R25 Classic Water Heater Question

[NorthernFocus]

I've got a couple of questions about the engine coolant circuit on my 2009 Cummins equipped R25. First, the manual shows the water heater and cabin heater to be piped up in series. But I'm getting cabin heat and no hot water. Even stranger is that we've had hot water from engine heat ever since we've owned the boat up to a week ago. It suddenly stopped but cabin heat still working. If piped up in series how can this be?

A secondary question is what type valves are they where coolant goes in and out of the engine? Ball valve? Needle?

 

[BB marine]

Dan, My first question is do you have hot water when on shore power? If yes ok, if no. Did you bypass the hot water heater when winterizing water system? This happens in the spring when summarizing the systems by pass forgotten.

The engine coolant normally runs in series, engine, discharge ball Valve, hot water tank in, hot water tank out, Bus heater in Bus heater out, return ball Valve and engine. If you are getting full heat at Bus heater it doesn't make sense. Any restriction would cause less heat, the coolant must full flow to dissipate heat at Bus heater and hot water tank. If you have it at one it should be at the other. You may have heat at the Bus heater but not has much as should be there. At engine coolant temperature of 110F you will feel some warm air at the bus heater but that will not be enough to heat cold water sitting in the hot water heater. If your engine temperature is at full running temperature. Example 170 F the coolant in the hose coming off the discharge ball valve should be equal temperature ( shoot it with IR gun) 170F then shoot the coolant hose returning to the return coolant ball valve you may see a decrease in temperature if you are running the bus heater fan and the hot water tank has cold water in it but it should have no more the 20 to 30 F degree differential and after a couple of hours of run time the return should be very close to the discharge. If it isn't I would check for a restriction in the system.
Checks after engine has been at full operating temperature.

Engine coolant temperature

Bus heater/ hot water heater coolant hose discharge Valve temperature (should be same as engine)if no, no flow, if yes -

Bus Heater/hot water heater coolant hose return Valve temperature (Should be close engine temperature ) if no, probable restriction.

 

[BradOwens]

Dan,
Our water heater has a discharge mixing valve to regulate the temperature of the water going out. It has a jumper hose to the cold water line and mixes in the right amount of cold water to keep an even temperature regardless of how high the temperature in the water heater gets. The advantage is that the temperature from the heating element on shore power is less than the temperature from engine heat. If you have one of these mixing valves on your boat, it could have been bumped and accidentally set to a lower temperature, or it could be faulty.

 

[NorthernFocus]

Thanks for the replies, gents. I was on the water when I posted the question without any information about the water heater available to me. Back home now.

Brian, there's nothing out of whack from de-winterizing. As I said it worked last week. My question about the valves is due to my not having seen any like them and the fact that the heater piping effectively bypasses the cooling water heat exchanger. I thought perhaps they use a needle valve to allow "trimming" the flow rate to force adequate flow through the heat exchanger. It's a really small valve with no handle. Just what looks like the head of a screw to open/close the valve and no apparent stop position. With the bus heater running there is a perceptible temperature difference between supply/return hoses. Though no flow at all until engine is at around 1500 rpm or more. And still no hot water. Strange.

The mixing valve never occurred to me and seems like the most plausible mode of failure. Alas there is no mixing valve in the system. Just a warning note in the water heater manual that when on engine heat the water can get hotter than a household unit.

So I get back to, is it possible the two heaters are piped in parallel and I've had a hose collapse/crimp or some other obstruction? I was hoping for a factory response on the piping. If none by morning I'll have to do it the old fashioned way. Which I really hate at my age...