If the boiler is tripping its most likely a fault sensor, there two circuits in the boiler one for CH the other the HW.
The heat exchange, multi port valve or temp sensor may well be faulty resulting in a short and tripping the boiler.
Since your not presented with an error code, its difficult too identify the fault, however this will require a boiler engineer to attend and strip down the components and test individually.
The fact its not affecting combustion, would suggest to me its a rather inexpensive part such as a sensor rather than a control board or heat exchanger which would have cost 100s.
If you would like me to recommend an engineer in your area, please provide your postcode.