drayton RF wireless / Grant outdoor combi.boiler keeps shuting down ?

what else can I try? have fitted new battries to the FR. re programded the unit as instructions as far as I can see all is working. boiler is upto 1 Bar which is correct for the system. the problem is the boiler some times will not start. then it will and maybe run for 5mins or it could run for 10 to 15 mins and shut down then will not start. then I have to shut erery thing down and start again. thanks for looking at my problem.
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