Sounds like you have had someone without any diagnostic skills who just replaces parts.
Why has it not cost you much?
Pressure loss is caused by a leak. In or outside the boiler.
Without doing tests its difficult to suggest why the CH only runs for 30 min.
When it stops what are the diagnostic lights showing?
There is a common cause for that but it would also affect the DHW as well. Can you use DHW for 30 min without boiler stopping?
Tony
Why has it not cost you much?
Pressure loss is caused by a leak. In or outside the boiler.
Without doing tests its difficult to suggest why the CH only runs for 30 min.
When it stops what are the diagnostic lights showing?
There is a common cause for that but it would also affect the DHW as well. Can you use DHW for 30 min without boiler stopping?
Tony
If you ask for help on a forum then it is sensible to provide any further answers when someone tries to help you!