Thursday, July 21, 2011

Thetford C250 cassette that will not flush ?

Never assume that it's the pump. It's protected by 3 amp fuse accessed after taking out the cassette. Thetford site shows unit upside down to indicate fuse position. Replace and your problems SHOULD be over. However if this is not the case then remove toilet roll holder and unscrew 1 clamp screw and lift pump to turn it over. It should rattle if it's free. If not then tease it through the hole in bottom. A little cooking oil will lubricate it. If this too fails then go to a motor factor with the broken pump and ask him to supply as near to it as he can. This will be a screen washer pump. You will also need to purchase heat shrink joints to rewire. Will be £££s cheaper than C2 pump. Currently £49 !!

I had the NO FLUSH issue, I first checked the fuse, then the pump, had a seized impellor that was it fixed easily. The vehicle was stored for 3 months.

Hi there i might be able to help as i am having the same problem. As you are looking at the loo there is your loo roll holder on your right! take this then twist the cup out, there you will find your pump! please make sure you have emptied your loo first.(speaking from experance). If you can cut the wires making sure you leave enough to connect them later. un screw the screw to release the pump then connect it to a 12v battery if it does not buzz then you know thats ya problem.Dont be fooled into thinking you have to buy a thretford part, you can buy of the shelf pumps that work just as good for £11.99., hope this helps you out.

A fairly easy way to do this (on the C2/3 model is to check the fuse (under fixed shelf with the waste tank out) this is a small round holder that unscrews, replace if needed, then remove the loo roll holder as it just pulls out, use a torch and pull off the large tube to the top of the motor, you should see a cross head screw, undo this and remove the pump by pulling the wire out. Hold the motor, and pruss the flush button, if you feel the motor jump a bit in your hand you have a duff pump. Before replacing it, turn it uver and you should be able to put a small screwdriver into the bottom and turn it (no direct screw hole, but you can push the vanes), turn it a few times, then press the flush again, if the motor spins, replace it, refit the screw and flush pipe and test. Took me about 20 mins! thanks to this forum, but the info in this posing is set out in several places. Hope this helps.


My c2 had same problem. Pulled pump pressed pump sw and felt motor trying to turn. impeller hard to turn but after several revolutions by hand go motor to turn slowly added olive oil to impeller area continued hand spinning and got it going. Saved mega $$. thanks


Problem whilst on holiday last week. Thetford loo would not flush. Checked wiring,fuses and switches with cassette removed and ok but motor would not turn. Went to a caravan shop for new fuses to try and luckily, their fitter was in the shop. Spoke to him and he told me how to access pump as detailed earlier. I had visions of stripping down the washroom to access and was making contingency plans to use the shower head to flush the loo as a temp measure. Apparently it is a common fault and usually cured by draining the tank, easing the pump from the tank, not pulling on the cable, and spinning the vanes on the impellor. It is suggested elsewhere, to lubricate the pump with WD40 but this is a mineral based product that can actually rot rubber products and would be better advised to lube useing vegetable cooking oil. While you are at it, put a drop or two around the seal of the cassette unit and work the sealing flap for smooth operation.


A thought or two for Arthur. Have you checked the operation and wiring to the second microswitch which is an interlock to prevent the pump from flushing when the cassette is removed. This is visible when you remove the cassette and look up to where the blade opening knob slides in. There is a microswitch up there which rotates every time the blade is opened which flexes the wires. Mine eventually broke. As a new loom is circa £20 and fiddly to get too I just by passed this microswitch and make sure no one flushes the loo when the cassette is out.

If this does not work I suggest that you disconnect the wiring to the pump and connect it directly to 12v. This will at least tell you if the pump is burnt out before you spend circa £30 for a new pump.


Have you checked the fuse which is usually visible when you remove the cassette?
You have refitted the cassette as the unit will not flush with the cassette removed as there is an interlock preventing this.
The wiring broke on my unit where the interlock microswitch is. Check this by removing the cassette looking up to where the rod is for opening the blade valve and ensure the wires asr still connected. Lastly if this all seems ok you can get to the pump by removing the spare toilet roll holder, taking out the "pot" its in and below is the pump. Try gently tapping this whilst operating the pump switch. If this fails remove the pump a philips type screw holds it in place and try rotating the small rubber impellor. Hope this is of help.

max