Public Discussion Forum

The usual focus of my writing on this forum is on the topic of reliable electronic propulsion and docking controls. This thread departs from that topic to report my recent adventures in the minutia of the oft-maligned Webasto coolant heater at the heart of the hydronic heating system aboard Alyeska (hull 47-07). If your ship has the same heater, then this report may be of interest to you.

During our recent Sep/Oct cruising in the BC Gulf Islands the weather decided rather inexplicably to turn from Summer to Winter. And, this being boating, the hydronic heating decided to become inoperative despite the loving maintenance attention that I had lavished on the system this Spring. The admiral was not pleased.

And so I set to work troubleshooting the pesky coolant heater, using Webasto's handy guide. In order to confirm that fuel supply was not obstructed I disconnected the fuel return hose at the fuel return line from the burner unit, installed a short section of clear hose routed to a waste jug, and then turned on the heater to attempt a start cycle and to confirm the flow and return of fuel through the fuel pump.

On startup the electric motor should spin the intake compressor, and a spur gear on the end of the compressor shaft should drive the fuel pump gear to spin the fuel pump to pressurize fuel to the fuel solenoid which will activate after approximately 15 seconds of fuel pump operation, and the solenoid will open to deliver atomized fuel through the (newly replaced) fuel nozzle at the same time that the ignition electrodes receive current from the ignition coil to produce flame. During the entire cycle (including cool-down after the thermostat temperature is reached or the heat switch is turned off), as long as the motor is running there should be fuel flowing through the fuel pump and back to the supply tank.

So, on this test, when zero fuel flow from the fuel pump's return line, I removed the fuel supply hose from the burner unit and confirmed the ready flow fuel on the supply side, and then reconfirmed that I could hear the motor running inside the burner unit during the cycle, but that no fuel was exiting the fuel pump.

A review of Webasto's Basic Troubelshooting reference, and further study of the official repair manual led me to the conclusion that the fuel pump had failed and would need to be replaced in order to resume heating Alyeska. Again, the admiral was not pleased.

Sure Marine provided excellent parts supply once again, and the next day after our return to our moorings I installed the new fuel pump, placed the burner unit back into service, flipped the start switch on, and... no joy. My careful review of the repair manual and expensive parts replacement produced zero improvement.

At this point I was desperate to avoid reporting my failure to admiral for further disapprobation, and so finally removed the plastic cover from the motor housing (the easiest and most accessible part of the unit to disassemble, inspected the drive motor and immediately found the source of the problem: the plastic spider that joins the two toothed couplings on the motor shaft and the combustion air fan shaft together had split in two and fallen away, leaving the drive motor to spin freely without driving anything - no fan air, and no fuel pumping.

To test my diagnosis this time I placed the two pieces of the broken spider back on the couplings and wrapped a small amount of aluminum tape around the assembly to keep the spider engaged with the couplings, reassembled the burner unit and reinstalled it with fuel lines connected. Viola! The unit was again pumping fuel as expected, and on further testing started and ran normally.

Yesterday UPS delivered to me a new coupler assembly from Sure Marine to replace the assembly that I taped together for testing. I'd be tempted to leave the taped unit in service to see how it lasts before needing re-taping or replacement, but I don't want to risk any further rebuke from the admiral. If your Webasto heater was supplied by Sure Marine it will have this three-piece Guardian-10 coupler instead of the two-piece coupler shown in the Webasto parts diagrams.

The main takeaways from this experience for me are that the troubleshooting and repair instructions in the manuals fail to call attention to the simplest and cheapest repair components, probably leading to frequent replacements of expensive parts that were not the root problem, and that just because I can hear the drive motor spinning doesn't mean than it's driving anything. Removing the covers to inspect fully before ordering expensive parts might be sound practice.

The secondary takeaway is that if you find yourself far from parts supply when your Webasto hydronic furnace fails in cold weather, it may be that you can repair it temporarily by simply removing the motor cover and taping the coupler spider back in place. Duct tape can sometimes be powerful magic.

Happy boating!

Jim

Update: The new coupler spider is now installed, and the system has been running for a few hours. Even though the fuel pump was not the cause of the stoppage before, the new fuel pump has definitely rejuvenated the performance of the heater. Before replacement, the unit would puff grey smoke (incomplete combustion) for 10-20 seconds on startup. Now, with the new fuel pump, there is only the slightest whiff of smoke for a brief second on startup and then the unit runs without any visible smoke and minimal exhaust smell. This is likely due to the new fuel pump atomizing the fuel at the nozzle more optimally for efficient combustion.

I surmise from this that the replacement of the fuel pump was justified in improved performance and longevity. (Webasto recommends replacement of the fuel pump every five years.)

Alyeska is again toasty warm. The admiral approves.

Low pump pressure results in poor atomization of fuel. When servicing oil burners, part of the setup process is to increase the pump pressure. This results in finer atomization, cleaner burn, cleaner start, and longer interval between service. Any oil burner requires regular routine service to insure the burner is firing optimally. Most service techs don't utilize the available instruments (combustion analyzer) to insure a clean burn, in particular, a CO indicator. Many use CO2 to set up, but a CO reading is more telling, as it's reading the amount of UNBURNED fuel, which leads to poor combustion, soot production, and potential premature fouling of the combustion chamber and flue passages. Rising CO numbers to any degree are bad. Setup of any oil burner without using instruments is a crap shoot. The takeaway is that if your technician isn't using instruments to properly set up a burner, you'll have a shorter service interval, and you're not getting your money's worth.

All true, though rarely if ever applied closely to the maintenance of hydronic heaters on boats.