Chaffoteaux 123 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 123 fault code mean?
On Chaffoteaux boilers with a two-digit digital display — including the Talia, Pigma, Inoa, and Expert Control ranges — fault codes are structured so that the first digit identifies which part of the boiler is involved. Codes starting with '1' relate to the primary heating circuit, and the sequence 1 03 through 1 07 are all documented as 'Flow Check Failed' faults. Code 123 (displayed as '1 23') sits within this same family and indicates that the boiler's internal monitoring has detected a problem with water circulation or flow in the primary circuit. The boiler will typically lock out as a safety measure. Important caveat: on certain older Chaffoteaux models, '123' is not a fault at all — it is an installer menu access code (alongside codes such as 000, 42, and 222 on different variants). If 123 appeared on your display during normal boiler operation without any button presses, treat it as a circulation fault. If it appeared after you were navigating the boiler's menus, it is likely the installer access prompt and not a fault.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Failing or seized circulation pump Common
The circulation pump is responsible for pushing water around the heating circuit. If it has seized mechanically, developed an electrical fault, or is simply worn out, the boiler's flow checks will fail and trigger a lockout. A pump that is running but delivering poor flow can also trigger this code without failing completely.
- Sludge, debris, or airlocks restricting flow Common
Over time, magnetite sludge and limescale can accumulate in pipework and radiators, significantly reducing flow rates. Airlocks trapped in the system can have a similar effect. Both problems prevent the boiler from detecting adequate circulation, leading to a flow check failure.
- Low system pressure Common
If the system pressure has dropped below approximately 1 bar, there may not be enough water in the circuit for adequate circulation. This is one of the few causes a homeowner can safely check and address by topping up via the filling loop.
- Faulty flow sensor or associated wiring Sometimes
Chaffoteaux boilers use flow sensors to confirm circulation is taking place. A sensor that has developed an open circuit or short circuit fault (similar to documented Chaffoteaux faults E08 and E11) can report a flow failure even if the pump itself is working correctly. Wiring damage or a loose connection can produce the same result.
- Water leak causing low water volume Sometimes
A slow leak from a seal, fitting, or heat exchanger joint can gradually reduce the amount of water in the system. This lowers pressure and can cause the pump to run dry or circulate poorly, both of which can trigger a flow check fault.
- PCB fault misreading circulation data Rare
In a small number of cases, the printed circuit board can incorrectly interpret signals from the pump or flow sensor, generating a spurious circulation fault. This is usually only suspected once the pump, sensors, and pipework have been ruled out.
How to fix it
- Check whether the display is showing 123 spontaneously or after menu navigation DIY safe
If the code appeared while you were pressing buttons on the boiler, you may have entered the installer configuration menu rather than triggered a fault. In that case, consult your boiler manual for how to exit without making changes. If the code appeared on its own during normal operation, proceed with the steps below as a circulation fault.
- Verify your gas supply is active DIY safe
Check that other gas appliances in your home — a hob or gas fire — are working normally. If there is no gas supply to the property, contact your gas supplier rather than resetting the boiler.
- Check the system pressure gauge DIY safe
The pressure gauge is usually visible through or on the front of the boiler casing. When the system is cold, pressure should read between 1.0 and 1.5 bar. If it reads below 1 bar, you can repressurise the system using the external filling loop — typically a braided hose with one or two valves located beneath the boiler. Open the valve(s) slowly, watch the gauge, and stop at around 1.2–1.3 bar. Close the valve(s) fully before attempting a reset.
- Attempt a single reset DIY safe
Press and hold the reset button (often marked with a flame and cross symbol) for approximately three seconds, then release and wait at least 60 seconds for the boiler to complete its start-up sequence. If the boiler fires up and runs normally, monitor it over the next day or two. If it locks out again with the same code, do not keep resetting — repeated resets can mask a worsening fault and may cause further damage.
- Check for any visible leaks around the boiler or pipework DIY safe
Look at the pipework immediately around the boiler for drips, damp patches, or mineral deposits that suggest a slow leak. Do not attempt to tighten fittings or disturb any components yourself — simply note the location and report it to your engineer.
- Contact a Gas Safe registered engineer to diagnose and repair the fault Gas Safe engineer
If the boiler continues to lock out after your safe checks, a Gas Safe registered engineer is required. They will inspect and test the circulation pump (checking for seizure, airlock, or electrical failure), assess the system for sludge or debris that may warrant a power flush, examine flow sensors and their wiring, check for leaks, and review the PCB if all other components test satisfactorily.
Parts you may need
- Circulation pump · from £120
- Flow sensor · from £35
- Flow sensor wiring harness · from £20
- Inhibitor and system filter (post power flush) · from £45
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£380, depending on the underlying cause.
Frequently asked questions
Is fault code 123 on a Chaffoteaux boiler always a circulation problem?
Not necessarily. On models with a structured two-digit display system (such as the Talia, Pigma, and Inoa ranges), 123 displayed during normal operation almost certainly indicates a flow check failure on the primary circuit. However, on some older or different Chaffoteaux models, 123 is an installer access code used to enter the advanced configuration menu — it is not a fault in that context. If you pressed buttons before the code appeared, check your manual. If it appeared on its own, treat it as a circulation fault and call an engineer if a reset does not resolve it.
Can I top up the pressure myself to fix code 123?
Yes, checking and topping up system pressure is a safe DIY task. If your pressure gauge reads below 1 bar, use the filling loop beneath the boiler to bring the pressure back up to around 1.2–1.3 bar when cold. This can resolve the fault if low pressure was the sole cause. However, if the pressure keeps dropping — meaning you need to repressurise more than once every few weeks — there is likely a leak somewhere in the system and a Gas Safe engineer should investigate.
How much does it cost to fix a Chaffoteaux circulation fault in the UK?
For most homeowners, the repair comes down to either a pump replacement or a power flush (or both). A circulation pump replacement typically costs £150–£350 all-in for parts and labour. A power flush to clear sludge from the system usually costs £300–£500 depending on the size of your system and your location. If the fault turns out to be a flow sensor, expect to pay roughly £100–£200 including labour. In rare cases where the PCB is at fault, a replacement board can cost £180–£400 for the part alone — if your Chaffoteaux boiler is over 10–12 years old and the PCB has failed, it is worth getting a boiler replacement quote alongside the repair quote.
My Chaffoteaux boiler keeps locking out with code 123 even after a reset — what should I do?
A single reset is a reasonable first step, but if the boiler locks out again with the same code, stop resetting it. Repeated resets will not fix an underlying fault and can in some cases mask a deteriorating component. The most common reason for repeated lockouts on this code is a circulation pump that is failing gradually, or a system heavily loaded with sludge restricting flow. Book a Gas Safe registered engineer who can carry out proper diagnostics — they may find a relatively straightforward pump or sensor fix, or identify that the system needs a power flush to restore adequate circulation.