Hi, you need to reprogram the new PCB with the25C settings. Had the same problem myself, the diverter valve is going to CH when the hot tap is opened causing the chamber to overheat and bang.
The Settings are:
P1-00
P2-06
P3-00
P4-00
P5-07
P6-02
P7-80
P8-04
P9-20
P10-60
P11-00
P12-28
P13-80
P14-85
P15-04
P16-10
P17-20
P18-57
P19-10
P20-15
P21-25
P22-10
P23-80
P24-40
P25-00
(Settings obtained from my old PCB)
Use the power and M button to enter the set up and the radiator dial to adjust.
Hope this helps.
Ryan
December 2010