Force 10 water heater question

[Rick]

Just took possession of our new to us 2004 Hunter 420 CC Passage. It has a Force 10 11 gal water heater I need some help with. It wont make hot water while under engine power. Warm barely.
Things I checked.
It makes hot water on shore power so the element seems to be ok.
There are no leaks or clogs in the ships cooling system that I can see. Motor temps all normal (170 F) at cruise RPM.
Coolant system serviced before survey.
Is there a bypass valve on the 420 that controls coolant flow to water heater that I have missed?
From memory, I am pretty sure I have a TCV valve on the return line at heater. Can they fail or be checked?

Any help would be appreciated.

Rick

 

[DougM]

There may be an airlock in the cooling system line from the engine.
The other possibility is that for winter storage, the coolant line and return may have been totally disconnected from the water heater and joined together to bypass it.

 

[spadaforaj]

I have the same problem - next step for me is try to bleed out any air in the lines. Also, my coolant reservoir tank is bone dry - and it's in a very awkward position to re-fill - any suggestions ?

 

[kappykaplan]

Also, my coolant reservoir tank is bone dry - and it's in a very awkward position to re-fill - any suggestions ?

Turkey baster? Large syringe?

 

[Hello Below]

Also, my coolant reservoir tank is bone dry - and it's in a very awkward position to re-fill - any suggestions ?

Utility pump.
Multi - Use Transfer Pump

 

[jssailem]

A funnel with a long hose.

 

[Hollyberry]

If path of the hoses to/from the heater creates a 'high point', you could insert a radiator drain fitting at that point to vent the air out. Our HW tank is quite high in the boat, and the reservoir is elevated above that but I still had an airlock at the heater. Venting it as described cleared things up.