Vaillant Boiler fault?? Egg timer, water flow in air gap

[bobmoo79]

I was outside earlier and noticed water running from on overflow pipe so went to check the airing cupboard.
I have water flowing across the air gap. Not dripping, flowing.
I also occasionally have a flashing egg timer symbol on the Vaillant boiler display (ecoFIT pure).
Both hot water and heating are working.
Boiler pressure seems ok according to the display on the boiler and the needle gauge in the cupboard (about 1.5bar)

Any idea what this is and what i should do?

 

[CountryFan]

Egg timer is anti-cycling mode. The flowing water is either a failed expansion vessel, safety relief valve not seated correctly or both. You may need a G3 registered engineer to work on that unvented cylinder.

 

[terryplumb]

Call out an engineer. If you want to save water,close your mains cold water stopcock. Put it on ,as and when you need water.