Webasto

[Russ]

As new owners, we are working thru the various systems and correcting existing deficiencies etc and the Webasto has always been a problem reportedly so we are into it now but just a simple plumbing problem. The unit itself was newly installed at Prevost in Vancouver May 2017 and the system (DBW2010) works great but the coach history reveals ongoing no heat in aft heat exchanger. This does not have a preheat engine circuit oddly enough. One loop runs fwd to the very front t-ed off to the galley and returns, the other t's off that outbound run on the way fwd and feeds down to both hot water tanks and the return comes back up and to the bath/bedroom exchanger....the one in question. It's exit T's into the common return line. That heat exchanger has zero flow. Removed it, flushed out, no issues, re and re and re and burp and re and burp and sounds like a workout program,,,decided the T on the return was back pressuring the inlet coming from the hot water tanks and halting flow with equal pressure. At some cost in skin loss and twisted fingers, swapped the T for a branch type Y thinking the exit line now blending (not T'ing ) with the suction flow of the return line would pick up the imbalance. Wrong, still no flow...return from hot water tanks is hot right up to a foot away from the exchanger and when the system shuts down, the return Y branch heats up via radiation from the hot coolant, otherwise in and out are cool. Thinking of a boost pump coming up from the hot water loop? Burp hot water tank loop? Weird since it is simple flow but I am clearly seeing trees out there. We live in the woods but there is no forest in sight. Any revelations or hey stupid, on that item appreciated. No doubt others must have seen this as it is plumbed exactly as per the Marathon layout and appears original. There does not appear to be a remote circ pump that I can locate. The Webasto in-unit circ pump may be a bit shy on output to handle those loops? Cannot isolate the hot water tanks loop as a test either, as that is where the inlet flow to that last exchanger comes from. It is a pretty simple system.

There is the standard boost circ pump in the engine coolant/heating circuit to increase flow to the driver area, all fixed and working as it should but not part of the webastard system.

Russ, 92 Xl 40 Marathon

[Gil_J]

Russ,

I'm not sure how you don't have an engine pre heat. The coolant that travels through the Webasto comes from the engine. I suppose there's just not a dedicated engine loop.

I'm not sure I'm following the coolant flow to the rear of the coach. The Webasto supply line should Y to each heat exchanger and the returns from those heat exchangers should Y to a common return. Each heat exchanger supply, between the heat exchanger and the supply Y, should have some sorty of regulating device. This is commonly a simple on and off coolant valve. BTW, not all converters installed a regulating device on the line that supplies the heat exchangers in the hot water pumps (dumb). Assuming this is how the system is plumbed, then you can only have three sources of restricted flow to a given heat exchanger or heat exchanger zone. That will be the heat exchanger itself (not likely) or the regulating device or coolant circulating pump (if each loop has its own pump).

[Russ]

Thanks Gil,
Appreciate the thorough thoughts. Installed a piercing valve on that aft exchanger today to ensure adequate bleeding, the feed line into it got hot but no exit flow still. There is definately zero air in the system. Don't think ther ever was actually. The system has three loops, one to each fwd exchanger t,ed off the main feed line and back to the common return line and one to the hot water tanks, their return line feeds the aft exchanger then goes back into the common return line. Exactly as drawn in the manual but it seems to provide a cancelling flow for the aft exchanger. It defies physics as stated by a fellow yachter who had a look and left puzzled. Thinking it would just serve to create a new loop for that exchanger making four total and be done with it. Access had me hesitating until exhausting the easy options. The ball valve application would have been nice to have to regulate things which may have worked. Prevost invoiced the previous owner thousands without resolving it. I will get back to that item after finishing the bedroom off while it is warm here, just above zero this week. I will post how it turns out. Thanks, Gill

russ

[Russ]

Webasto update, after more thought I altered the flow in the aft heating circuit from the existing "hot water tanks to aft exchanger " to,,,aft exchanger first then hot water tanks and problem solved instantly. The installation was according to Marathon original plans but they must have had the flow direction priority reversed for this aft circuit in that drawing. Anyway, all good in the heating department, bath and bedroom are nice and warm now. Thanks for all the input folks.