anyone help with Baxi 105 HE problem?

Hello new to this site - hope someone can help with this problem.
Baxi 105 HE - ch stopped working, in dhw mode was working ok then after a while boiler would ignite when turned on although there was no demand for water, will only turn off to reduce temp for 30 secs then it reignites, thought the dv s passing, renewed internals, problem still there, when boiler is switched on micro switch is made immediately and ignites. New pcb had been fitted couple months ago, boiler has been serviced, problem has just arisen. When boiler is swwaitched off (no power) there is a noise from the boiler as if water is circulating.