Poor Toilet Flush Action

16 Mar 2004
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United Kingdom
About 2 years ago, we changed the toilet for a built in type with the flush mechanism concealed in the housing unit, as shown in the picture

The flush efficiency was never very good and in an attempt to improve this, I recently changed the pipe connecting the cistern to the pan: the old pipe coupled the cistern to the pan via a right angle bend, and the new pipe has a curved radius

With a single action to the flush lever, the water does appear to flow into the pan at a reasonable rate, and empties the reservoir completely.
However, the flush results have been getting worse and often the waste is not removed

It is possible to get the waste removed in the majority of cases, but only by doing either of the following:

a) pump the flush lever many times until the water in the reservoir is exhausted
b) pour a bucket of water into the pan

The cistern is a Thomas Dudley Ltd Turbo 88 WC Syphon

Obviously this is not satisfactory, and I am looking for any suggestions to improve this

Thanks for reading and any help
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If it is a close coupled toilet they are never very good at clearing all the pan contents! :(

Are you sure there is no blockage further down the line?
If you have to pump the lever, it usually means that the diaphram in the siphon is split or deformed.

As Carlo pointed out
Are you sure there is no blockage further down the line?

Will be observed by the pan partially filling on flush and slow to drain.

Are there any tree roots close to soil waste pipe runs, conifers are worse for this ;)
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Thanks for your replies

Interestingly, we did have a conifer close to the drain runs, but took it down about two weeks ago

However, the toilet in question is on the first floor and we have a ground floor toilet with a low level flush that works perfectly

I have never observed the pan partially filling
If the run to the drains was partly blocked, I would expect the pan contents to be removed quickly into the vertical soil pipe, but then drain away slowly at the bottom - is that a fair assumption

I should be able to get a drain rod into the vertical soil pipe at the weekend, but it might be a problem getting it around the bend to the horizontal

The split diaphragm sounds like a good thing to check, so will also do that at the weekend


do you put anything in the cistern - such as chemical cleaning blocks? it could be that something is lodged in the syphon and is restricting the flow. may even be part of a shredded diaphragm
I managed to get a look at the syphon and waste pipe over the weekend:

a) the diaphragm was intact
b) I could view the vertical soil pipe all the way down to the bend and it was clear - no blockage in that

I don't put anything in the cistern

Comparing the ground floor toilet (good) and first floor toilet (poor) the cistern on the ground floor has a fall of about 12 inches to the pan, while on the first floor, the fall is only about 6 inches

The water definitely flows into the ground floor pan much faster than for the first floor pan; also the gap under the rim is wider on the ground floor pan

Finally, the down pipe on the ground floor pan is very short into the pan, while on the first floor pan it inserts a long way

Clutching at straws a bit, but are any of these likely to be the cause

Thanks for reading and replies

The water definitely flows into the ground floor pan much faster than for the first floor pan; also the gap under the rim is wider on the ground floor pan

There, I think lies your answer. It seems more likely to be the design of the pan than any fault with the appliance. The old high level cisterns used to give a shorter, but devastatingly effective flush! Basically, the higher the cistern, the greater the force of the flush.

In your case it seems there is simply insufficient power in the flush to clear the contents of the pan, only long term solution would probably be to change the pan. Or, if as Bahco suggests, it is close coupled its likely the pan and cistern would have to be replaced as a unit. Seems with the advent of 6 litre flushes and modern pans, the idea of saving water is not effective in practice as two or more flushes are often required to clear the contents of the pan. (Another bright idea from Brussels I believe....)

If I understand the definition of close coupled, it's where the cisten sits directly on the pan and the seal is with a rubber 'doughnut'

In my case there is a short pipe that connects the cistern to the pan, with a difference in height of about 6 inches - so I guess that makes it not a close coupled pan

Hi Geoff,

Yeh that's a "Low Level" cistern you've got then. With a flush pipe connecting the cistern to the pan. One thing to try would be reattach the cistern higher up the wall, and install a flush pipe with a longer vertical run, giving you more head (so to speak) and a better flush.
Hg - Do you have a long(ish) near horizontal run to the soil stack? In my experience this can have a marked effect on how efficiently waste is disposed of. Nothing wrong with the flush, but the pipework is too flat to get an efficient siphonic action going.

I think resiting the cistern is a non starter - if the image shows correctly, you can see that the cistern is of the concealed type and sits in a unit. This was purchased as a complete package from Homebase and the pan is a "Monte Carlo" Back to Wall Pan


I do have a "horizontal" run of about 15 to 20 feet - I looked down the vertical soil pipe and as it was clear and it would be tricky to get drain rods to go from the vertical to the "horizontal", I decided not to bother, but maybe I should attempt it to be certain the "horizontal" run is clear

Thanks for all your suggestions
I'm sort of coming to the conclusion that I should buy a quality pan with a decent gap around the rim to allow the water to run into it more quickly
I would welcome some input on choosing a replacement toilet pan

There are a vast array of pans to choose from, starting at the low end with Wickes at around £59 (and possibly some even cheaper):

to Armitage Shanks at around £307:
and maybe even more expensive

What do I look for (apart from compatibility with my installation and a decent gap under the rim)
I don't want to pay £300 if a pan for £100 will do the same function

Any recommendations gratefully received

Thanks for reading and any help
Just a quick thought, the ball valve filling the cistern is set correctly? There should be a mark inside the casting on the back of the cistern showing water line when full. With these modern 6 litre flushes, every drop really does count to have maximum effect when flushing, if its not filling up to the correct level then you will not get the full 6 litres each flush.

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