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Plumbing Issue -- Inadequate Toilet Bowl Refill following a Large Flush (In-Wall Tank) :(

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  • Jul 3rd, 2020 7:58 am
[OP]
Sr. Member
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Aug 22, 2009
581 posts
139 upvotes
Guelph, ON

Plumbing Issue -- Inadequate Toilet Bowl Refill following a Large Flush (In-Wall Tank) :(

Hi Everyone!

I have two identical toilet setups in two adjacent bathrooms (MainBath and Ensuite):


I have an issue where the water level in the MainBath toilet bowl after a large flush is too low -- it's only refills to 4" deep (i.e. barely covering the toilet outlet hole), where as the Ensuite refills to 5" deep. After flushing, an inadequate volume of water is being refilled to the MainBath toilet bowl but I can't seem to find any sort of refill adjustment within the Geberit cistern. This issue is very concerning because I can't use my new toilets until this issue is resolved, and replacing the Geberit carrier/cistern would be an enormous effort and cost since the space is completely finished. I have provided videos, diagnostic notes, and some questions below:


Videos:






Diagnostic Notes:

Toilet Bowl Refill Levels:
  • MainBath, after Large Flush = 4" (too low, barely covering the outlet hole)
  • MainBath, after Small Flush = 5"
  • Ensuite, after Large Flush = 5"
  • Ensuite, after Small Flush = 5"

The water level in the MainBath and Ensuite cisterns are both at the "fill line" within the tanks
  • Even if I force additional water into the tank past the fill line (by pressing down on the float), the MainBath toilet still only refills to 4" following a large flush
  • This implies that the water level in the tank is not the issue

I can use a watering can to manually trickle water into the MainBath bowl to increase the bowl water level from 4" to 5"
  • This implies that the toilet's S-bend is not an issue

If I do a large flush in the Mainbath and continue holding the button, it will allow some additional water into the toilet and it will refill to 5" (but this isn't normal operation)

I tried removing the MainBath actuator plate and button assembly to manually flush the toilet by pulling up on the stopper
  • The problem persisted -- the bowl would only refill to 4" following a large flush
  • This implies that the length of the buttons is not an issue

It seems that the MainBath water level will refill to 5" after a small flush, but only fills to 4" after a large flush:
  • You can see it in the video, but the MainBath toilet has a loud "gurgle" sound at the end of the large flush (since the toilet bowl pretty much empties entirely); the Ensuite toilet doesn't do this
  • Since the MainBath toilet empties completely during the large flush, it requires more water to refill the bowl compared to the Ensuite toilet; however, the toilet bowl refill ends after the same short duration for both toilets (which I believe is why the MainBath only fills to 4" instead of 5")
  • When doing a small flush with the MainBath, the bowl doesn't empty entirely (so I think this is why I don't have the water-level issue after a small flush)


Questions:

1.) Any ideas on what could be causing the issue? :)

2.) Standard toilets have a refill tube/hose that discharges water into the overflow tube for a period of time following a flush. How does the Geberit refill the toilet bowl? How can I adjust the refill rate so that the Geberit matches the refill requirements of the toilet?

3.) Is the sound (of complete water discharge) at the end of the MainBath flush "normal", or should it be quiet (i.e. not completly discharging) like the Ensuite?

Thanks!
8 replies
[OP]
Sr. Member
User avatar
Aug 22, 2009
581 posts
139 upvotes
Guelph, ON
Thanks :) I've wondered about the venting as well but the plumbing inspector was pretty thorough with the roughins and didn't have any concerns. And if the venting was an issue, wouldn't I have a problem with both the small flush and large flush? The water level in the MainBath bowl is stable (i.e. it doesn't shift/move with the wind and isn't being sucked back into the drain) and the flush seems powerful -- it's just not refilling the bowl with enough water following the large flush.
[OP]
Sr. Member
User avatar
Aug 22, 2009
581 posts
139 upvotes
Guelph, ON
Any plumbers out there with ideas? I'm still stumped by this one :(
Newbie
Jun 29, 2020
2 posts
Hi! I know this is an old thread, and unfortunately I don't have your answer, but I have a similar problem and was wondering if you ever solved your water level problem..

Cheers,

Randy from Owen Sound
[OP]
Sr. Member
User avatar
Aug 22, 2009
581 posts
139 upvotes
Guelph, ON
Hi Randy! I never was able to fix the problem, and I tried a lot of things (even replacing the flush mechanism and other parts in the tank). It’s been a year though and neither toilet has given me any problems whatsoever — not even a clog. They flush extremely well!
Deal Fanatic
Nov 21, 2013
6093 posts
4393 upvotes
probably venting issue. Is this toilet located in the basement? Also low water pressure could cause this, if the tank take a long time to fill after a flush

Note that I am not a plumber ;)

EDIT: I think that a venting issue would cause the toilet not to flush properly, would not cause your issue...
Deal Addict
User avatar
Oct 14, 2010
1460 posts
896 upvotes
Barrie ON
The overflow tube, inside the tank, serves two purposes.

The first purpose is to prevent the tank from overflowing in the case of a malfunctioning fill valve (e.g. the float gets stuck and water continues running into the tank). The excess water will run into the tube, down into the bowl, and when the water level in the bowl becomes higher than the top of the goose-neck , it will run down the drain.

The second purpose of the overflow tube, is that water is deliberately put down the tube, in order to fill the bowl after a flush. This task is competed by connecting a small rubber tube from the fill valve, into the opening on the top of the overflow tube.

Depending on the manufacturer of the fill valve, different techniques are used to control the amount of water allowed into the bowl, Some valves simply push water into the overflow tube for the entire time that the tank is refilling. In most cases this will put more water into the bowl than is required, and the excess water goes down the drain. Other valves have a way of controlling the flow of water through the small rubber tube. The owner adjust the amount of flow, so that the bowl will just reach the proper level as the tank becomes full and shuts off the fill valve. One example of this is in the video below. I have seen other brands make use of a roller inside a plastic wedge that pinches off the tubing as the roller is moved (similar to controlling flow in an IV drip).

All of these methods means that the amount of water flowing into the bowl is identical after every flush. The problem occurs because the amount of water removed from the bowl is not the same after every flush. When a large flush occurs, the siphoning action of the water can almost drain the bowl completely. In fact if you turn off the water supply to prevent refilling, and then try both a small and large flush, you can see the difference in water levels remaining in the bowl..

The solution is to increase the water flow into the overflow tube, so that it provides enough water to refill the bowl after the worst case drainage of the bowl. During small flushes, the bowl will refill with more water than required, but the excess will run down the drain, and the bowl level will look properly filled.

Check this video. Setting up the refill tube is described at the 45 second mark.



Image
Newbie
Jun 29, 2020
2 posts
VifferFun wrote: Hi Randy! I never was able to fix the problem, and I tried a lot of things (even replacing the flush mechanism and other parts in the tank). It’s been a year though and neither toilet has given me any problems whatsoever — not even a clog. They flush extremely well!
Thanks for the reply!

That's good news I guess! Unfortunately the water level in mine is really really low. I haven't completely pulled it apart to check everything yet, I was hoping to find a few issues others maybe had with Geberit low water to give me ideas as to what to check. I can fix just about anything, but this is just foreign enough of a system that it's nice to have a few ideas going into the teardown!

On another note, I see you're from fairly local, and you have a Tesla! I bought a Model 3 in November and really enjoy it! After this COVID subsides I'll be back to visiting family in Guelph occasionally and it would be fun to meet for coffee and talk cars if you were interested!

Cheers, Randy :)

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