I have a HONEYWELL immersion heater. Two probs. First, the HW tank seems to be boiling its own water!! We have not had the need to turn on the HW for six months as we still get scalding water from the taps. The HW tank makes a periodic \\\'kettling\\\' noise, esp. after we have used hot water. What\\\'s wrong?? Second, the CH doesn\\\'t work. When the CH is switched on it fires up the boiler which remains on for only about 2mins then switches itself off. Again, what\\\'s wrong??