The most typical fault code that appears to show on the Vaillant Eco Tec boiler is F 75.So what’s F 75, and why has this occurred?F 75 is a boiler security mode and locks the boiler out in order to not trigger any inner harm to the boiler.This fault code shouldn’t be usually as a result of boiler being at fault, it is usually all the way down to an exterior downside.If you learn by means of the Vaillant paperwork, it offers you causes on why the fault code has displayed on the boiler display.It states the water strain sensor and or the pump are defective, or attainable air throughout the system.With all Vaillant Eco Tec fault codes, the explanations given are only a information on what to search for, it doesn’t suggest that these components at fault and should be changed.The most typical cause for the F 75 fault code is the system strain has dropped under 0.eight bar. For the boiler to work it must have a minimal strain of 0.eight bar. The traditional working strain when the system is chilly must be round 1.2 bar.The Vaillant Eco Tec has a built-in water strain change which senses the system strain. When the boiler begins up, the inner pump spins and will increase the strain round 0.2 bar, the water strain change senses this and sends a sign to the PCB to start out the ignition sequence.If the sensor doesn’t sense sufficient strain the boiler will show F 75 and go to lock out.To beat this downside verify the strain gauge on the boiler, which is situated on the underside proper hand facet.Be certain that the needle is above the crimson zero and is simply into the gray space.One other option to verify the strain is go to the boiler show and press any of the highest 4 buttons, you’ll discover the show gentle comes on, now press the highest proper hand button on the panel, it’s best to now see a radiator signal, press the identical button once more and it’ll show the bar signal, press once more and it’ll present you the system strain in digital.Among the new Vaillant boilers now solely include the sort of strain show so this would be the solely option to verify the strain.Ought to the boiler strain be right then we now have to verify the water strain sensor itself? If the system has a construct up of inner sludge, the sensor can get blocked and isn’t in a position to sense any strain, so the boiler won’t hearth.Vaillant moved the place of this sensor, it used situated on the backside of the boiler, now it’s fitted immediately under the warmth exchanger connections on the left hand facet.The explanation they moved it was when it was situated on the backside, when the boiler was off the sludge might enter the sensor and trigger it to dam, by shifting it to simply under the warmth exchanger it stops the sludge.If you happen to discover you can’t reset your Vaillant Eco Tec then the perfect advise I may give is to contact an area Vaillant specialist, yow will discover them on the Vaillant web site.Vaillant boilers for my part are of excellent high quality and construct, however like all boiler they should be taken care of, in any other case they’ll finally cease working.