Thetford Cassette Toilet: Common Faults And Easy Fixes

Like most things caravanning – they are not without their faults. Today we look at the most common Thetford cassette toilet faults and easy tips and tricks to fix them.

Many appliances, accessories, and upgrades have been added over the years to make living in a caravan much more comfortable than traditional camping. The cassette toilet is my favourite invention!

What Is A Cassette Toilet?

The Thetford C2 Cassette Toilet is a common mainstay in most caravans and motorhomes. They have a practical design that makes it easier to maintain your toilet and waste system in your tourer.

The Thetford C2 cassette-toilet toilet is the most popular model. If you have any problems with it, there are likely to be other users who have had similar issues. The flush not working properly is a frustrating and annoying issue that can cause problems with the Thetford C2.

Cassette Flush Not Working

What good is a supposedly sanitary toilet if you can’t flush it and dispose of your waste in the portable compartment? It’s completely useless.

We sympathise with you if you’re having trouble getting your Thetford’s flush feature to operate, and we’re here to help.

What’s The Cause Of The Fault? And How Can It Be Fixed?

It appears to be down to the fuse and the fuse housing that come with the unit when you buy it, according to several people who have had Thetford C2 cassette toilets in their tourers and have had this issue. Many users feel that these are not poorly constructed and are placed in difficult areas unprotected.

You can remove the fuse, then clean all the female parts with fine-grade sanding papers. It will be difficult, but it is worth it.

Next, you will need to purchase high-quality electrical contact spray and fully coat the housing with it. Allow it to dry, then repeat the process.

WD-40 44716 Specialist Fast Drying Contact Cleaner 250ml

WD-40 44716 Specialist Fast Drying Contact Cleaner 250ml
  • Creeps quickly into hard-to-reach areas within electrical equipment
  • Safe to use on sensitive electrical and electronic equipment.
  • For circuit boards, electrical components, printers, switches.
  • Valve allows for upright or upside down application, making every job possible
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Once it has dried again and the protective layer is intact, you can insert the new fuse and reconnect everything. It should now work as expected. The result is that the flush pump will be working again.

It’s amazing to see how often these accessories and appliances can have problems! This should resolve any problems you may be having with your cassette toilet.

Replacing The Seal On A Thetford Toilet Cassette

You may notice unpleasant odours emanating from your caravan’s or motorhome’s bathroom. Your Thetford toilet cassette seal needs to be replaced or repaired.

The ‘lip seal’ is the seal on a Thetford toilet cartridge. It is placed against the open-close valve on your toilet cassette or the toilet bowl in your caravan/motorhome.

Thetford Replacment Lip Seal

Thetford Replacment Lip Seal
  • For Thetford casette toilet C2 / C3 / C4 before year of manufacture 15.06.2000
  • Manufacturer no.: 16175
  • Comes with full instructions
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Why Are The Lip Seals Failing?

As you might expect, the rubber lip seal is made of rubber. It seals the contents and smells in the toilet cassette. Rubber becomes more flexible and less malleable as it ages.

Cracks eventually develop and the lip seal will no longer be suitable for its purpose. UV and other factors can also age rubber.

It is obvious that a Thetford toilet cassette will be kept in a caravan or motorhome for the majority of its life. This means it is not exposed long-term to the sun.

Blue toilet chemicals can have an impact on Thetford toilet lip seals. The point is that eventually, the rubber lip seal will need to be replaced.

You May Be Interested In: How To Properly Use A Caravan Cassette Toilet: Tips from Experience!

How To Repair A Thetford Lip Seal

Dan (Meet the Trudgians), from Practical Caravan, has the best video I have seen. Dan gives a detailed explanation of how to open Thetford’s toilet cassette. Then, he shows you how to take out the components and get to the lip seal.

Dan then shows you how to remove the components and replace them with seal lubricant. The video below will show you how to replace the lip seal of your Thetford toilet cassette. You will find a few additional comments from me below.

After you’ve seen the video, I’d like to add some comments to help you understand how I would approach the task.

Practical Caravan – how to replace a Thetford toilet cassette seal

First, Thoroughly Clean The Thetford Toilet Cassette

Although the video doesn’t mention this step, it may be assumed to be obvious. The point is that nobody likes emptying a Thetford toilet cartridge, let alone opening it up to fix the lip seal. Before you open up the cassette to do the work, you need to clean it thoroughly.

When I say thoroughly, I mean as if you had never done it before. You should add freshwater to the cassette, along with a blue or cassette cleaner!

The screw top lid should be reattached and the cassette should be shaken repeatedly. Next, empty the cassette and repeat the process. Repeat this process until you feel confident that you can open the toilet cassette.

Thetford Duo Tank Cleaner Concentrate 800ml

Thetford Duo Tank Cleaner Concentrate 800ml
  • Removes limescale, encrusting and grease deposits
  • Technical parts inside the tanks are cleaned as well
  • Prolongs the lifespan of the tanks
  • No scrubbing required!
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Clean the cassette thoroughly before you start the task of replacing the lip seal.

You Might Be Interested In: How To Get Rid Of Condensation In Caravan Windows

There is one caveat to all of the above. If the lip seal has been damaged or is leaking, it will be reopened. Some of the contents could escape if the toilet cassette is shaken.

You may need to seal the toilet cassette with quality duck tape/plastic bags. You could also place the entire Thetford toilet cassette in a bag. Before shaking can begin, make sure you tie the top.

Products And Tools For The Job

You will need a new Thetford lip seal. Thetford C250 and C260 toilet cassettes are standard on most caravans and motorhomes. You will likely need the C23721 lip seal.

It is best not to guess and make sure you are familiar with the exact Thetford toilet cassette and the lip seal that you require.

A suitable seal lubricant is also necessary. Although olive oil and similar products are possible, Thetford seal grease is very affordable.

Other than using olive oil to lubricate your toilets lip seals, you might also consider Thetfords Seal Lubricant Spray:

Thetford Lubricant Spray 200ml

Thetford Lubricant Spray 200ml
  • Thoroughly lubricates and protects toilet seals from drying out
  • Ensures the smooth operation of Thetford toilet valve blades
  • Safe to use on all types of plastic and rubber
  • Specially developed for Thetford cassette toilets
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You will also need a pair of gloves. To complete the job of replacing your lip seal, I recommend using good disposable gloves. Disposable gloves are what I prefer to use for emptying Thetford’s toilet cassette.

Fixing The Toilet Full LED Indicator

Many caravans and motorhomes are equipped with Thetford C250 toilet cassettes. This allows you to see an LED that indicates when the toilet needs to be emptied.

The video below by Dan offers excellent advice about how to spot a problem if you are unsure if the toilet light is on.

Fixing a Thetford C250 Cassette Indicator

Thetford C250 Float Magnet, Reed Switch

As you can see in the video, Dan first checked that the magnet in the C250 toilet cartridge was still in place by using the reed switches. Dan discovered that the problem was in the connection of the reed switches.

If you don’t have the skills to repair the problem with a soldering iron and a voltmeter, you can purchase a brand new Thetford Reed Switch.

You can order a replacement if you are unable to repair a Thetford reed switching failure from

The 3A blade fuse is the first thing you should check. It is possible to check the fuse with a voltmeter, but they are translucent. If you can see the completed S inside the fuse, it is fine. I

f the S isn’t complete or the fuse blows, you’ll need a 3A replacement blade fuse. A set of blade fuse is handy.

I have accidentally blown a few fuses while trying to fix a 12V issue in my car’s electrical system!

A blade fuse set is often very handy when it comes to fixing 12V electrical problems in a car, caravan, or motorhome. You can get a set pretty cheap here.

You shouldn’t assume that the service centre with your annual caravan service will fix your Thetford toilet cassette. You will need to take the problem to your service centre if you are unable to fix it yourself.

Remedy For Toilet Flush ‘Black Bits’

We have a more detailed post here if you experience ‘black bits in your toilet after flushing. But the video explains how the ‘black bits” issue might occur. It seems that if you flush the toilet, you find black bits may appear. This is likely due to algae growing in the tank.

Remove “Black bits” from a caravan toilet flush tank.

It seems that the black parts of your toilet tank are algae that have been eating pink toilet chemicals!!

Clean The Toilet Flush Tank

In my How to Sterilize a Caravans Water System, which also includes Dan’s video, the topic of Milton use in a caravan is covered. If you’re not comfortable using Milton – Puriclean is another of my recommended alternatives

Is there any metal on the toilet flush tank/pump? Puriclean can be used instead to clean the toilet flush tank, as Dan shows in the video. To make this cleaning process more effective, you will need to leave Puriclean in your toilet flush tank for at least a few hours.

Puriclean Water Purifier 100g for Caravans

Puriclean Water Purifier 100g for Caravans
  • Unique dual purpose formula which both cleans and sterilises in one easy action
  • Cleans the complete water system: tank, pipes, pumps, taps
  • Eradicates bacteria, viruses, biofilm, algae and fungi
  • For maximum results, simply soak and flush
  • Powerful action without harming the components in the water system
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How To Stop The Issue From Recurring

Dan shares some great tips for draining the toilet flush tank after it isn’t in use. You should also allow the toilet flush tank to ‘air out’ by leaving it open for a few minutes. Dan points out that the pink flush tank fluid can be used if you wish. It does not affect the content of the toilet cassette.

It’s really only to make using the Thetford toilet cassette in your caravan or motorhome a little more enjoyable by adding a pleasant fragrance.

This may be why it is important to use less pink toilet flush chemicals than what is recommended.

Thetford Toilet Pump Repair And Replacement

To avoid pump freezing issues, we flush the toilet flush tank each winter. A few winters back, the toilet flush tank pump failed to work when we tried it the following spring.

We also found water in the toilet cassette lock. We found that the toilet pump was still in good condition after removing it and inspecting it, but the water expanded and froze during winter, causing the seal to crack.

It was impossible to repair so we had it replaced with a new one.

For winter prep, we drain the toilet flush tank and now also take out the toilet flush pumps. It could be that the pump itself is working fine, but the control panel on top of the toilet is defective but we don’t take the risk.

How To Properly Use And Empty A Thetford Toilet Cassette

Having spoken to fellow caravanners on-site – sadly it seems that some of them had not been shown by their caravan dealer how they should properly empty their Thetford toilet cartridge.

To add to these comments, I wanted to refer to the Practical Motorhome video on how to empty a toilet cassette.

This Practical Motorhome video is my favourite for cleaning and using the Thetford toilet cassette.

Toilet cassettes – expert advice from Practical Motorhome’s Diamond Dave

Important: The Vent Button

Many first-time caravanners will have experienced unpleasantries upon emptying the toilet cassette and splashback!. Splashbacks will make emptying a toilet cassette a nightmare.

It seems that many first-timers don’t know the importance and use of the vent key. To avoid splashbacks, pressing down on the vent button and keeping it down is crucial.

Blue, Green And Pink Cassette Toilet Chemicals

I will soon write a post specifically comparing the various cassette toilet chemicals. The pink flushing chemical can be used, as we have already discussed. But there are other options for the blue chemical, as Practical Motorhome video refers to.

A washing machine bio tablet is also shown in the video. I have never tried this solution personally, so I am not sure about its effectiveness. There are also bio-friendly toilet chemicals.

Aqua Kem Blue is still my favourite product for removing the contents from the toilet cassette. However, I recognize that it is not the best product for our environment. You can get it here.

Thetford Fresh Up Kits

Thetford toilet fresh-up kits’ are available for purchase, as discussed in the Practical Motorhome video. It is basically a new Thetford toilet cassette with a toilet seat that can be fitted to your caravan or motorhome.

The fresh-up kits are especially useful for those who purchase a second-hand caravan, motorhome or campervan. The C250 Fresh Up Kit will be the best option if you own a caravan. The C200 is more appropriate if you own a motorhome.

You will likely need the C250 Thetford Fresh-up Kit for a caravan:

Thetford C250 Toilet Fresh-up-Set

Thetford C250 Toilet Fresh-up-Set
  • Fresh-up set contains brand new toilet seat and cassette tank
  • Your toilet feels completely fresh again
  • Sustainable and cheaper than a new toilet
  • Available for all Thetford cassette toilets
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A motorhome will likely require the C200 Thetford Fresh Up Kit – here

That’s all for today. I hope that you find the above information useful in fixing any issues with your Thetford toilet cartridge!

Happy Caravanning!

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