Trouble with having so many members your query soon disappears from sight!!!!
I had a similar problem to yourself and found that on the outside of the water heater, near the top, is a clear plastic tube running from a red non return valve to the outside of the motorhome. The red non return valve was not working and allowed the hot water to slowly drip out to the outside of the van. Even when filling up with cold water there was always a slight seepage. I obtained a new valve from a local caravan shop cost about £7. It is easy to replace.
Ian
I had a similar problem to yourself and found that on the outside of the water heater, near the top, is a clear plastic tube running from a red non return valve to the outside of the motorhome. The red non return valve was not working and allowed the hot water to slowly drip out to the outside of the van. Even when filling up with cold water there was always a slight seepage. I obtained a new valve from a local caravan shop cost about £7. It is easy to replace.
Ian