First off, I've had problems with the hose to the water heater popping off ever since I got my boat new. It always happens around an hour or so after turning on the water heater, eg., just after getting to the boat. Worked with the dealers service dept. and the best theory we could come up with was some air in the heater that expanded as it got VERY hot; resulting pressure blows the hose off. I then hear the pump running and know it's time for another dive into the water system.

I have tanks go dry all the time as I only use one at a time, so they get emptied and 'refreshed'. I also like to have some indication of water use so when a tank goes empty I know I have one (or 2) left and can manage water appropriately. When a tank goes dry, I open the valve to the next tank and close the valve to the dry tank. Takes a few minutes to draw water, but has never been a problem 're-priming', as long as you leave the sink valve open. If you don't it'll never prime as the pressure to the sink won't let the air pass out of the system.

Possible that running dry for a long period could damage the diaphram in the pump too, I don't let mine run dry for long.

Hope that helps .!

The hot water takes maybe 15 to 20 minutes to heat up. Please, turn it off when it's warmed up. When you run out of hot water, turn it back on for another 15 minutes. The system does not need a prime, because the pump is able to pull the water through the system.

Akorinek,

Are you sure you that did not just run the tank dry, I agree with Stu the pump should be self priming unless it is sucking air either from an empty tank or a air leak in the supply hose.

As for the water heater, I do often leave mine on while at the dock when I am aboard the water heater does have a thermal switch and will cycle on and off. If I am not aboard I trip the circuit breaker turn off the water heater. I sometimes wish the thermal switch was adjustable as the water gets scalding hot, though with a small tank the high temp makes up for the lack of volume as you dilute the hot water with cold and wind up with a longer supply of hot water.

[QUOTE=Steve Frost;3446]...the water gets scalding hot, though with a small tank the high temp makes up for the lack of volume as you dilute the hot water with cold and wind up with a longer supply of hot water.[/QUOTE]

Steve, I wholeheartedly agree. I've kept a 180F thermostat on our M25 for the very same reason. The hotter temperature water in the tank from motoring lasts longer doing dishes. ;)

I find that when motoring or motor sailing the hot water out of the tap is hot enough to be used in a French press for making coffee. Now if I tie the cold water side to a keg I could have all vital liquids right at the sink.

Stu, you also would not want to run a lower temp thermostat in your engine as it runs more efficiently at the higher temp.

[QUOTE=akorinek;3443]Here's a quick "what not to do story" followed by a question. I went down to the boat last weekend. My intent was to stay there for a couple days so I kicked on the heat, pressure water, and water heater. Once everything was up an running I decided to step out for a bite to eat. I returned to a hissing noise coming from the water heater. A quick inspection revealed a hose clamp had worked itself loose resulting in a loss of pressure. While the pump was running continuously, I had lost the prime in the system.

First, the obvious lesson: Don't leave your boat unattended with systems running.

Now the question: How to I bleed the air and restore the prime to the system? It appears the pump is positioned above the waterline in the tank because when I disconnected the hose I didn't get any free flowing water. Against my better judgement, and with a look of disgust from my wife I tried to manually suck the water out which was not only rediculous, it didn't work.[/QUOTE]
I too had problems getting the water to flow after the tanks were run dry. I found the strainer that is installed in the water line between the water tanks and the pump was attached to the underside of the salon seat above the pump. This location creates an air lock in the water line and the pump is not strong enough to pull water from the tank unless the water tank is almost full. I relocated the stainer lower in the boat and closer to the water pump. Since then I have had no problems.