Vaillant eco tec plus 831 pressure issue

4 Oct 2022
Reaction score
United Kingdom
Hi, I've got a Vaillant eco tec plus 831 and it had the error code F75 Fault: Pump/water shortage. I'd noticed earlier that the pressure bar looked low but not thought much of it until the heating didn't come on and I saw the error code. I thought I knew what to do and turned the 2 taps underneath to let more water in for about 10-15 seconds. Then the system refired and the heating came on. However, I think I may have overdone it as it's flashing 3.7 and I suspect that may be too high. I've tried running a hot tap but that doesn't seem to make a difference. Any tips would be very gratefully received! Thank you :)
Sponsored Links
F75 is often a blocked sensor, sometimes a failed pump. Yes 3.7 is far too high and it won’t work. You need to drain the water out, although I suspect the pressure relief valve has operated as they’re designed to open at 3 bar and above.
Hi Chris,

Thank you so much. I guess the pressure is my fault... it did work in terms of kick starting it to work again. It's now down to 3.3 (I did run the bath in case that helped) and the heating will be going off soon... I'm not sure how to drain some water out though?

Thank you so much again,
That's weird, I hope good weird, it's stopped flashing the pressure and now just says 47 degrees C. the bar on the right does show the level as at the top line so I presume just inside acceptable I'm thinking maybe I've got away with it... the heating has just gone off so maybe that helps too? Do you think I need to do anything or just keep an eye on it? I do need to book a service anyway.

Thank you again,
Sponsored Links
Needs a proper service and the expansion replenishing. Get a local recommended gas man in!
  • Like
Reactions: CBW
Thank you very much, I will get back to my usual gas company.

Thank you again to everyone for your advice :)

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local