My Valliant eco Tec 831 failed today, giving reading of F75, does anyone know what it means. I switched of at mains and boosted water pressure as i have to on this model at least once a month, just one of the faults with this model otherwise ok.

Ian Kirby, December 2009

My boiler would show F75 fault code about once a month after it was 2 years old & out of warranty. I was told to replace the CH pressure sensor as they have a tendency to suffer from ionization (I think I've spelt it right). Vaillant part No 253595. I was also told the new valve is a mod (old valve brown/orange. New valve black and a bit bigger.
I have fitted new valve, flushed & refilled system, no problems since - 13 months ago.
Just recently I have fitted a magnetic filter in the system to be on the safe side.

havago, August 2010

F75 resulted in a replacement pump for my EcoTec 831 which is just on a year old. (luckily these boilers have a 2 year guarantee!)

Mr Boiler, January 2010

THIS BOILER IS A DISATER. IT HAS A DEFECTIVE WATER PRESSURE SENSOR AND THIS MISTAKES THE PUMP AS NOT WORKING. IT MAY OR MAY NOT BE LOOSING PRESSURE AS THE PRESSURE BEING DISPLAYED WONT BE ACCURATE COS THE PRESSURE SENSOR IS NOT WORKING. ITS A KNOWN FAULT AND VAILLANT HIDE IT. TOTAL RUBBISH. ITSD THIS FAULT THAT CAUSES F75, ALIONG ALSO WITH DEFECTIVE PUMPS ( ANOTHER KNOWN FAULT) AND DEFECTIVE AAV (AUTO AIR VENT).

F75 SUPPORT GROUP, January 2010

probable pump failure or pressure sensor. Topping up monthly indicates a leak on the central heating circuit - not a boiler fault.

Constant refilling could lead to a sludging up of the system and hence a pump failure.

Add some inhibitor and have the rad valves and pipes checked for leaks.

neil Di Luca, January 2010