ATAG 10 Fault Code: Causes, Fixes & Repair Costs
What does the ATAG 10 fault code mean?
Fault code 10 on ATAG boilers signals a problem with the outdoor temperature sensor. The boiler expects to read a valid signal from this sensor — used for weather compensation to fine-tune heating output based on external conditions — but is either receiving no signal, an out-of-range value, or detecting a short circuit. This is a blocking-type fault rather than a full lockout, meaning the boiler may continue to operate in a limited capacity and can clear itself if the underlying problem resolves. However, repeated occurrences will eventually lock the boiler out entirely. Note: on later-generation ATAG i Series models the same fault is logged as code 114 — the cause and fix are identical regardless of which number appears on your display.
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
- Outdoor sensor wiring disconnected or damaged Common
The most frequent trigger. The cable running from the outdoor sensor to the boiler may have worked loose at either end, been cut, or developed a break or corroded connection along its length. The boiler sees no valid signal and raises the fault.
- Faulty outdoor sensor Common
The sensor unit itself may have failed — either due to age, water ingress, or physical damage — and is producing readings outside the acceptable range, or no reading at all.
- Lost Wi-Fi or internet connection (ATAG One users) Sometimes
If your system uses the ATAG One smart control with internet-based weather data rather than a physical sensor, a dropped Wi-Fi connection or loss of internet access will prevent the weather feed from reaching the boiler and trigger this code.
- Weather compensation configured but no sensor present Sometimes
If the boiler's settings expect an outdoor sensor or internet weather feed but neither is connected or active, it will continuously flag this fault. This can happen after a factory reset or if the boiler was set up incorrectly during installation.
How to fix it
- Check whether you use internet weather or a physical outdoor sensor DIY safe
Look at your ATAG One thermostat or control app settings, or check whether a small sensor box is mounted on an outside wall connected by cable to the boiler. Knowing which setup you have determines the correct next step.
- ATAG One users: check your Wi-Fi connection DIY safe
On your router or phone, confirm your home Wi-Fi is working and that the ATAG One controller is connected to it. Restart your router if needed. Once internet access is restored the boiler should clear the fault on its own within a few minutes.
- Physical sensor users: inspect the sensor wiring at both ends DIY safe
Trace the sensor cable from the outdoor unit back to the boiler. Check that the cable is firmly plugged into the correct terminals on the boiler's connection block and has not pulled loose. Look along the cable run for any obvious damage such as cuts, pinching, or weathering. Do not touch any gas or internal boiler components — limit your inspection to the low-voltage sensor cable only.
- Reset the boiler once DIY safe
Press and hold the reset button on the boiler control panel as described in your user manual. Allow the boiler to complete its start-up sequence and observe whether the fault returns. A single reset is reasonable; if the code comes straight back, do not keep resetting — it will not resolve the underlying issue.
- Contact a Gas Safe registered engineer for further diagnosis Gas Safe engineer
If the fault persists after the checks above, an engineer will use a multimeter to test sensor continuity, check wiring integrity from the PCB terminals outward, and confirm whether the sensor or wiring harness needs replacing. If the boiler has been configured to look for a sensor that was never installed, the engineer can adjust the weather compensation settings accordingly. Check your ATAG warranty (up to 10–14 years on some models) before paying — the repair may be covered.
Parts you may need
- ATAG outdoor temperature sensor · from £35
- Outdoor sensor wiring harness / extension cable · from £20
- ATAG One smart control unit (if replacing due to connectivity fault) · from £180
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 £100–£280, depending on the underlying cause.
Frequently asked questions
Is fault code 10 the same as fault code 114 on ATAG boilers?
Yes, effectively. ATAG revised their fault-code numbering between boiler generations. First-generation i Series models display this outdoor sensor fault as code 10, while later models show code 114. The underlying cause — a missing, disconnected, or faulty outdoor sensor — and the diagnostic steps are identical for both codes.
My boiler is still producing hot water — do I need to fix this urgently?
Because code 10 is a blocking fault rather than a full lockout, your boiler may carry on running in a reduced mode without weather compensation. However, this is not something to ignore long-term. Repeated blocking events will eventually cause the boiler to lock out completely, and running without weather compensation is less efficient, meaning higher energy bills. Aim to get it looked at within a week or two.
Can I just disable the outdoor sensor to clear the fault?
In principle, the weather compensation function can be switched off or reconfigured so the boiler no longer expects a sensor reading. A Gas Safe engineer can make this change in the boiler's service menu. This is a legitimate option if you no longer want to use weather compensation, but it should be set correctly by a professional — guessing at menu settings risks introducing new problems.
How much does it cost to replace an ATAG outdoor sensor in the UK?
For most people, an outdoor sensor replacement comes to £100–£280 all-in once you factor in the part (typically £30–£50) and the engineer's labour and call-out fee. Simple wiring repairs at the cheaper end, or a full sensor swap at the higher end. In the rare situation where wiring damage has affected the PCB's sensor circuit, PCB replacement can push costs to £300–£500 — but this is uncommon and worth checking warranty cover for first.