sangamo 410 CH controller replacement

Hi, can someone please help me. I have a simple CH system which allows you HW on its own (gravity) or CH&HW together (pumped). This has been run using a Sangamo 410 F4 controller. I presume the system is designed so that if you only call for HW then the boiler gets sent a signal and it heats the tank through gravity (there does not appear to be a cylinder stat). If you call for CH&HW then I presume it sends a signal to the boiler and one through the room stat to the pump. Is there a simple replacement controller? Sangamo recommended a 31033 but when I fitted it, the boiler got no signal when it was switched to CH only the boiler obviously got no signal. From what I can see this controller is not correct. Thanks