Water Heater Advice Please

Hi All, well we now have 2 trips under our belt in our caravan and most of it has gone well.  We have a carver water heater and on our 2nd trip we noticed a constant drip from the drain plug which we hadn't noticed on our 1st trip.  We sealed it with plumbers tape and it stopped dripping, BUT the water then got far too hot. We are now concerned it should have the drip to alleviate any pressure. Can anybody advice if it should drip or not as Carver have gone bust so helpline available.  Thanks