Temporary solution for leaking water boiler

[lavaspin]

All yea experts, can you confirm my plan to temporarily deal with a leaking boiler while I'm cruising on a new (to me) boat? I'm on the shakedown cruise and things are shaking down that weren't a problem in port, wouldn't you know.


The Quick Nautic Marine B3 water boiler on this sailboat has started leaking, probably corrosion from failure to replace the anode, and then using the engine the last few days forced the leak. I'm currently managing the leak by keeping the water pump off, which seems to release the pressure enough to slow the leak quite a bit. Based on my online research, I think I can assume the boiler is toast and there's no easy fix to the leak. This type of boiler has stainless on the inside but poly on the outside, so difficult to see what's going on.



While I've sailed a lot, I'm new to boat ownership and fixing systems. My thought is to get some right sized pipe at a hardware store, when I can find a store, eliminate the boiler, and simply connect the cold and hot engine hoses to each other, and then connect the cold and hot potable water hoses to each other. Anyone see a problem with that?



I guess I need to attempt to capture the radiator fluid when I start cracking open the heat exchange hoses? Or, maybe better to drain the radiator fluid from the engine first?


While I'm not enjoying sponging every hour or so in the back of a locker, I don't want to create a worse problem that could jeopardize the cooling system of the engine.



Finally, I have to say, I haven't even noticed hot water from the system, even though I've run the engine a fair amount for a few days, and I can feel the exchange pipes are hot. Perhaps because I'm being extremely conservative with water use (because the watermaker is also on the blink), and it hasn't made it to the faucet. But hard to imagine on a 35' boat. But the reason I mention this, am I missing something in the system that the owner might have shut down? I haven't seen any valves but there's lots of DIY unmarked stuff going on in difficult to reach places and very difficult to trace the hoses.



Many thanks in advance to the many knowledgeable folks on this forum who share their wisdom. It's a really great resource. Cheers!

[cal40john]

I think you are better off blocking off the ports. You're bypassing the engine's heat exchanger without extracting heat that the heater would normally do.

ports closed before adding a heater

water flow direction

From this thread link

[jamhass]

What John said, but also plug or bypass the fresh water side too. Bypassing the engine circuit can save your engine, bypassing the fresh side can save your fresh water supply.

[lavaspin]

Originally Posted by cal40john

I think you are better off blocking off the ports. You're bypassing the engine's heat exchanger without extracting heat that the heater would normally do.

ports closed before adding a heater

water flow direction

From this thread link

Excellent information. Thank you so much for providing these links!


Although, for a temporary fix, I don't understand why it would not be okay to simply connect the hot and cold engine hoses to each other that were previously attached to the water tank. And then do the same for the potable water hoses. Then, when I get a new boiler, I'd just de-couple the hoses and attach to the new boiler.

[lavaspin]

Originally Posted by jamhass

What John said, but also plug or bypass the fresh water side too. Bypassing the engine circuit can save your engine, bypassing the fresh side can save your fresh water supply.

Thanks! Yes, my plan had been to bypass by simply connecting the hot and cold water hoses together as a temporary measure. Cheers!

[cal40john]

Originally Posted by lavaspin

Excellent information. Thank you so much for providing these links!


Although, for a temporary fix, I don't understand why it would not be okay to simply connect the hot and cold engine hoses to each other that were previously attached to the water tank. And then do the same for the potable water hoses. Then, when I get a new boiler, I'd just de-couple the hoses and attach to the new boiler.

Put a plug in each hose instead of connecting them together.

Your way is adding a relatively unrestricted path where some of the hot water from the engine goes back into the engine without cooling. It is not going through the heat exchanger that cools the water before going back into the engine.

This is similar to the thermostat in your engine breaking in the cold position. No water goes to the engine's heat exchanger. The hot water is returned to the engine and the engine eventually overheats.

Even with the water heater in the circuit which has a heat exchanger to cool the engine water and heat the potable water, some people put a restrictor in the water heater line so it limits the water flow to the heater, presumably since once the heater is up to temp, it does not significantly cool the engine water.

[lavaspin]

Originally Posted by cal40john

Put a plug in each hose instead of connecting them together.

Your way is adding a relatively unrestricted path where some of the hot water from the engine goes back into the engine without cooling. It is not going through the heat exchanger that cools the water before going back into the engine.

This is similar to the thermostat in your engine breaking in the cold position. No water goes to the engine's heat exchanger. The hot water is returned to the engine and the engine eventually overheats.

Even with the water heater in the circuit which has a heat exchanger to cool the engine water and heat the potable water, some people put a restrictor in the water heater line so it limits the water flow to the heater, presumably since once the heater is up to temp, it does not significantly cool the engine water.

Okay, got it, and greatly appreciate your response (and quick!). I was thinking of the temporary coupling as simply a longer hose in the cooling system but I see that it really is a different path. Will get some plugs for the engine at the next opportunity. Thanks so much for the assistance!

[CaptTom]

It never occurred to me that the engine jacket water loop to the water heater might bypass some cooling capacity of the engine.

But, isn't this essentially what happens after an hour of motoring, when the contents of the water heater are the same temperature as the engine jacket water?

Wouldn't that be the same as bypassing the coil in the water heater by just joining the two hoses (in and out) together?

I've had a coolant hose fail, and done exactly that as a temporary fix. I've also run many, many hours with the water heater at the same temperature as the engine, on a fair number of different boats. I suppose it could have been dumb luck, but it seems to me it would be a poorly designed system if doing this could lead to overheating.

Still, it's something to consider if I ever notice engine temp creeping up on some future boat.

[capt jgw]

The water heater helps cool the engine at first, but I would think that once the domestic water gets up to engine temp no more cooling would take place until you used some of the hot water. In other words the cooling effect is minimal. If it's just the domestic side that's leaking I'd just connect the hot and cold lines together. I did this every fall on my sailboats, that way I didn't have to fill the WH with antifreeze, just drain it. With the WH bypassed like that you still get cold water flow from the hot water taps, also useful for winterizing.
Also on some smaller engines the WH loop is part of the overall cooling system, not just a branch circuit. Block off the WH loop and no coolant will flow anywhere, causing a fast overheat. Even an air bubble in the circuit will do that.