Hot water system stopped working from engine heat exchanger

[gspeak]

Previously our hot water system would easily heat enough water for 4 or 5 showers from running the port engine (which it is hooked up to) for 45 to 60 minutes. Now even after a few hours motoring we only get warm water that lasts a short time.

The engine is a Yanmar 3gm30f & the heating water is hooked to the fresh (antifreeze) side to the hot water system. The motor is not overheating & is running as normal. The hot water system has a loop that mixes cold with hot water on the outlet side. There appear to be no leaks in the hoses or anywhere that I have seen & the antifreeze has not dropped in level in the engine heat exchanger.

Anybody got any ideas why this would happen:

Would a stuck open thermostat on the motor cause the motor to run too cold & cause this?

Is it possible that there is a blockage or air pocket some where in the hoses?

Is the hot water system cactus? I don't know how old it is.

Any ideas is greatly appreciated. The admiral demands hot showers

Thanks in advance.

Dave

[capt jgw]

I would suspect the mixer valve. Could be stuck open allowing too much cold water to mix with the hot. Try sampling the hot water from the safety valve or drain if it has one. CAREFULLY. The water should be at engine temperature, about 180 F. That's why you have a mixer valve. If the valve is stuck you can probably disassemble and clean it.

[ramalkin]

Are the hoses leading to and away from the heater hot? If so, the problem is in the hot water heater. If not, you may have air in the lines.

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[Dave22q]

if outlet pressure is normal and no evidence of air in the lines start with the heater. if output is hot check the mixer valve

[gspeak]

Problem solved. Thanks all for your suggestions, I feel a little silly not checking the hoses from & away the heater to the motor with the motor running . Yep they were hot.

Changed out the mixing (temper) valve sourced from a local plumbing supply place. The plumber took one look at the old valve & said its all calcified & probably jammed.

Replaced with a new one & a extra lazy hose to match up the existing hoses & all is good.

Hope this helps others in the future.

Dave

[FredRyb]

I have a similar situation. The engine doesn't head the water beyond lukewarm, even after 90 minutes, but the electric heats it just fine.

I've checked the (antifreeze) lines from and to the engine. They heat up and are much warmer than the lukewarm water coming from the heater.

Any ideas?


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[GordMay]

Greetings and welcome aboard the CF, Fred.

HWT Heat Exchanger plugged/scaled? See posts 2 & 5.

[Dave22q]

If the water in the lines is hot and the water in the tank is just warm it almost has to be restricted water flow. Not enough hot water is making it to the tank. Most likely source is partial blockage in the lines or pump/impeller problem. If lucky the partial blockage would not be in the heat exchanger because the others are easy fixes.

[Lepke]

If the water in both lines is hot, then it is passing thru the tank heat exchanger without transferring heat. That sounds like scale in the heat exchanger.

[gspeak]

Originally Posted by FredRyb

I have a similar situation. The engine doesn't head the water beyond lukewarm, even after 90 minutes, but the electric heats it just fine.

I've checked the (antifreeze) lines from and to the engine. They heat up and are much warmer than the lukewarm water coming from the heater.

Any ideas?


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As the OP of this thread, as I said in post #5, our problem was fixed by replacing the mixer (temper) valve. Seems that the old one was jammed open & mixing in too much cold water. Found a replacement at the local plumbing supply shop.

Dave

[FredRyb]

Dave - your reply gives me hope. Where can I find the mixer valve? What's it look like? Thanks.


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[gspeak]

Originally Posted by FredRyb

Dave - your reply gives me hope. Where can I find the mixer valve? What's it look like? Thanks.


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The mixer valve (temper) is fitted to the hot water outlet of the water heater & is connected via a tee to the cold water inlet. The idea of the temper valve is to mix hot water with cold to reduce the temperature of the water being delivered to the taps to a below scalding temperature. It works by a wax filled valve that opens & closes to mix the hot with the cold.

Look for a valve fitted to the hot water outlet & has another hose connected to the cold water inlet via a tee fitting & then another to the hot water delivery hose. It is a generic fitting available from any plumbing supply store. It isn't a marine only fitting.

It is adjustable for temperature via an adjustable nut or knob, but is usually set at a default temperature that is acceptable, so no need to adjust.

Dave

[Dave22q]

If you cannot find a mixer valve it may well be that you boat never had one. Mine never did nor do I see a reason to have one. Even small children can learn to test the hot and add cold as needed.

[FredRyb]

Now I understand the mixer valve. Thanks.

Since it is external to the water heater and downstream from it, I believe my problem is different from the one that started this thread. That is, when I use electricity to heat the hot water tank, I get hot water at the tap. It is only when I use the engine to heat the water in the tank that I haven't been able to achieve better than lukewarm.

I may or may not have a mixer valve, I haven't been able to investigate yet. (Anyone know if Island Packet 45's have one?)

Someone suggested that I may have a blockage in the coolant-to/from-the-heater line. I checked that and do not have a blockage.

Someone else suggested that I might have an airlock in that same line. I carefully pumped coolant into the low end until it showed up at the high end, then connected the lines as appropriate. Ran the engine 90 minutes with transmission engaged and running 1200 rpm. Still no improvement. Perhaps a bubble snuck back in during reconnection? (My WH sits higher than the engine. That's the Island Packet design, not my choice.)

My next step will be to take the boat out Sunday for several hours of motoring at higher speed and see what happens. (Heading south down the ICW.)

Thanks for your assistance and suggestions.


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[jason902]

Originally Posted by FredRyb

Now I understand the mixer valve. Thanks.

Since it is external to the water heater and downstream from it, I believe my problem is different from the one that started this thread. That is, when I use electricity to heat the hot water tank, I get hot water at the tap. It is only when I use the engine to heat the water in the tank that I haven't been able to achieve better than lukewarm.

I may or may not have a mixer valve, I haven't been able to investigate yet. (Anyone know if Island Packet 45's have one?)

Someone suggested that I may have a blockage in the coolant-to/from-the-heater line. I checked that and do not have a blockage.

Someone else suggested that I might have an airlock in that same line. I carefully pumped coolant into the low end until it showed up at the high end, then connected the lines as appropriate. Ran the engine 90 minutes with transmission engaged and running 1200 rpm. Still no improvement. Perhaps a bubble snuck back in during reconnection? (My WH sits higher than the engine. That's the Island Packet design, not my choice.)

My next step will be to take the boat out Sunday for several hours of motoring at higher speed and see what happens. (Heading south down the ICW.)

Thanks for your assistance and suggestions.


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I would check your engine thermostat. Sounds like it is jammed open providing too much cooling for your engine and consequently never heating up enough for your water heater.

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