boat: heater blows fuses constantly.

[Pol Anorl]

boat heater (similar to a cars)

turn the switch on and nothing happens, continuity shows a full circuit but whenever i put a fuse in it and turn it on it blows instantly, went up to 30a fuse from 15 and the fuse gets hot but still no go.

most of the wiring is around the switch + the heater itself, 2 wires come off of it and go down under the boat in the tiny crawl space.

Any ideas?

it looks pretty new and no corrosion anywhere.
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[mudcow007]

something failed an giving a massive resistance hence the popped fuse?

this of any use?

[Islander]

You have a short circuit in the wiring or a damaged element or switch in the heater. It may even be wired incorrectly. Either way, something is presenting a far lower resistance than it should - what you read as a 'full circuit' is probably a short.

By the way, if you have a fuse blowing constantly never ever replace it with one of a higher value. That's one of the ways that electrical fires start. Find the fault, don't try to bodge around it.

[Nb]

Put a bulb (appropriately rated) across where the fuse goes and unplug wires until it goes out, which should help work out what area the short is in. Bet its the motor.
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[Pol Anorl]

fuse at higher rating wasn't for a permanent fix it was to see if by chance a fuse of a too low rating was fitted.

thanks for the tip about the bulb and i agree i bet its the motor, its an £800 heater too!

thanks for the link on the other guy having the same problem.

its a pain because the heater is buried!
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Jewlio Iglesias: You live in Liverpool - Chances are, the front door has already been kicked off the hinges

[Taught2BCauti...]

Try substituting the fuse for an ammeter, so you can see exactly how much current it is drawing, then check agains manufacturer's specifications.

A cheap multi-meter probably won't be much good for this though, you will need one with a 50A range and circuit protection.

It could also be a surge that is causing the fuse to blow - if the ammeter shows this, you could try an 'anti-surge' or 'slow-blow' fuse.
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