valient turbomax 242eh central heating will not operate once it reaches tem?

242 eh installed with 3 rads the boiler works fine in hot water when in ch and hot water mode ch reaches temp then shuts off and will not relight. pump dissapates heat then stops. to relight fused spur needs to be switched off then on again but boiler will only operate when rads have cooled. pressure appears high 2.5 bar .the boiler does not lock out via black reset button pressing this will not ignite it only via fused spur. if water turned on it lights and works normally even after lock out of ch. one radiator feels hotter than return pipes from boiler the other radiators same temp as return pipe also a leak develops on this hotter radiator when temp reached this rad is mad hot.