Hot and cold water from a Vokera Excell SP80?

Yes, a dirty Venturi, even a small build up of deposit stops it working. Got to be clean as a whistle to work properly. Hot -cold -hot domestic hot water cycling is almost always this on this and similar aged Vokera models.
You need to take the venturi out of the boiler to clean it up properly, gently using a small needle file . A job for the corgi man, as its in the sealed chamber. Shouldn't recommend anyone tries it on a public bulletin board. But if you must, make sure you download and read the manual pdf from Vokera. You could even do the classic boiler service - hoover the dead wasps out of the bottom of the combustion chamber, while you are at it.....

c++
December 2010

Thank you Brian and Ricky. I'll follow your advice and pray it works Ok. Thanks again.

David
December 2010

i would suggest that the likely cause is a blocked venturi or faulty air pressure switch (aps) to check simply remove the front combustion plate if when you run the hot water tap the appliance stays lit then i would check the venturis to check connect a water u gauge or digital manometer to the top nipple which is just above the fan there is a clear tube connected to it at present which goes to the aps remove this tube and put on the tube from your manometer run the boiler you should get at least 3mb if you dont clean the venturi and retry

ricky
December 2010

make sure you're not turning the taps on too far the flow rate through the boiler is critical in winter if that's ok then you're looking at a faulty h/ water stat or blocked heat exchanger

brian
December 2010