Vaillant Ecomax 618 - first not enough, and now too much pressure?

suiko · 22 Oct 2017

hi all

Just turned on the heating for first time in a few months, and I got the F25 fault code, which is "Water switch/System pressure too low".

Pressure was at zero, pretty much.

I found another thread on here and tried adjusting the two valves on the filling loop. When I switched the black plastic one, pressure immediately rose to about 3.0 (i.e. the red zone). The heating came on.

But now I think the pressure is too high? I think it's supposed to be about 1.3. Can I do anything to reduce the pressure?

And what position should the two valves be in for normal operation? At the moment the big black plastic one and the small metal one that needs a screwdriver to shift it.

I'm a bit worried about the pressure thing, so I've turned the boiler off for now.

Jadele · 22 Oct 2017

Bleed a rad till the pressure drops to about 1 bar

suiko · 22 Oct 2017

Thanks. I tried bleeding them all, but it hasn't made any difference to the pressure.

Jadele · 22 Oct 2017

you have to bleed it until the pressure drops not just till water
comes out

Hugh Jaleak · 22 Oct 2017

Both filling valves should be closed unless you need to add water to the system, i.e. to increase the pressure. For the system to increase pressure that quickly may indicate a fault, which may well require and engineer to look at it.

If you can bleed a rad or open a drain valve to lower the pressure to about 1.5, do so, and switch the system back on. See how it behaves, if the pressure goes into the red, then the system shuts down and looses all pressure again once cooled down, then there could be an issue with the expansion vessel.

suiko · 22 Oct 2017

Thanks again. The heating is still on, but I've drained off a fair amount of water (maybe half a litre?), and now it's about 1.5. Anything else? It's due to go off in about half an hour.

Jadele · 22 Oct 2017

when it goes off the pressure should stay the same or thereabouts. if it drops a lot then as above the expansion vessel is shot or needs recharging. replace or recharge are pretty simple procedures.

suiko · 22 Oct 2017

Thanks. Any reason why I got the F25 fault code in the first place? The heating hasn't been on for a few months, but the hot water has been on a couple of times a week. Had the boiler serviced about a year ago, and all ok (12 yrs old but low use).

Now I remember, I think I had this issue once when the boiler was very new. Someone came round and charged me £70 for turning that black valve a touch

Thanks a lot for saving me another 70

Jadele · 22 Oct 2017

boiler servicing should imo be renamed to boiler inspection and test at best. you get that f code because there has been a drop in pressure. it could be anything but could even be where you have banged pipe with the vac cleaner and its really slowly weeping.

suiko · 22 Oct 2017

Yeah, I agree about the "inspection and test"!

Hugh Jaleak · 22 Oct 2017

Possibly a tiny leak somewhere, but if pressure only needs topping up now and again then I wouldn't worry too much, unless an obvious damp patch manifests itself. If it needs topping up weekly, (or more often) then its time to start looking at possible reasons why.

Pressure will drop once the system gets cold, needs to be between 1 -1.5 cold, which will rise slightly when system is at working temperature. Only when it goes off the scale into the red, or the pressure relief is observed discharging boiling water and/or steam does it need looking at.

suiko · 22 Oct 2017

Thanks again. It's been off for over an hour now, and it's dropped to just over 1.0. Will see what it's like tomorrow when I put it on again.

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Vaillant Ecomax 618 - first not enough, and now too much pressure?

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