘orange’..


Now modified part available


Just check it’s actually running freely, with and without power.

Expansion Vessel:

Don’t know why, but these vessels are always empty, every time I see one?

With no charge, especially on larger systems, can throw up all sorts of problems, including F.75

Main Heat Exchanger:

Real problems with blocking up. The heating system needs to be absolutely pristine.

Best advice, fit a filter on the return, as soon as possible.

Remove and wash out the best you can, if there’s any evidence of crap in the boiler/system

Built-in filter:

In the hydroblock, there’s a white plastic filter, intended to protect the plate.

To be honest, it’s easier to remove the plate and flush it out, than remove the filter.

So a bit of a waste of time really..

Access is via the sensor housing, and you’ll need to remove the flow connection from the main heat exchanger.

Deep joy! but can be done easily once you’ve done a few.

Good luck..


It is a criminal offence to work on a gas appliance if you are not qualified, and licensed to do so.

ALWAYS consult the manufacturers user instructions for guidance. The instructions above are for guidance only. If unsure of any procedures, call a boiler specialist, who holds the relevant qualifications, and GAS Safe Registration.

F75 Fault Code:

Home    |    Blocked Heat Exchangers    |    Hot Water Problems    |    F.75 Fault Code    |    My Charges    |    Technical Help Area    |    Installations   |   Where & When