Do you have an M25 engine (or M25XP)?

The hoses for the hot water heater do not come off the lines to the heat exchanger, but rather from underneath the thermostat.

Here's some work I did on my boat showing our contorted hose distribution (different than yours).

[url]http://c34.org/bbs/index.php/topic,4518.msg26462.html#msg26462[/url]

Underneath the thermostat on top of the freshwater coolant pump.

Here's some more hot water system info, including input from Tom Soko.

[url]http://c34.org/bbs/index.php/topic,3769.0.html[/url]

Good luck, great project.

Fred and Cathy,
To be perfectly honest, there are many ways to plumb your water heater. The antifreeze solution in the cooling system is a closed loop, which gets circulated thru the engine and heat exchanger by the water pump (circulating pump) on the front of the engine. Very similar in concept to the cooling system in your car. Earlier M25 engines (on both the C36 and C34 and I'm sure many other models) had a complicated system of gate valves and plumbing near the back of the engine, under and around the heat exchanger. It was a mess. From my reading and talking with others, I gather that the gate valves were there to be able to control the relative flow of heating/cooling water between the water heater and the heat exchanger. Why? I have no idea. Most owners I know (including myself) took out the extra few feet of hoses, pipes, and gate valves, and opted for a simpler system. That is the hand-drawn schematic you see in the owner's manual in the Tech Notes CD. That is my drawing. Before that drawing there was no reference to the water heater at all!!! Because, as I said earlier, the system is a closed loop, you can "cut into" the loop at any place and add a water heater. You are simply making the loop bigger. At some time over the past 25 years, manufacturers, specifically Catalina, began the practice of tapping into the cooling system between the water (circulating) pump and the thermostat. That's what you see on most boats today. I'm sure there is some technical reason why that spot was chosen, but I don't know it. So.......there you have it. A long-winded explanation telling you a lot more than you needed to know. Long story short, find a convenient spot in the cooling system loop to tap into, get the necessary fittings, and plumb your water heater. If you use the now common spot between the water pump and the thermostat housing, you will have to get fittings going from roughly 3/8" to 5/8" (I don't think the water heater fittings are3/4"). If you use some other spot to tap into, which already has 5/8" fittings, your life will be simpler. I hope that someone else will reply to this with the reason for using the now common spot, so that I can learn something, too! Hope this helps.

Fred, you already have contributed. Be aware that the gate valve arrangement, as far as I know, was ONLY installed on Catalina 36s. Also mentioned by Tom in that link I posted before. Given my experience with my M25, I would urge you to consider the thermostat connection location. The reason? Because while Tom is correct that it is really the same "loop", you will find that sometimes you have to service the HX and sometimes the hot water heater and its much nicer to have the plumbing for them on separate loops. I don't know the reason why technically, but realistically in doing maintenance I like them separate.

You should also (actually MUST) find a small piece of small hose between the thermostat and the water pump on your engine, where I showed the heater connections. That's the 3/8" hose Tom mentioned. Mine goes from 3/8" to 5/8" in the gold fittings shown in the other link. That short hose was the way to keep the loop closed. Remember, these were tractor engines in their previous lives!

Stu,
Good point, but you have to remember that the C36 has better engine access than the C34! :)
(Sorry, I just couldn't resist!!!)

Found out just before I left Sceptre after a nice weekend that I have to replace my water heater. It looks like the water supply valve manifold and the water pump will have to be removed to allow removal of the unit but am trying to figure out how to remove the heat exchanger hoses and the hold down bracket from the rear of the WH. Does the large drawer underneath the galley sink and all of its innards have to be removed first to access the rear connections? I didn't get much time to thoroughly check out the replacement procedure so please let me know if this has been written up before and where i might find it.
Thank you,

[QUOTE=sceptre1;16704]Found out just before I left Sceptre after a nice weekend that I have to replace my water heater. It looks like the water supply valve manifold and the water pump will have to be removed to allow removal of the unit but am trying to figure out how to remove the heat exchanger hoses and the hold down bracket from the rear of the WH. Does the large drawer underneath the galley sink and all of its innards have to be removed first to access the rear connections? I didn't get much time to thoroughly check out the replacement procedure so please let me know if this has been written up before and where i might find it.
Thank you,[/QUOTE]

There is an article in the technical maintenance section located here: [URL="http://www.c36ia.com/node/170"]http://www.c36ia.com/node/170[/URL]

You do have to remove the cabinet section under the sinks in order to remove the water heater.

Hope this helps.

Thanks Ralph,
Not looking forward to the removal of the cabinitery.

[QUOTE=sceptre1;16710]Thanks Ralph,
Not looking forward to the removal of the cabinitery.[/QUOTE]

Hi Tony,

This is an easy job for sure and a must for access to the water heater. I just did the job in the fall....removed all gate valves and the cabinet to access the old water heater. Once that is done you have clear access to the heater for installation. You will see the platform where it is supposed to sit on the port side. Good luck with the install.

here is what was on my [URL="http://www.c36ia.com/forums/showthread.php?t=1566"]boat...[/URL]