I have just replaced the flowswitch on my heatslave 15/19 with the newer horizontal mounted type, the old one was the vertical mounted type slight modification of pipework required for those that are familiar with the older heatslaves. Problem is that when the cold tap on the sink is switched on you here the relay activating and burner lighting as if dhw is demanded.I assume this is because there is a mains pressure drop. What can I do about this? And before anyone asks the switch is the right way round and the arrow follows the direction of flow.