Thetford in their brilliant engineering make everything almost impossible to get at to test. Theoretically there are only three possibilities, the pump/motor, the fuse & the switch.
Pump & Motor.....To get access to the pump, you need to remove the toilet roll container first. You can then see a single philips screw that holds the pump motor in place. In a previous posting from Brian Fox, there was a possibility that the pump may be jammed with some ‘gunk’. No, the pump impeller could be rotated easily with a tooth pick. Testing to see if there is any power to the motor is not easy. I have a set of probes on my multimeter that have very sharp points. I stripped back about 10mm of sheathing on the motor cable (above water level) & pierced the conductors with the points of the multimeter probes, & checked for voltage when the flushing knob was pressed. No voltage, so next, checked the fuse (Should do this first) which also was OK. The sheathing of the motor cable was then sealed with electrical tape.
Fuse...... Depending on the age of your Thetford there will be a 3Amp blade fuse for later models, or a 3Amp glass fuse in a black screw-in fuse holder in the older models. This is visible on the roof of the Thetford housing after the cassette is removed.
Switches...... It is helpful to know how this works to understand what the possibilities of why it doesn’t work. This assembly consists of two switches in series with the above fuse. One switch activates the pump motor when you press the flushing knob. The other switch opens when the cassette is removed so that you cannot flush without the cassette.
Here’s where the fun starts. You need at least the following :- Philips screwdriver with a blade at least 150mm long, Long-nose pliers, Philips screwdriver with an overall length (blade & handle) not more than 150mm long, A Col light or similar fluorescent and a swivel mirror so you can see what you are doing. A set of long arms would also be an advantage. Thetford in their engineering genius have made this bloody difficult!
First, remove the round plastic plug in the centre of the flushing knob. Use the long philips screwdriver to undo the screw down the hole in the centre.
Next, with the cassette removed, remove the white plastic 2-pin plug. You can now see two of the four screws you need to remove to get the switch assembly out.
You need the mirror to locate the other two screws, & to begin your test of patience in finding these screws & then getting the screwdriver engaged to remove them. (These are stainless steel screws, so a magnetic tipped screwdriver is no help.) A ratchet screwdriver is an advantage.
If you don’t give up in frustration, you will be able to remove the switch assembly. This also contains the mechanical linkages to open & close the blade of the cassette.
Once this assembly is out you can then check the electrical & mechanical functions of the switches, & see what needs to be replaced, or repaired.
I found the switches OK electrically, but a simple mechanical problem on the cassette switch arm which was not contacting the cassette blade-opening knob. A slight tweak with the long-nose pliers & we’re in business.
The fun really starts now getting it all back together! I still can’t find one of the holes to put the last screw back in. I know approximately where it should be, but it’s gone!
So if you have a problem with the Flushing, you have infinite patience, ½ to a day to spare, I hope I have provided you with some points to follow to find your problem
Good luck
Neil
