When the Thetford doesn’t flush,it can be a challenge to find the problem.

Submitted: Wednesday, Jan 16, 2008 at 05:38
ThreadID: 124344 Views:3265 Replies:4 FollowUps:1
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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

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Reply By: Noosa Fox - Wednesday, Jan 16, 2008 at 07:13

Wednesday, Jan 16, 2008 at 07:13
Glad to find that I wasn't the only one to have a problem in that area. I was smiling to myself as I read your report thinking back to all the things I had to do to find my fault.

When or if you have to remove and replace the pump (very expensive item too) you need some shrink wrap around the cable before you join it to the old wire as there is no way of removing the wire back to the switch, and the join has to be made in where the flush water is.

As you said, very clever of Thetford to design it that way.

Brian
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AnswerID: 574022

Reply By: TroopyTracker - Wednesday, Jan 16, 2008 at 07:17

Wednesday, Jan 16, 2008 at 07:17
Neil, I know your pain.

I spent best part of half a day a year or so ago getting at those little switches. I replaced the main one with the one that doesn't let you flush with the cassette out.

That one died afew months later. I have been avoiding fixing the thing for over a year I guess, though as sale is imminent, I coughed up the $40 DOLLARS for a replacement switch and spent another couple of hours putting that one in.

You'll be glad to know that the new model (any BT's a year or younger would probably have it) is much easier to get to apparently....

I'm actually glad you found it as frustrating as me as I thought I was going to take to it with a sledge hammer at several stages...

Cheers

Matt

AnswerID: 574023

Reply By: Turist - Wednesday, Jan 16, 2008 at 17:37

Wednesday, Jan 16, 2008 at 17:37
Most times Thetford flush pump failure is due to hardened algae jamming the pump.
Continued efforts to start the pump can result in a blown fuse.

The pump can often be repaired by removing it and with the aid of a pointed tool, work at the impellor until it becomes free to rotate.
I have had to do this several times and it is a time consuming difficult job.
Just the location of the retaining screw gives problems, aligning the components while re-fitting the screw is frustrating.

But there is another answer.
Whitworths and other marine shops stock a small in line pump made by Whale.

One of these pumps will fit in the cavity where the Thetford pump goes.
No need to use the Thetford retaining parts, just let the pump sit in the bottom of the cavity.
The pump can be easily lifted out for cleaning should this be required.
Heat shrink on the cable joints will waterproof them.

And the other benefit, at about $50.00 it is 1/3 the price of the Thetford original.

As for the pump activation switch, well if mine acts up again I will fit an external push button switch, a fairly simple job.

Bob
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AnswerID: 574024

Reply By: Deleted User - Tuesday, Jan 22, 2008 at 07:52

Tuesday, Jan 22, 2008 at 07:52
mate as I am starting to spec up a new van, you are not leaving me with a warm feeling with regards to vaccum toilets
Would it be fair to say if you had youre time over again you would not go for one of these ? Regards the battler
AnswerID: 574025

Follow Up By: Bobrovin - Tuesday, Jan 22, 2008 at 08:59

Tuesday, Jan 22, 2008 at 08:59
Battler
They are talking about the thetford NOT the vacuflush, Having had both I would recommend the vacuflush
Bob
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FollowupID: 849164

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