Buderus 0U error (low water pressure) — how to refill and fix

Your Buderus boiler displays error code 0U. This means the water pressure in the heating circuit has fallen below the minimum threshold (typically 0.8 bar). It’s one of the most common codes, and often fixable without a professional visit.

What does 0U mean?

Code 0U means water pressure in the central heating circuit is too low. The boiler goes into lockout to protect the pump and heat exchanger from dry running.

Symptoms

• Boiler stopped, won’t restart
• Pressure gauge in the red zone below 1 bar (usually shown as a dial on or near the boiler)
• Cold radiators across the property
• Gurgling or bubbling noises in radiators (air in the system)

Affected models

• Buderus Logamax Plus GB125, GB132, GB172
• Buderus Logano G125, G215
• Most modern wall-mounted Buderus boilers

Most common causes (in order of probability)

• Natural pressure loss — circuits lose ~0.1 bar per year through joints and air release. Refill typically needed every 2–3 years.
• Recent radiator bleeding — every bleed lowers pressure.
• Expansion vessel failure — loss of nitrogen pressure destabilises the circuit.
• Micro-leak somewhere on the circuit — safety valve, a joint, a radiator connection.
• Faulty pressure sensor — rarer, mostly on older boilers.

How to refill (quick step-by-step)

Most Buderus boilers have a filling loop beneath them — usually two small taps linked by a flexible grey hose.

1. Slowly open both taps on the filling loop
2. Watch the pressure gauge — aim for 1.5 bar (cold)
3. Close both taps as soon as pressure is reached
4. Bleed radiators (vent valve on top of each radiator)
5. Top up again if pressure dropped after bleeding

If pressure drops again within days: there’s a leak to locate — call a professional.

Typical Luxembourg intervention costs

Simple refill: no cost if you DIY. If a leak is detected, common repairs:

• Expansion vessel replacement: on request
• Safety valve replacement: on request
• Radiator joint repair: on request

Frequently asked questions

Why does pressure drop on its own?

Normal loss ~0.1 bar per year through micro-permeation at joints. If loss is faster (multiple times per year), there’s a leak.

I just refilled but the boiler still shows 0U — why?

Some models require a manual reset after pressure refill. Press and hold the reset button for 3 seconds.

Pressure rises a lot when the heating runs — is that normal?

Yes, pressure rises 0.5 to 1 bar between cold and hot. The expansion vessel absorbs this swing. If the rise exceeds 2.5 bar or trips the safety valve, the expansion vessel is probably failing.

Need an English-speaking heating engineer in Luxembourg?

Weber & Fils is certified on all Buderus boilers in Luxembourg (Logamax Plus GB125, GB132, Logano G125) and stocks the most common parts. Their technicians speak English fluently.

For quotes and emergency call-outs: weberetfils.lu/en or call +352 20 60 22 22 — 24/7.

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