This boiler dose not fire up when there is a demand for DHW, but the it fires up when there is a demand for CH. The diverter valve works ok its head extends when there is a demand for DHW and engages with the microswitch on top of it. Also the pump is working but the boiler does not fire. I also tried to the run CH and open the hot tap and as soon as I do that the boiler stop firing. Any idea please