Ariston 307 Fault Code: Causes, Fixes & Repair Costs
What does the Ariston 307 fault code mean?
Fault code 307 on an Ariston boiler signals an internal fault with the electronic control board (ECB), also known as the printed circuit board or PCB. This is the component that manages every function of your boiler — from ignition sequencing to temperature regulation — so when it develops a problem, the boiler will typically lock out completely or behave erratically. Codes in the 301–307 range all relate to PCB-level issues, but 307 (along with 303, 305, and 306) is considered one of the more serious entries in this group, frequently pointing to board damage or failure rather than a minor communication glitch. If this code appears on your display, a Gas Safe registered engineer will need to diagnose the board before the boiler can be safely returned to service.
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
- PCB component failure or end-of-life degradation Common
After years of daily cycling, individual components on the board — capacitors, relays, and processor circuits — can degrade or fail outright. This is the most common reason for a 307 on boilers that are more than eight to ten years old, and it typically means the board needs replacing rather than repairing.
- Moisture or condensation ingress Common
Boilers installed in lofts, garages, or utility rooms are exposed to temperature swings that can cause condensation to form inside the casing. Over time, moisture tracks across the board, causes corrosion on connectors, and can short circuit sensitive components. UK damp conditions make this a particularly frequent culprit.
- Electrical surge or supply voltage irregularity Sometimes
A power surge — from a grid spike, a nearby lightning strike, or a poor mains supply — can damage or destroy the logic circuits on the PCB in an instant. Repeated low-voltage brownouts are almost as harmful, gradually stressing components until one fails.
- Loose or corroded wiring connections to the board Sometimes
Vibration over time can work connector plugs loose from their sockets on the PCB. Corroded terminals can also increase resistance and cause erratic signals. Occasionally this is all that is wrong, making it a relatively straightforward fix once an engineer traces the fault.
- Earthing or polarity fault in the mains supply Rare
A poor earth connection to the boiler, or reversed live and neutral wiring at the spur, can produce stray voltages that upset the board's reference signals. This is less common but worth ruling out when 307 appears on a recently installed boiler or after electrical work in the property.
How to fix it
- Switch the boiler off at the mains and leave it for five minutes DIY safe
A full power-down — not just a panel reset — allows any residual charge to clear. After five minutes, restore power and observe whether the boiler starts normally or the 307 code returns. If it starts cleanly, monitor over the next few heating cycles; if the code comes back, move on.
- Attempt a boiler reset (no more than two or three times) DIY safe
Use the reset button or procedure described in your Ariston user manual. Pressing reset on a 307 code occasionally clears a one-off communication glitch, but if the fault returns within a short time, repeated resetting will not resolve the underlying issue and could mask a developing problem.
- Check that your mains electrical supply is healthy DIY safe
Confirm that other appliances on the same circuit are working normally and that no fuses or circuit breakers have tripped. If you suspect recent surge damage or your supply is known to be unstable, mention this to the engineer — it may point to an earthing or supply issue rather than a failed board.
- Do not attempt to open the boiler casing or inspect the PCB yourself Gas Safe engineer
The PCB sits inside a pressurised gas appliance and is surrounded by live electrical terminals, gas-carrying components, and high-voltage connections. Removing casing panels and probing internal circuits requires specialist diagnostic equipment and Gas Safe registration. Any DIY interference risks electric shock, gas escape, or voiding your boiler warranty and home insurance.
- Contact a Gas Safe registered engineer to diagnose the board Gas Safe engineer
An engineer will use a calibrated multimeter to test voltage rails, check connector integrity, and confirm whether the fault lies in the PCB itself, in a wiring harness, or in the mains supply. They will check earthing and polarity at the boiler spur before condemning the board, since a wiring fix is significantly cheaper than a replacement PCB.
- Have the engineer assess whether repair or replacement is the right course of action Gas Safe engineer
If the PCB is confirmed faulty, the engineer should advise you on the cost of a replacement board versus the age and overall condition of the boiler. On boilers over ten years old, a new PCB can cost nearly as much as a significant fraction of a replacement boiler, so getting a new-boiler quote alongside the repair estimate is sensible.
Parts you may need
- Ariston replacement PCB / electronic control board · from £280
- Wiring harness and connector loom · from £55
- Boiler surge protection device (mains spur filter) · from £35
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–£450, depending on the underlying cause.
Frequently asked questions
Can I reset an Ariston 307 fault myself and will it fix it?
You can try a full power-down reset — switching off at the mains for five minutes — and use the panel reset button once or twice. Occasionally a one-off electrical glitch will clear this way. However, fault 307 is one of the more serious codes in the 301–307 range and frequently indicates genuine PCB damage. If the code returns after resetting, a Gas Safe engineer needs to investigate; repeated resets will not resolve a hardware fault.
How much does it cost to replace an Ariston PCB in the UK?
A Gas Safe engineer call-out and PCB replacement on an Ariston boiler typically costs between £150 and £450 including parts and labour, depending on the specific model and how accessible the board is. The board itself can range from roughly £150 to £300 depending on the Ariston model. On older or discontinued models, sourcing the board can push costs higher — occasionally above £500 — which is why engineers will often advise getting a new-boiler quote at the same time for any boiler that is more than ten years old.
What is the difference between Ariston fault codes 301, 303, 305, 306, and 307?
All codes from 301 to 307 point to problems with the electronic control board rather than with external components like the pump or sensors. Codes 301 and 302 tend to indicate communication or EEPROM read errors that can sometimes be cleared by a reset. Codes 303, 305, 306, and 307 are generally regarded as the more serious end of the range, typically indicating component-level failure on the board itself rather than a recoverable software error. In practice, if your display shows 305, 306, or 307, you should expect the engineer's findings to lean towards board replacement.
Is it worth repairing an Ariston boiler showing fault 307, or should I buy a new one?
It depends mainly on the boiler's age and general condition. If the boiler is under eight years old and otherwise well maintained, replacing the PCB is usually worthwhile. If the boiler is over ten to twelve years old, has a history of faults, or the repair quote exceeds roughly 40–50% of the cost of a new equivalent model, most heating engineers and consumer guidance suggests getting new-boiler quotes. A new A-rated condensing boiler will also reduce gas bills compared with an ageing, less efficient model — worth factoring in alongside the repair cost.