Alpha 0A7 Fault Code: Causes, Fixes & Repair Costs
What does the Alpha 0A7 fault code mean?
The 0A7 code belongs to Alpha's 0A series of resettable anomaly codes and indicates that the flue temperature sensor has detected exhaust gases leaving the boiler at an abnormally high temperature. When this threshold is exceeded, the boiler locks out as a safety precaution to prevent damage to the flue system or a potential fire risk. After shutdown, the boiler runs a short post-ventilation cycle of around 60 seconds before it can be reset. If the underlying cause is not addressed, the fault will return promptly after each reset attempt.
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
- Blocked or restricted flue terminal Common
Debris, bird nesting material, ice, or physical damage at the external flue terminal can obstruct the flow of combustion gases. This traps heat inside the flue run and rapidly pushes temperatures above the safe operating limit, triggering the 0A7 lockout.
- Fan failure or weak fan performance Common
The flue fan is responsible for drawing combustion gases through the heat exchanger and out of the flue. If the fan motor is deteriorating, its impeller is damaged, or wiring connections to the fan are loose, airflow drops and heat builds up in the flue. Engineers should check both fan operation and its electrical connections.
- Faulty flue temperature sensor Sometimes
The sensor itself may have drifted out of calibration or developed an internal fault, causing it to report a high-temperature reading even when actual flue conditions are normal. This produces a false lockout that recurs regardless of flue condition.
- Airlock in the primary heat exchanger Sometimes
Air trapped within the heat exchanger disrupts water flow through it, reducing the boiler's ability to transfer heat into the system. This causes localised overheating that can elevate flue gas temperatures above normal levels.
- Poor system circulation or internal blockage Sometimes
Sludge deposits, a failing pump, or a partially closed valve can restrict water flow around the system. Reduced circulation means the heat exchanger cannot shed heat efficiently, and exhaust temperatures rise as a result.
How to fix it
- Allow the post-ventilation cycle to complete DIY safe
After the boiler locks out with 0A7, leave it alone for at least 60–90 seconds. Alpha boilers run a brief cooling fan cycle before they are ready to reset. Interrupting this early can mask whether the reset has taken effect.
- Visually inspect the external flue terminal DIY safe
Go outside and look at the point where the flue exits the building. Check for obvious obstructions such as leaves, a bird nest, ice build-up in cold weather, or physical damage to the terminal cover. Do not reach into the flue or remove any internal components — this is a visual check only.
- Attempt a single boiler reset DIY safe
Using the reset button or selector switch as described in your boiler's user guide, attempt one reset. Watch whether the boiler fires normally and runs through a full heating cycle without the 0A7 code returning. Limit yourself to no more than two or three reset attempts in total; repeated resetting without fixing the cause can mask a worsening fault.
- Check system pressure is within range DIY safe
Look at the pressure gauge on the boiler. It should read between 1 and 1.5 bar when the system is cold. If pressure is below 1 bar, top up via the filling loop following the instructions in your user manual. Low pressure alone is unlikely to cause 0A7, but it rules out a contributing circulation issue.
- Call a Gas Safe registered engineer if the fault returns Gas Safe engineer
If 0A7 reappears after resetting, do not keep resetting the boiler. A Gas Safe engineer needs to attend to measure flue gas temperatures directly, inspect the fan and its wiring, test the flue temperature sensor with appropriate equipment, check the heat exchanger for airlocks, and assess overall system circulation. Working inside the boiler casing or on any gas-carrying component is illegal for anyone who is not Gas Safe registered.
- Engineer to inspect and clear the flue run Gas Safe engineer
The engineer will check the full flue route including the air inlet manifold and connecting pipework for restrictions, damage, or incorrect installation. Any blockages will be cleared and the terminal condition assessed.
- Engineer to test the fan and replace if necessary Gas Safe engineer
Fan speed and electrical continuity will be tested. A fan that is running below specification will be replaced. Connections and wiring harnesses will also be inspected for corrosion or damage.
- Engineer to test or replace the flue temperature sensor Gas Safe engineer
The sensor resistance will be checked against the expected value at a known temperature. A sensor that reads outside tolerance will be replaced with a genuine Alpha-compatible part.
Parts you may need
- Flue temperature sensor · from £35
- Boiler flue fan (combustion fan assembly) · from £90
- Flue terminal and exhaust cowl · from £40
- System circulating pump · from £75
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–£380, depending on the underlying cause.
Frequently asked questions
Can I reset an Alpha 0A7 fault myself?
Yes, a single reset is safe to attempt once the 60-second post-ventilation cycle has finished. However, if the 0A7 code comes back after one or two resets, stop resetting and call a Gas Safe engineer. Repeated resets without fixing the cause will not clear the fault and may mask a worsening problem.
Is a high flue temperature fault dangerous?
The boiler has locked itself out precisely to prevent danger, so as long as you leave it off and do not attempt to bypass the lockout, you are not at immediate risk. However, the underlying cause — whether a blocked flue, failing fan, or overheating heat exchanger — does need professional attention before you run the boiler again.
How much does it cost to fix an Alpha 0A7 fault?
Most repairs for this fault fall in the range of £120 to £380 including call-out, labour, and parts. A straightforward flue clearance or sensor swap sits at the lower end; fan replacement with labour typically lands in the middle. Complex flue replacement work (particularly vertical or extended flue runs) can cost £400–£700 or more, but this is less common — if your engineer quotes for a full flue replacement, ask for a breakdown of exactly what needs changing and why.
Why does 0A7 keep coming back after I reset it?
If the fault returns within minutes or during the next heating cycle, the root cause has not been resolved. Common culprits are a fan that is still operating below spec, a flue obstruction that was not fully cleared, or a temperature sensor that has failed and is giving a permanently high reading. An engineer needs to carry out proper diagnostics rather than relying on further resets.