Ariston 102 Fault Code: Causes, Fixes & Repair Costs
What does the Ariston 102 fault code mean?
Fault code 102 on Ariston boilers signals that the heating circuit pressure sensor has detected either an open circuit or a short circuit condition. In plain terms, the boiler's control board is receiving an abnormal signal from the sensor that monitors your central heating system pressure — either no signal at all, or a voltage reading that falls outside the expected range (typically 0 V or 5 V when it should be somewhere in between). Because the boiler can no longer trust the pressure reading, it locks out to prevent any risk of running dry or over-pressurising the system. The fault could mean the sensor itself has failed, or it could point to a wiring issue feeding it — but very low actual system pressure is worth ruling out first before any component is condemned.
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
- Very low system pressure Common
If the system pressure has dropped below roughly 0.5 bar, the sensor may produce a signal the PCB interprets as a fault rather than a valid low-pressure reading. Check the pressure gauge on the boiler fascia — if the needle is in the red or below 1 bar, this is the most likely starting point.
- Failed pressure sensor Common
The sensor itself may have developed an internal open or short circuit, producing an out-of-range voltage regardless of actual system pressure. This is confirmed when the pressure gauge reads normally (around 1–1.5 bar) but the fault code persists after a reset.
- Damaged or corroded wiring and connectors Sometimes
The wiring loom running between the pressure sensor and the PCB can suffer from loose terminals, corrosion, or physical damage — especially in older boilers or where condensation is present. A poor connection can mimic a failed sensor exactly.
- Faulty PCB Rare
If the sensor and its wiring both test correctly, the fault may lie with the PCB itself failing to process the sensor signal accurately. This is comparatively rare and is usually only confirmed after the other causes have been eliminated by an engineer.
How to fix it
- Check the system pressure gauge DIY safe
Look at the pressure gauge on the front of your boiler. For most Ariston models it should sit between 1.0 and 1.5 bar when the system is cold. If it reads below 1 bar — or the needle is in the red — low pressure is likely contributing to the fault and topping up should be your first action.
- Top up system pressure using the filling loop DIY safe
Locate the filling loop — usually a silver braided hose with one or two valves beneath the boiler. With the boiler off, open the valve(s) slowly and watch the pressure gauge rise. Stop when the needle reaches approximately 1.2–1.5 bar, then close the valve(s) fully. Never overfill beyond 2 bar. If you cannot locate the filling loop or are unsure, refer to your boiler's user guide or call an engineer.
- Reset the boiler DIY safe
Once pressure is correct, press and hold the reset button (usually marked with a flame or 'R' symbol) for around 5 seconds until the boiler attempts to restart. If the fault code clears and the boiler runs normally, monitor the pressure over the next few days. If code 102 returns straight away or after one or two heating cycles, do not keep resetting — move to the next step.
- Have a Gas Safe engineer test the pressure sensor and wiring Gas Safe engineer
An engineer will measure the voltage signal at the sensor terminals and compare it against the expected range. If the wiring is sound but the sensor voltage is reading 0 V or 5 V (the fault thresholds), the sensor will be replaced. Ariston pressure sensors are a relatively straightforward component swap, and this resolves the majority of persistent 102 faults.
- Have a Gas Safe engineer inspect or replace the PCB if required Gas Safe engineer
If a new sensor and verified wiring still fail to clear the fault, the engineer will assess the PCB. A PCB replacement is a more involved repair and carries a higher cost — see the FAQ below for guidance on whether repair or full boiler replacement makes more sense at that point.
Parts you may need
- Heating circuit pressure sensor · from £35
- Sensor wiring harness / connector · from £20
- Printed circuit board (PCB) · from £220
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
Can I fix Ariston fault code 102 myself?
Partially. You can safely check and top up the system pressure to 1.0–1.5 bar using the filling loop, then attempt a reset. If that clears the fault, you may not need an engineer at all. However, if the code returns, the sensor or wiring needs professional diagnosis — that work must be done by a Gas Safe registered engineer, not a homeowner.
How much does it cost to fix a fault code 102 on an Ariston boiler in the UK?
Most people pay between £100 and £280 for a fault code 102 repair. This typically covers the engineer's call-out and labour plus the cost of a replacement pressure sensor if needed. If the PCB turns out to be the culprit, parts alone can reach £200–£250 on top of labour, pushing the total closer to £400–£500. At that level it is worth getting a boiler replacement quote alongside the repair quote, particularly if your boiler is over 10 years old.
Why does my Ariston boiler keep losing pressure and showing code 102?
A boiler that repeatedly drops pressure usually has a slow leak somewhere in the system — this could be a radiator valve, a pipe joint, the pressure relief valve discharging, or even the filling loop valve not sealing fully. A Gas Safe engineer can carry out a system leak check. Recurring low pressure is not something that should be fixed by simply topping up repeatedly, as it can eventually cause corrosion and sludge build-up inside the heat exchanger.
Is fault code 102 dangerous?
The fault itself is not a gas leak or carbon monoxide risk — it is an electrical signal fault on the pressure sensor circuit. The boiler locks out as a precaution to protect the heat exchanger from running at incorrect pressure. It is safe to be in your home with this fault showing, but the boiler will not provide heating or hot water until the fault is resolved. Do not attempt to bypass or ignore the lockout.