Bruce, The water heater is a pretty basic device. And it seems that all of them (most of them?) look and connect in a similar way.
You have cold water in, hot water out (usually cold water lower than hot), pressure relief valve, drain. The coolant in and out can be on the same side (front) or at the back (most vendors offer both models). I don’t believe that there is any difference which is in and which is out for coolant (the heat exchanger is pretty simple inside). I don’t believe you will need to purge the air from the water side of the heater. The air should come out through your taps. If in doubt, you can always open the pressure relief valve (as Josh suggested) and if the water flows you are done. The bigger problem might be purging air from the coolant side. It really depends on where the heater is located. Some boats have it located high up (well above the engine). It does not look like that from your photo, but just in case. If this is the case, you need to have a purging valve next to the heater. I have seen the heaters installed like that (in the lazarette). In that case, you had to purge the air at the heater and the engine had to be run at fairly high revs (2500?) in order to push the coolant all the way there. If the heater is at the same level as the engine, you should be able to purge the air through the normal filler cap (no additional work required; the air will escape to the overfill tank). Hope it helps Marek From: CnC-List <cnc-list-boun...@cnc-list.com> On Behalf Of Ken Heaton via CnC-List Sent: 16 May, 2019 20:12 To: bwhitmore <bwhitm...@sbcglobal.net> Cc: Ken Heaton <kenhea...@gmail.com>; cnc-list <cnc-list@cnc-list.com> Subject: Re: Stus-List Purging air from Attwood EHM6-SM Water Heater This is the best I could find: http://productimageserver.com/literature/ownersManual/35883OM.pdf<https://apc01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fproductimageserver.com%2Fliterature%2FownersManual%2F35883OM.pdf&data=02%7C01%7C%7Ced9829dc8e8648f8a3fd08d6da5c61bf%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636936487640850841&sdata=GhXd56ttgFddnJiSYFbOpjUXbU%2Fef6SB5E84IYLohlE%3D&reserved=0> Ken H. On Thu, 16 May 2019 at 21:09, bwhitmore <bwhitm...@sbcglobal.net<mailto:bwhitm...@sbcglobal.net>> wrote: Ken, that makes total sense into me. Now if I can find the coolant hoses! I'm really surprised I can't find good installation instructions! Sent from my Verizon, Samsung Galaxy smartphone -------- Original message -------- From: Ken Heaton via CnC-List <cnc-list@cnc-list.com<mailto:cnc-list@cnc-list.com>> Date: 5/16/19 6:37 PM (GMT-05:00) To: cnc-list <cnc-list@cnc-list.com<mailto:cnc-list@cnc-list.com>> Cc: Ken Heaton <kenhea...@gmail.com<mailto:kenhea...@gmail.com>> Subject: Re: Stus-List Purging air from Attwood EHM6-SM Water Heater I think you have the following ports visible in your photo: H = Hot Potable Water out of Heater to your hot water taps. C = Cold Potable Water into heater from the potable water pump. D = Drain for emptying the Heater of Potable Water for winterizing. P1 = Pressure Release Valve for an over-pressure condition caused by the electric element sticking on and boiling the contents of the Heater. If you also have in and out for Coolant so the engine can heat the water they must be out of sight on the rear? What Josh said about using the Pressure Relief Valve will bleed air our of the Potable Water section. It won't bleed the coolant loop from the engine. Ken H. On Thu, 16 May 2019 at 18:29, Bruce Whitmore via CnC-List <cnc-list@cnc-list.com<mailto:cnc-list@cnc-list.com>> wrote: Hello all, I think I probably have some air trapped in my hot water heater. I have found some pretty cryptic instructions for the heater, but: a). They do not include a good drawing or explanation of how the hoses, either fresh water or coolant should be connected (yes I have looked for better online instructions to no avail) b). They say "Bleed air from the entire coolant system for proper operation of both engine and water heater", but don't give instructions as to the best way to do it. c). They do not include a listing of the what the stamped letters next to the outlets mean. (the upper left in the photo is "H", bottom left is "D", upper right is "P1" and lower right is "C" Here's a photo of the water heater: Attwood EHM6-SM Water Heater.j<https://apc01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.dropbox.com%2Fs%2Fzknhmh77qlh7ks6%2FAttwood%2520EHM6-SM%2520Water%2520Heater.jpg%3Fdl%3D0&data=02%7C01%7C%7Ced9829dc8e8648f8a3fd08d6da5c61bf%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636936487640860852&sdata=qCiuSEDrVLoDekOAIR7UpqlPRhSpOQqZLEzLSFDqvAE%3D&reserved=0> The tube in the upper left feeds the boat with hot water. I think the tube on the bottom with the valve on it comes from the engine hot water feed. I turned off the valve, and the hot water continued to run, so it is definitely not the fresh water supply line to the heater. And, having a valve on the hot coolant input line would make sense. Therefore, am I correct in thinking the pipe on the lower right would be the return coolant line to the engine? Now for conundrum #2. Here's a photo of the hoses leading out of the engine. Hot water heater hoses at engine.jpg.<https://apc01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.dropbox.com%2Fs%2F24pbeb82hakwxvd%2FHot%2520water%2520heater%2520hoses%2520at%2520engine.jpg%3Fdl%3D0&data=02%7C01%7C%7Ced9829dc8e8648f8a3fd08d6da5c61bf%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636936487640880868&sdata=jyEuqRxamoWjcRRkb0K6ISFgfohrwyGirs35jvhJHd0%3D&reserved=0> Those hoses connect to the grey solid pipes shown in the previous picture, somewhere under the floorboards where I can't see which is which. They were disconnected, but filled with coolant when I got the boat, so I was just guessing when I connected the hoses to the engine. In looking at the Yanmar manual, it appears the red hose should be the suction side coming from the water heater, and the black hose would be the pressure (hot) water coming from the engine to the water heater. Am I correct? Any way about it, since the water going down to the heater must flow down under the floorboards, up to the heater, then out of the heater and back down under the floorboards, the water heater would be a prime spot for air to get trapped. So, I am thinking I should ease off the connection coming off the lower right side of the heater and apply pressure to the appropriate hose coming off the engine, and see if I get any air out. Then, I want to ensure I am connecting the correct hose to the right inlet/outlet point on the engine. Does this make sense? Thanks for your insights! Bruce Whitmore (847) 404-5092 (mobile) bwhitm...@sbcglobal.net<mailto:bwhitm...@sbcglobal.net> _______________________________________________ Thanks everyone for supporting this list with your contributions. Each and every one is greatly appreciated. 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