ATAG 114 Fault Code: Causes, Fixes & Repair Costs
What does the ATAG 114 fault code mean?
Fault code 114 on an ATAG boiler indicates that the boiler's outdoor temperature sensor is not behaving as expected. The boiler cannot read a valid signal from the external sensor — this could be because the sensor is physically absent, its wiring has become disconnected or damaged, the sensor itself has failed, or a configuration parameter is set incorrectly. The outdoor sensor is used to help the boiler modulate heating output based on how cold it is outside (a feature known as weather compensation), so when this signal is lost or falls outside acceptable limits, the boiler logs fault 114. In many cases the boiler will continue to heat your home, but without the benefit of weather-compensated control.
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 at the boiler Common
The most frequent trigger for code 114 is a cable that has worked loose — or been inadvertently unplugged — at the boiler's terminal block. This is especially common after any recent work on the boiler or heating controls, such as a new smart thermostat installation (for example, a Tado or Nest), where the engineer or installer may have disturbed the outdoor sensor's wiring.
- Damaged or broken sensor cable Common
The cable running from the outdoor sensor to the boiler is typically routed through an external wall or along exposed pipework, leaving it vulnerable to physical damage, rodent interference, or degradation over time. A break anywhere along the cable will produce the same fault 114 reading. Cable continuity can be confirmed with a multimeter.
- Faulty or failed outdoor sensor Sometimes
Over time, the sensor itself can fail — either because moisture ingress has corroded its internals or because the thermistor element has drifted out of its valid resistance range. A sensor reading an implausible temperature (or none at all) will cause the boiler to flag code 114.
- Incorrect parameter configuration (Parameter 4.2.1) Sometimes
ATAG boilers use a parameter setting (4.2.1) to define the type of weather compensation or thermoregulation active on the system. If this parameter has been set to expect an outdoor sensor that is not actually fitted — or has been changed during a controls upgrade — the boiler will generate fault 114 even if the wiring is physically intact.
- Outdoor sensor not installed but expected by the system Rare
If the boiler's configuration has been set up for weather-compensated control but no outdoor sensor was ever physically fitted, the boiler will continuously report fault 114 because it is looking for a sensor that simply isn't there.
How to fix it
- Check the outdoor sensor wiring at the boiler terminal block DIY safe
Locate the boiler's terminal block — usually accessible by removing the boiler casing front panel. Look for the pair of wires connected to the outdoor sensor terminals. Ensure both wires are firmly seated, undamaged, and not corroded. Gently tug each wire to confirm it is properly secured. If you have recently had a smart thermostat or any other controls fitted, this wiring may have been disturbed during that work.
- Trace the sensor cable for visible damage DIY safe
Follow the outdoor sensor cable from the boiler terminal block to where it exits the property and out to the sensor location on the external wall. Look for any obvious signs of damage — cuts, crush marks, pinch points where the cable passes through a wall, or any area that looks chewed or corroded. Any damaged section of cable will need to be replaced by a competent person.
- Reset the boiler after checking connections DIY safe
Once you have inspected and re-seated any loose connections, perform a boiler reset using the reset button or procedure described in your ATAG user manual. Wait two to three minutes to see whether fault 114 clears. Do not reset the boiler more than two or three times in succession — repeated resetting without fixing the underlying issue will not help and may mask the fault.
- Check boiler parameter 4.2.1 (engineer or competent person task) Gas Safe engineer
If the wiring appears intact and the fault persists, the configuration parameter 4.2.1 on the boiler should be checked and adjusted to match whether or not an outdoor sensor is fitted and what type of thermoregulation is required. Accessing boiler parameters beyond the standard user menu requires engineer-level access and should be carried out by a competent heating engineer familiar with ATAG systems.
- Test sensor and cable continuity with a multimeter (engineer task) Gas Safe engineer
A heating engineer can use a multimeter to measure the resistance of the outdoor sensor (comparing it against the expected value at the ambient outdoor temperature) and to confirm cable continuity end-to-end. This will confirm whether the sensor, the cable, or the terminal connections are at fault, allowing the correct component to be replaced.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If checking and re-seating the wiring and performing a reset does not clear fault 114, the sensor or wiring harness will need to be tested and most likely replaced. Contact a Gas Safe registered engineer experienced with ATAG boilers. Although this particular fault is not gas-related, any work inside the boiler casing — including replacing sensors or adjusting engineer-level parameters — should be carried out by a suitably qualified professional. If your ATAG boiler is still under its warranty (up to 10 years, extendable to 14), contact ATAG directly on 0800 680 0100 before arranging your own repair, as the fault may be covered at no cost to you.
Parts you may need
- ATAG outdoor temperature sensor · from £35
- Sensor wiring harness / extension cable · from £25
- Terminal block connector set · from £12
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 £120–£280, depending on the underlying cause.
Frequently asked questions
Will my ATAG boiler still heat my home while fault code 114 is showing?
In most cases, yes. Fault code 114 relates to the outdoor temperature sensor used for weather compensation, not to the core heating or hot water function. The boiler will typically continue to operate but will revert to a fixed or manually set flow temperature rather than adjusting automatically based on external conditions. You may notice slightly less efficient heating until the fault is resolved.
Could fitting a new smart thermostat (such as a Tado or Nest) cause fault code 114?
Yes, this is a relatively common trigger. When a smart thermostat is installed, the engineer may inadvertently disturb the outdoor sensor's wiring at the boiler terminal block, or in some cases deliberately disconnect it if the new controls don't support weather compensation. If fault 114 appeared shortly after a thermostat installation, checking and reconnecting the outdoor sensor wiring should be your first step.
Is fault code 114 covered under the ATAG warranty?
ATAG boilers come with a standard 10-year warranty, which can be extended to 14 years when registered. If your boiler is within its warranty period and has been serviced annually as required, contact ATAG on 0800 680 0100 before arranging an independent repair — a faulty sensor or wiring fault may be covered at no cost to you. Note that missing an annual service can invalidate the warranty early.
How much does it cost to fix ATAG fault code 114 in the UK?
Because the outdoor sensor itself is a relatively inexpensive component (typically £25–£40 for the part), most homeowners can expect to pay in the region of £120–£280 all-in, covering call-out, labour, and any replacement parts. This assumes a straightforward sensor or wiring replacement. Costs at the higher end of the range typically reflect more extensive wiring damage requiring a full harness replacement. Prices in London and the South East are generally 20–35% higher than in other regions. If the PCB or another major component turns out to be the root cause, costs can rise significantly — a heating engineer will be able to advise after diagnosing the fault.