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Vaillant Eco Tec F75 Fault Code Explained


The Vaillant eco tec is a good quality boiler, I have been installing and fixing them for around 10 years since they came on the market.  would recommend them and installed one in my own home. Having siad that nothing is perfect and while I would include this sensor (the f75 water differential sensor) in the design as it prevents the boiler firing when the pump is failed, and therefore over heating. Not every boiler has the fail safe, other high-end boilers do not and it's worth having. The down side is it the fault can occur when there is not actually anything wrong with your pump. Details below;



The Vaillant ecotec fault code f75 can occur on all combination and system boilers in the ecotec range.

It can be quite a persistent and difficult to diagnose the problem as there are a number of parts involved that could lead to the fault code occurring.



Vaillant Eco tec fault code f75 as defined by Vaillant;

“F.75 No pressure rise was detected on turning on the pump Water pressure sensor or/and pump defective Air in the heating system, quick bleeder defective Too little water in appliance; check adjustable by-pass; connect external expansion vessel to return “

F75’s fault codes occur when a particular sensor fails to sense a change in pressure when the pump is expected to come on. This is a very common problem in Vaillant eco tec and these causes are common;


1) Failed sensor.

2) Failed Pump, or failed pump bearings

3) No power from PCB to pump so new PCB or harness required.

4) Faulty PCB not controlling pump or not recognising sensor 

5). Sludged system causing a lack of change is pressure when pump come on.

6). Design flaw in earlier Ecotec’s (require a kit to be fitted so the sensor is relocated).

7) Pressure low in the system so differential in pressure between pump[ on and pump off not occurring.

8) Blocked sensor, sensor blocked with sludge or other dirt so pressure differential not recorded. 7) Air in system, air i the system so pressure sensor, not in direct contact with water so pressure differential sensed. 


Boilers affected include;

Combination boilers; Vaillant Ecotec Pro 24 (combination, Vaillant Ecotec Pro 28, Vaillant Ecotec Plus 824, Vaillant Ecotec Plus 828, Vaillant Ecotec Plus 830, Vaillant Ecotec Plus 831, Vaillant Ecotec Plus 837, Vaillant Ecotec Plus 937.

System boilers; Vaillant Ecotec Plus 612, Vaillant Ecotec Plus 615, Vaillant Ecotec Plus 624, Vaillant Ecotec Plus 630, Vaillant Ecotec Plus 637.

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