Dismantling Thetford Toilet

[DrZhivago]

I am trying to repair a Thetford toilet. It is not flushing and I suspect one of the microswitches has failed, or it may be the pump. I need to get the fresh water tank, pump (which I guess is inside the tank), and operator switch/shutter mechanism unit out.

Has anyone done this? It is not obvious how it comes out. The first problem is getting the operator switch/shutter unit out (1st photo) ; is there a screw under that centre or can the knob be levered off upwards, revealing some method of freeing the rest of the switch/shutter unit?

Even after that, and presumably after removing the screwed-on external fascia (Photo 2) there would still seem to be quite a lot obstructing the tank from just sliding out, such as the level indicator. Is this something the manufacture banged together with irreversible plastic barbs like so much other stuff these days?

I shall be having a go at this, will report results, but any advice first will be appreciated.

 

[Dustydog]

Dr Z.
Have you checked the blade fuse at the back of the cassette? The fuse may appear okay but due to corrosion power doesn't flow.
Have you tested the electrical circuit with a multi meter?

 

[Damian]

First thing is , on the opposite side of the flush/blade operating knob is the toilet roll holder.

The pump Is under this ,pull the toilet roll holder upwards, the pump is directly under it inside the flush tank.

Secondly, the flush tank does NOT come out, it is an integral part of the toilet moulding.

Third, on the flush/operating knob, once you prise the centre disc up you will need a long reach phillips screwdriver to undo the screw in the base of the knob and connects to the blade mechanism and microswitches.

The operating mechanism is held in a saddle arrangement under the toilet bowl, access through the cassette door. This contains the blade operating mechanism and the microswitches (two of them) and the fuse.

 

[DrZhivago]

Very helpful replies . I will have a go at this tomorrow. It had not occurred to me that the toilet roll holder might be a way in.

I had found the fuse, 3A, and it was blown. I've replaced it but still no go (although it has not blown again). The electrical supply is OK (a two-pin connector). From what I can tell the electrical supply goes in series through the fuse, a microswitch for the operator push-down knob, a second microswitch to confirm the presence of the foul casette, and the pump; not necessarily in that order. The supply and fuse are OK, now to check the other components.

The fact that the fuse had gone suggests it was caused by the pump expiring. That would have been in the previus ownership, so I don't know if there was an electrical burning smell at the time. We shall see.

 

[Damian]

It is most likely that the pump has failed.
It is quite rare for the microswitches to fail.
To replace the pump, once you have removed the toilet roll holder you will need a long phillips screwdriver to undo a screw holding the pump in place in a shroud.
Remove the pipe from the pump and lift the pump out.

With all 12v power OFF, cut the cable to the pump as close to the pump as possible.
Strip back about 2 inches of insulation from the cable supply to the pump and then enough insulation from the two wires to allow them to be crimped to the new pump wire.
Make SURE you put the pump in the shroud BEFORE crimping the wires and slide a length of heatshrink over the cable, enough to cover the joint plus about 2 inches each side.
Crimp the cables then slide the heatshrink over the joint and heat with a hot air gun to shrink the cover and seal against water damage.
Put the pump back and secure with the screw, refit the flush pipe.

 

[DrZhivago]

Quite an easy job once the loo roll holder is pulled out. The pump has failed, so no need to get the shutter/flush knob mechanism out. There was plenty of lead length on the pump, and I did not cut too close to the pump in case it was OK and I wanted to put the same one back!

Funny thing though : I tested the cut end of the pump cable with a volt meter to check that power was getting through. They had used a length of twin core mains cable - brown and blue. Unexpectedly, the blue core was the positive! I wonder if someone has reversed the wires some time at a connection somewhere else in the van. I will check the rotation direction of the new pump when I fit it.

Now to find out if I can get a replacement pump to fit - this van is 20 years old.

 

[Damian]

The van may be 20 but the pump is exactly the same now as then.

https://www.leisureshopdirect.com/water/caravan-toilet/thetford-cassette-toilets/thetford-toilet-c-402c-cassette-and-spare-parts/water-pump-12v-for-thetford-cassette-toilets

 

[canveyboy]

hi i have the same problem can i bypass the micro switchs as mine are brok
en

 

[Olestokie]

Had a similar problem, fuse blown - replaced - OK didn't blow , didn't work. The issue was the fuse holder. I had to put a new holder inline ( used Maplin inline car connectors) and now have a waterproof fuse arrangement that has been OK for a couple of years. OK, its loose but a bit of gaffa tape holds it in place and its not on view.
One way to test is to use a dressmakers pin into the wire, through the insulation and measure voltages. After measure, use a good smear of Vaseline over the area you punctured to seal the hole.

 

[Olestokie]

If you can get at them to replace, the switches are only a couple of pounds from ebay ( harder to identify) or Maplin who have a smaller selection - Changed the one in my Whale water pump from the latter.