described how our tankless water heater had stopped working because the thermal fuse had been triggered. (The fuse is a single-use wire that had to be replaced and is marked by the red arrow in the picture.)
The heater itself is a marvel of compactness compared to a conventional 50-gallon tank. However the design is not conducive to an easy repair. Replacing the fuse, a $20 part, requires the removal of the entire internal apparatus. Several plumbers quoted over $1,000 for the job.
Even if the fuse was replaced successfully, there was a distinct possibility that the heat exchanger was damaged. That was an $800 part (the brass box in the upper half of the picture), and we were quoted $3,000 to replace both the thermal fuse and heat exchanger.
Some helpful contractors suggested that I simply buy a new heater at a cost of $4,000-$5,000, depending on the model. The life expectancy of a tankless water heater is 15-20 years, and even if we were to repair our 14-year-old appliance
we might have to replace it anyway in 3-5 years.
Not liking the choices I was given, and sensing that I was being ripped off by plumbers who view all Peninsula homeowners as rich patsies, I decided to take a shot at fixing the thermal fuse myself. Even if I ended up paying someone $thousands, I could see little harm in trying.
To make a long story short, dear reader, the endeavor was a partial success. I overnighted the part from the manufacturer and took apart the water heater. The work was much more involved than DIY Internet videos and instruction manuals
imply. There were dozens of connectors, screws, and subassemblies that had to be marked and sorted as they were taken out. Eventually I was able to remove the old fuse and wrap the new one around the heat exchanger. When I put everything back, the unit wouldn't start; even the error-message panel was blank. It was time to call in a professional.
I contacted a large San Jose contractor recommended by the manufacturer. The technician came the following morning. Before disassembling the unit, he decided to see if what I had done had some value. He rechecked all the connections and tightened some that were loose. He plugged in the heater, and it turned on! Hot water was back.
The technician suggested that the issue was probably a grounding wire that I had not secured properly. I was happy to pay his invoice of $275; his fee for a fuse replacement would have been $1,150. I tipped him and sent him on his way.
Meanwhile, I won't forget to scale the pipes.