Have a cottage and guests have had heating and hot water on constant and then put on the emerssion heater. Now they tell me no hot water at all.. could this have caused the problem and what should I try to do to fix?

No hot water, check your hot water system/tank. Send a qualified plumber/hot water tech. What kind of emersion heater are you talking about. Doesn't it have a separate tank? More detailed information of your systems would surely help.