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Thetford C4 toilet help please!

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Can anyone tell me how to identify if my Thetford C4 is pre or post June 2000? I need to get a new seal as the current one is leaking A LOT. I'm not sure if that's because they're old or the wrong one has been used?

I've googled and googled but come up blank. My local motorhome kit shop couldn't tell me. 

Any tips would be much appreciated.

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From the FAQs here:


it would appear that Leisureshopdirect can identify the correct seal from the toilet model number (normally on the floor of the cassette opening).

If you have that identification it might be worthwhile raising a question with them.

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Take this under advice, but the Thetford spares site appears to illustrate significant differences to the blade mechanism of the pre- and post-2000 C4 cassettes. If (as is likely) it's the cassette seal you need, then that might help.

The pre-2000 version is A, the post-2000 is B.

The most immediately noticeable identification is that the newer version has the rotating circular disc as part of the closure mechanism - it swivels across and rises to block the aperture. The older version has a blade that simply slides across and has no circular disc.

It will be that difference that dictates the different lip-seal.



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This Thetford link has comprehensive information about the C2-C3-C4 toilets and the Repair Instructions include advice on cassette lip-seal replacement.


This extract shows the lip-seal replacement procedure for C4 cassettes produced UP TO 15 June 2000


and this extract shows the procedure for C4 cassettes produced AFTER 15 June 2000


The Thetford Part Numbers for the lip-seal are 16175 (UP TO 15 June 2000) or 23721 (AFTER 15 June 2000) and using the appropriate Part Number should ensure the correct seal is obtained if ordering is done on-line.

As Robinhood mentioned, the opening/closing mechanism of pre-15 June 2000 cassettes has a sliding 'blade' (and a 16175 lip-seal), whereas the opening/closing mechanism of post-15 June 2000 cassettes has a round disc (and 23721 lip-seal) that moves under the the seal and rises up to close the cassette.

(I also THINK the cassettes are interchangeable and it's when the cassette was made (pre- or post- 15 June 2000) that matters where the lip-seal is concerned, not the C4 toilet itself.)

My first motorhome was a 1996-built Herald Templar with a Thetford C4 toilet and the cassette had the sliding 'blade' mechanism. This had a notorious reputation for sticking momentarily, then fully opening abruptly and, if the cassette had positive pressure in it at the time - which was often the case - the cassette's contents could blast upwards like a volcano. Once experienced, never forgotten! (The cassette has a pressure-equalisation valve that ought to prevent this happening, but it was unreliable.)

This photo shows the entrance to my Herald's toilet-cassette locker and it will be seen that I had fitted a vent-tube arrangement (arrowed in red) to the cassette's cap to guard against  such events. (I also think the label on right of the photo may carry the toilet's date of manufacture.)


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