The first clue was that the thermostat display was completely blank. Well, and the boat was cold, too. Some back and forth with Marinaire, the heat pump manufacturer (great customer service, by the way), disclosed that there was a fuse on the main circuit board - a fuse hidden with a blue vinyl cover. Yep, it was blown. When it was replaced, the replacement blew immediately as the fan and circulation pump tried to start. Blowing a couple more fuses revealed that the problem was the circulating pump - the pump that provides sea water to the heat pump. (It is by the chilling of this sea water that the heat pump produces heat.)
Here's the pump after I pulled it out:
|Salt water short-out|
So I bit the bullet and ordered a new pump. This one has a magnetically driven impeller - that is, there is no shaft seal. The motor drives a cup-shaped magnet; the pump body extends into the cup but has no opening. The impeller has an imbedded magnet, and is thus driven by the motor without any mechanical coupling and without a shaft seal. As you might expect, this kind of pump is more expensive. But the technology is worth it.
As a bonus, the pump body itself (the white plastic portion) is considerably larger than in the old pump, and is much more substantially made. The inlet and outlet are larger as well.
Since the pump is physically larger, it wouldn't fit where the old one had been. So there was some fooling around involved in finding a location that...
- was below the water line as far as possible - centrifugal pumps are not self-priming,
- was not actually on the floor of the bilge compartment, since that would promote rusting of the motor base,
- did not interfere with access to the nearby battery,
- minimized the required plumbing changes,
- and finally, did not block the access door you see in the background to the right.
Based on the appearance of the discharge water stream, I'd estimate that this pump is delivering twice as much water as the old one, even tho both are rated at 500 GPH.
The boat is warm! And now I expect to be able to forget about this pump for a long while, just as I have been able to with the refrigeration circulating pump.
Magnetic personality? I must have one. Can I make a recommendation here? Avoid sea water pumps that have shaft seals wherever possible. Like the cosmetic ad says, they're more expensive, but you're worth it.