Stus-List Purging air from Attwood EHM6-SM Water Heater

Bruce Whitmore bwhitmore at
Thu May 16 17:29:00 EDT 2019

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
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.  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)
bwhitmore at
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the CnC-List mailing list