Richboiler used his keyboard to write :
Hi - I've had a gas fitter out twice now to repair it but its still not
sorted. The boiler fires up ok but after 30mins turns itself off. The central
heating pump has been replaced and the gas valve. After the fitting of the
new
gas valve it ran ok for 5 days but then has gone back to square one. Any
ideas?... I've been in touch with Potterton/Baxi to see if II could get an
engineer to come out but they don't support this model any more - the boiler
is 14 years old and I'd like to repair it rather than replace it.

Does it produce any fault codes?

Does it reset itself after the 30 minutes, or what do you have to do to
get another 30 minutes run out of it?

What model is it?

Might it be the overheat stat operating?