How to install a Geberit Sigma button on an old Delta UP100 frame: personal experience

In short: what needs to be done

To install a modern Geberit Sigma button on an old Duofix Delta UP100 frame, you need to replace two parts inside the tank: the flush lever rockers (art. 241.829.00.1) and the water supply valve mount (art. 240.923.00.1). The Sigma button frame itself is screwed to the tank edge with 3 mm screws — the standard Delta frame mounting won't work. You don't need to touch the tank itself, the drain, or the water supply.

Task: install a Geberit Sigma button on a Delta UP100 frame

I faced a task that seemed impossible at first glance. A client's apartment purchased from a developer had a Geberit wall-hung toilet frame installed — the building was constructed about 12 years ago, and at that time Geberit's Duofix Basic UP100 (Delta) series was current. The customer wanted to install a modern flush button from the Sigma series.

I visited every plumbing store in Tallinn I knew of and got the same answer everywhere: the new system is not compatible with the old one. Formally, that's true — it's not compatible as standard. But it can be done. Below I'm sharing my experience.

What's the difference between Geberit UP100 (Delta) and UP320 (Sigma)

Geberit has two main tank systems in their Duofix line for wall-hung toilets:

Geberit Duofix Basic UP100 (Delta) — an old budget system. Compatible only with Delta series buttons (Delta 11, 21, 40, 50). No soundproofing, with rigid connection settings.

Geberit Duofix UP320 (Sigma) — a new premium system. Compatible with a wide range of Sigma buttons (01, 10, 20, 40, 50, 60, 70, 80), as well as Tango and Bolero. Includes soundproofing, flush depth adjustment, and support for modern features like DuoFresh (odor removal) and AquaClean.

In short: UP100 Delta is old/basic, UP320 Sigma is new/premium. The internal mechanism is almost identical, they flush equally well. The main difference is in button design, soundproofing, and installation flexibility.

What's inside the tank: similarities and differences

Looking closely at the tank system, I realized: the mounting slots inside are identical, but there are two key differences between Delta and Sigma:

• water supply valve mounting system;

• button frame mounting system.

So if there's an old Delta frame installed and you want to install a modern Sigma button, you need to replace two parts inside the tank.

Part No. 1: Flush lever rockers

The first part is the rockers for the button levers. In the new version, they look different in shape, but the fasteners fit perfectly into the old tank.

Part No. 2: Water supply valve mount

The second part is the mounting for the water supply hose to the tank. The fastening slots in the old tank are compatible too.

Bonus: Replacing the water supply valve

While I was at it, I also replaced the water supply valve mechanism in the tank with the current Sigma model. This step is optional, but if the tank is already disassembled — it makes sense to upgrade the valve too.

How to secure the Sigma button frame

The only thing that doesn't fit on the Sigma button is the standard Delta frame mounting to the frame. But this is solved in 5 minutes: screw the frame directly into the tank edge with small 3 mm screws. It holds reliably, and the button snaps into place normally.

Summary

An old Geberit Duofix Delta UP100 frame is not a dead end. If this system is already installed in an apartment and you don't want to replace the entire installation (and you're right — it's time-consuming and expensive), you can get by with replacing two parts inside the tank and install any modern button from the Sigma series. Shops will tell you it's impossible — but now you know how to do it.

Frequently asked questions

Can I install a Geberit Sigma button on a Delta UP100 frame?

Yes. It's not standard compatible, but after replacing two parts inside the tank (rockers 241.829.00.1 and valve mount 240.923.00.1), a modern Sigma button fits on the old Delta frame without any problems.

What's the difference between Geberit UP100 and UP320?

UP100 (Delta) is an old basic system without soundproofing, compatible only with Delta buttons. UP320 (Sigma) is a modern system with soundproofing, flush adjustment, and support for a wide range of Sigma, Tango, and Bolero buttons. Their internal flush mechanisms are almost identical.

Which Sigma buttons fit after such a modification?

The entire Sigma line: 01, 10, 20, 40, 50, 60, 70, 80, as well as Tango and Bolero. Tested — they fit after replacing two internal parts.

Do I need to replace the water supply valve itself?

Not necessarily. If the old valve works fine, you can leave it and only replace the mount (240.923.00.1). But if the tank is already disassembled — it makes more sense to replace the valve with a current model right away.

Where can I buy parts 241.829.00.1 and 240.923.00.1 in Tallinn?

At any plumbing store that works with Geberit — the parts are special order, but not rare. You can also order directly through Geberit service partners.

Post your questions and your own experience with replacing flush buttons in the comments — I'll respond.