ATAG 102 Fault Code: Causes, Fixes & Repair Costs
What does the ATAG 102 fault code mean?
Fault code 102 on ATAG boilers signals that the boiler's control system has detected a problem with the water pressure sensor. This could mean the sensor itself has failed, that there is an issue with the wiring connected to it (such as a loose connection or an earth short), or that the system pressure has dropped to a level outside the sensor's expected operating range. Until the fault is resolved, the boiler will typically lock out to protect itself and the heating system from running under potentially unsafe conditions.
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
- Low system pressure Common
If the water pressure in your central heating system has dropped below the normal operating range (typically 1–1.5 bar on ATAG boilers), the pressure sensor will report an out-of-range reading and trigger code 102. This is the most straightforward cause and can be checked immediately on the boiler's pressure gauge.
- Failed or faulty pressure sensor Common
The pressure sensor itself can fail over time due to general wear, scale build-up, or internal damage. A sensor that has drifted out of calibration or stopped working entirely will send incorrect signals to the PCB, causing the boiler to fault even when system pressure is perfectly normal.
- Loose or corroded wiring connections Sometimes
The sensor connects to the PCB via a wiring loom. If a connector has worked loose, or if corrosion has built up on a terminal, the signal from the sensor can become intermittent or drop out entirely — producing a 102 fault that may appear and clear at random.
- Earth short in the sensor circuit Sometimes
A short to earth in the wiring harness between the pressure sensor and the PCB can mimic a sensor fault. This type of wiring fault requires specialist diagnostic equipment to identify and is not something a homeowner can safely investigate.
- PCB fault Rare
In rare cases, the fault lies not with the sensor or its wiring but with the PCB itself, which may be misreading or failing to process the sensor's signal correctly. PCB issues are uncommon relative to sensor or wiring faults but should be considered if no other cause can be found.
How to fix it
- Check the system pressure gauge DIY safe
Look at the pressure gauge on your ATAG boiler — it is usually visible through a window on the casing or on the display. The needle or reading should sit between 1 and 1.5 bar when the system is cold. If it is below 1 bar, low pressure may be triggering or contributing to the fault.
- Top up the system pressure using the filling loop DIY safe
If pressure is low, locate the filling loop (a braided or plastic hose with one or two valves, usually beneath the boiler). Open the valve(s) slowly and watch the gauge rise. Stop when the reading reaches approximately 1.2 bar, then close the valve(s) securely. Never exceed 1.5 bar. If you are unsure how to do this, consult your ATAG user manual or a short instructional video for your specific model.
- Reset the boiler DIY safe
Once pressure is at the correct level, press the reset button on the boiler's control panel and allow the boiler to run through its ignition sequence. Observe whether code 102 returns. Attempt a reset no more than two or three times in total — repeated resets without fixing the underlying problem will not help and may mask a developing fault.
- Check whether the fault recurs after resetting DIY safe
If the boiler fires up successfully and runs without the fault code returning, monitor it over the next few hours. If code 102 comes back, particularly when pressure is still within the correct range, this points strongly towards a sensor, wiring, or PCB issue rather than simply low pressure.
- Contact a Gas Safe registered engineer for sensor and wiring diagnosis Gas Safe engineer
If the fault persists or returns after a pressure top-up and reset, a Gas Safe registered engineer should inspect the pressure sensor and its associated wiring. The engineer will use diagnostic tools to test the sensor's output signal, check the wiring loom for continuity and shorts, and determine whether the sensor needs replacement or whether the fault lies further upstream in the circuit.
- Allow the engineer to replace the pressure sensor if required Gas Safe engineer
Replacing the pressure sensor involves depressurising the relevant part of the system, removing the old sensor, fitting a new one, and recommissioning the boiler. This must only be carried out by a Gas Safe registered engineer. The sensor itself is relatively inexpensive (typically £15–£35 for the part), and the job is usually completed within a single visit.
- Have the PCB inspected if no sensor or wiring fault is found Gas Safe engineer
If the engineer cannot identify a fault with the sensor or wiring, the PCB may be processing the sensor signal incorrectly. PCB diagnosis and replacement is specialist work and must be carried out by a Gas Safe registered engineer. Discuss repair versus replacement costs with your engineer, particularly if the boiler is older.
Parts you may need
- Water pressure sensor · from £25
- Sensor wiring loom / connector · from £20
- Filling loop assembly · from £18
- PCB (main circuit board) · from £290
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 £90–£280, depending on the underlying cause.
Frequently asked questions
Can I fix ATAG fault code 102 myself?
The safe DIY checks are limited to topping up the system pressure to 1–1.5 bar and pressing the reset button. If the code clears and stays away, you may not need an engineer at all. However, if it returns — especially when pressure is normal — the cause is almost certainly an internal component such as the pressure sensor, the wiring to it, or the PCB, and these require a Gas Safe registered engineer to diagnose and repair safely.
How much does it cost to fix ATAG fault code 102 in the UK?
For most people, the repair involves a pressure sensor replacement carried out by an engineer, which typically comes to between £90 and £280 including parts and labour. If the fault turns out to be a wiring issue, costs are usually at the lower end of that range. In the less common scenario where the PCB is at fault, the PCB part alone can cost £200–£400, making the total bill considerably higher — worth factoring in if your boiler is already approaching 10 years old.
Why does my ATAG boiler keep showing code 102 after I reset it?
A fault code that keeps returning after a reset (and once pressure has been checked and is correct) usually means the boiler's control system is repeatedly detecting the same problem — most likely a sensor that has genuinely failed or a wiring fault producing an intermittent signal. Resetting more than two or three times without fixing the root cause is not recommended, as it will not resolve the underlying issue and may eventually cause the boiler to lock out more firmly. Book a Gas Safe engineer to investigate.
Is ATAG fault code 102 dangerous?
Fault code 102 itself is a safety lockout — the boiler stops operating because it cannot confirm the system is at safe pressure. This is a protective response rather than an immediate danger. However, you should not attempt to bypass or ignore the fault, and you should not dismantle any part of the boiler. Low pressure left unchecked can cause long-term damage to the heat exchanger, and a faulty sensor means the boiler may not be able to detect genuine pressure problems in future.