Need water heater education please

[julied]

I'm having trouble with heating my domestic water off the engine. It used to heat up the water after about 45 minutes of running the engine at idle. Today it took 3 hours while underway. I only have a basic understanding of how the system works and am hoping that somebody way more mechanical than I can enlighten me!

Here is what I have:
Westerbeke 70 engine with a Flowcontroller mounted on the end of two pass exhaust manifold (text taken from Westerbeke 70 owners manual). I have a water tank that appears to hold about 25 gallons of water. There is a pressurized remote expansion tank located above the water tank (both the water tank and expansion tank are mounted higher than the engine).

What should I check for for possible problems causing such slow water heating?

ANY information on how these systems work would help lead me an answer. (And a hot shower!!)

~Julie
Kia Ora in Seattle

[artbyjody]

It could be the heat exchanger is clogged with calcium or other deposits. That would be where I would start - with flushing the system. In Seattle as well so you can PM me if you need a hand doing so...Go to the song chain and put up four more posts..

[julied]

Thanks! I talked with a friend who was a mechanic earlier in life and he had the same suggestion. I'm going to get down to the marina this week and disconnect the hoses, start the engine and see if I'm getting any water through. I'm also going to see if I can blow through the exchanger.

Luckily I've got easy access!!

I've never had a problem with a water heater before so I didn't know where to start checking for possible problems.

Wish me luck!

[teshannon]

Julie,
Ditto what Art says and good luck.

[RAGTIMEDON]

Most common water heater arrangement is that engine cooling water/antifreeze mixture goes from the engine to a coil in the water heater, then to the heat exchanger, then the pump, then back to the engine. Salt water (or lake water) comes in the thru hull, to a screen filter, to the other pump, then to the heat exchanger, then the waterlift muffler, then out. Theory is that the water/antifreeze mixture heats as it the engine is cooled, the heat then goes to the water heater where some of the heat is lost for benefit of your shower, then in the heat exchanger the rest of the heat goes away so the antifreeze can cool the engine again. If your heat exchanger is plugged up, your engine will overheat. But if your thermostat is defective, your engine will take a long time to come up to operating temperature, thus your water heater will not have a hot engine to heat up your shower! Therefore, before you spend a lot of time and effort cleaning the heat exchanger, take a peek at the engine temp gauge - it may be that a new thermostat or radiator cap is the first order of business! By the way, regarding plugged heat exchangers - a wise sailor once told me that once a year you should look at the rubber impeller in your salt water pump. If it looks perfect, throw it away and put in a new one! What he meant is, replace it before it fails, so you don't have to take the pieces of a disintgrated impeller out of your heat exchanger. On my boat that is especially good advice, since my heat exchanger is nearly impossible to reach. First time I cleaned it, it took 4 hours!

[MIKEMCKEE]

When you open up your heat exchanger, run some shiskbob sticks through the tubes, this might clear out the junk that gets in there, also make sure your zink on the exchange is good.