Hi my british gas 537/1 boiler heats the water OK but won't heat radiators and the display reads 59 then drops to 39 works for a few seconds until it goes back up to around 60 then shuts out again

Hot water and central heating are two different systems.
Hot water systems in the UK are limited to 60 because higher than that would scald. If it ever goes above 60 you have a problem.