Vokera Unica he boiler blowing water out - PLEASE HELP US

[paulwilson]

Hi I was hoping someone could help regarding my boiler, I have trawled the internet with no success.
We have a Vokera boiler which we have had for 3 or 4 years without too many problems, the fan went last year and we have had a few pressure problems which I think were due to rad leaks.

The problem is I fill the boiler up to 1.5 bar pressure making sure all rads are bled and the pressure still at 1.5, I turn the boiler on and it runs for approximately 5 hours before it shuts off, you can then hear clicking as though its starting to fire up but obviously there is no water.
When I went outside yesterday I noticed a damp area where the blow off is, can anyone help as to what it may be? I am going to call an engineer out today or was thinking off going on one of the British Gas insurance schemes whatever is cheapest. Thanks to anyone that can help kind regards Paul

 

[MANDATE]

most likely lost some air from the expansion vessel.
The vessel should have full capacity of air so that when heating on and volume of water expands, the extra water has somewhere to go.
The air gets compressed and its pressures rises.
This should normally be about 1bar rise, so your 1.5bar will go to 2.5bar.
With reduced air capacity, the smaller amount of air gets compressed to a much higher pressure and this activates the Pressure relief valve (at 3bar)

Problem is that PRVs don't always seal properly after being open due to sediment between washer and seating face. Normal practice is to fit new PRV but only after the expansion vessel problem has been fixed.
When you put heating on, try watching the pressure gauge and see what pressure it rises to.
You could also try starting with a little lower pressure ie 1bar

 

[paulwilson]

Ok thanks very much, reading what you have put sounds very familiar with whats been going on and I have spoken to a plumber who is calling over tomorrow, he spoke about recharging the vessel to see if that could fix the problem and if that failed he would fit a new one and a new relief valve.

I do remember watching then dial and watching at go really high like 3 bar maybe slightly over before being shot out into the garden