Cassette flush DIY

Discovering the problem.

No flush water

Our first trip this season revealed that my checks had proved incomplete as there was no flush water coming into the cassette toilet and no sound of the pump running.

Fuse was blown

A quick call to the caravan dealer established that the bench cassette toilet fuse was an uncommon 3A purple blade fuse located inside the cassette compartment and could be changed once the cassette was removed. It’s fiddly to get to as it was mounted high up at the back end of the compartment under a small panel at arm’s length from the access door.

My multimeter showed that the fuse had failed, but why? It seemed sensible to check the pump before fitting a new fuse.

What caused the fuse to blow?

Pump had seized

It turned out that the pump had seized, which was causing an overlarge current flow to blow the fuse, thus protecting the pump motor windings. Access to the flush pump is also tricky and you need to reach it from the washroom.

Once repaired, it was refitted with a new fuse and the wiring and connectors carefully checked before running the pump briefly to confirm that no permanent damage had been done.

Same size fuze - always!

It is important always to remember to refit a replacement fuse of the same rating as this will continue to protect the wiring of the pump itself.

What caused the pump to seize?

Algae seized the pump

Returning the pump to its reservoir, I did notice that presumably because I just use fresh water for flushing, the interior of the flush tank was a bit slimy with algae.

I think that it was this that had caused the pump seizure once the tank had been drained for winter and dried out, gluing up the pump innards.

Step by step guide

Here is the complete fix in one simple 3-step guide.

Now you’ve completed all the steps, you should have yourself a perfect flush!