Biasi prisma boiler fault

[Mog10]

Hi there, wondered if anyone can help, I have a biasi prisma boiler, 24S combi I think, the problem being when the heating or hot water is turned on the flame stays lit for approx 10 seconds then goes out, then lights again, then out etc etc.

This is extremely irritating when trying to shower as it changes from extremely hot to icy cold every few seconds.


Any ideas would be much appreciated.

Thanks in advance

 

[weargas]

Could be an airflow problem on the prisma. Easy way to test is to remove the combustion case cover and run the dhw. If the flame stays on it's definately airflow. Either a blocked venturi or faulty air pressure switch most likely.
Removing the combustion case cover is really a RGI's area mind! The boiler cannot be run without this cover it's purely a testing procedure