vokera combi excell 80 sp . trying to ignite the pilot light .hold button in .press ignition ,flame comes on .hold button in for 30 secs ,release slowly.every time at the final point of release light goes out .
Could also be a dirty pilot,
does the flame touch the thermocouple ?
is the flame strong and blue ?
Worst case - new gas valve required.
Get a Heating Engineer to sort it out.
I wouldn't advise it - but - If you do attempt changing the thermocouple yourself then make sure you put the boiler case/combustion chamber front back on correctly - essential for the safe operation of room sealed appliances.
Do not attempt changing the gas valve yourself. Pressures need to be checked/set and a gas tightness test carried out.