PLEASE HELP?

Hi,

I require an experienced and competent gas engineer/boiler technician, to repair my boiler please.

Boiler: Potterton Puma 80 (permanent pilot).

Problem: If I run the hot water CONTINOUSLY for more than 15 minutes, or CONTINOUSLY run the central heating for more than 2 hours, the boiler cuts-out (with a click) and the pilot light goes out. If I then re-light it, it's back to square one.

So far, I've had two different engineers attempt to fix the problem, without success.

Between them, they have replaced the following parts in the boiler :-
- Extractor fan assembly,
- Wax capsule,
- Thermocouple,
- auto air vent,
- flowswitch assembly,
- microswitch,
- overheat stat.

Unfortunatelly, replacing ALL of the above still hasn't fixed the problem.....

They have run out of ideas.......

Can YOU help ??? PLEASE ?

Additional info: The boiler pressure remains constant: 1 Bar with the central heating not running and 1.5 Bar with the central heating running.
There are no unusual noises, etc. When the bolier is running it sounds perfect, heating works great and hot water is hot.

I need your help please. Can you fix my boiler ? I can't afford a new boiler at present, so I must get this one fixed for now. Your help will be MUCH appeciated.

Thank You