Alpha boilers are considered an affordable, budget-friendly heating solution for UK households. While they may not carry the same reputation as premium brands like Worcester Bosch or Vaillant, Alpha models still receive positive feedback—currently rated 4.7 out of 5 on Trustpilot.
Even the most reliable boilers can experience a fault and lockout, then start flashing lights at you or displaying incomprehensible error codes. But don’t worry, you’ve come to the right place. This guide will help you identify the error code you’re seeing on your Alpha boiler and explain what the fault relates to.
It’s illegal to remove the cover on your Alpha boiler or attempt to fix an issue yourself unless you’re a qualified Gas Safe Engineer. You should always contact a certified engineer for any issue relating to your boiler or central heating system. This guide aims to help you diagnose the issue, so you can better understand the likely repair costs or decide whether replacing your Alpha boiler would be a better long-term solution.
If your boiler is still under warranty, your first step should be to contact Alpha. Provided you’ve met the warranty terms (such as getting your annual boiler service), they should be able to send an engineer to resolve the issue.
If your Alpha boiler is out of warranty and the cost to repair it seems high, it may be more cost-effective to consider a replacement. WarmZilla offers fixed-price boiler quotes starting from just £1,489, including installation, wireless controls, a system cleanse, a system filter, and a manufacturer-backed guarantee lasting between 5 and 10 years, depending on the boiler model you choose.
You can also spread the cost with boiler finance, with 0% interest available on selected models. Our lenders have a very high acceptance rate, even for those with less-than-perfect credit histories.
Hopefully, fixing the fault with your Alpha boiler won’t cost too much. But if the repair bill is around £400 and the boiler is already several years old, getting a new boiler installed could be more economical in the long run. WarmZilla makes that process simple, fast, and affordable.
Choose your Alpha boiler model or error type from the list below to diagnose an issue. We’ve grouped standard Alpha boiler fault codes by model and issue to help you identify the problem quickly and understand the next steps.
General Alpha Boiler Error/Fault Codes
Below is a table containing common Alpha boiler fault codes that apply to a range of Alpha boilers.
| Fault Code | Fault | Fault Description |
|---|---|---|
| 1 | Ignition failure | Gas supply, pressure tubes, ignition electrode, flame sensor electrode, ignition generator, lead flame sensor, electrode lead, gas valve setting, gas valve printed circuit board (PCB) |
| 2 | Overheat boiler lockout | Pump or flow problem, blocked heat exchanger, air in heat exchanger, overheat thermostat, thermal fuse (if open circuit then replace primary heat exchanger) |
| 3 | High flue thermostat temperature | Blocked or restricted primary flow, heat exchanger air flow blocked, flue restriction, flue sensor fault |
| 4 | Gas valve electrical connection fault | Gas valve lead connection fault, faulty gas valve or faulty printed circuit board (PCB) |
| 5 | Heating flow sensor fault | Flow sensor wire connections, flow sensor faulty |
| 6 | Domestic hot water (DHW) sensor fault | DHW sensor wiring connection or DHW sensor faulty |
| 8 | Maximum number of resets | Refer to fault history codes |
| 10 | Primary system pressure low | Check expansion vessel pressure (1 bar), leak in system, expansion relief valve operated or primary pressure switch |
| 12 | Cylinder sensor fault (FlowSmart only) | Cylinder sensor wiring connections or cylinder sensor faulty |
| 15 | Internal wiring error | Check internal wiring connections to printed circuit board (PCB), Combi boiler domestic hot water (DHW) sensor X4, System boiler link X14 |
| 16 | Fan fault | Fan wiring connections, fan fault or printed circuit board (PCB) fault |
| 20 | Flame sensing fault | Check flame sensing electrode and lead printed circuit board (PCB) fault |
| 24 | Control panel button fault | Jammed control panel or printed circuit board (PCB) buttons |
| 25 | Overheat lock out | Air in heat exchanger, blocked or restricted primary flow, heat exchanger air flow blocked, flue restriction, flue sensor fault, pump fault, boiler or heating circuit valve closed |
| 27 | Insufficient primary flow | Blocked or restricted primary flow, air in heat exchanger, boiler or heating circuit valve closed, pump fault or primary flow sensor fault |
| 29 | Flue sensor fault | Sensor wiring connection or flue sensor faulty |
| 31 | Loss of communication with external control (Alpha Climatic) | Remote control or receiver connection wiring |
| 37 | Low supply voltage | Check mains power supply |
| 38 | Loss of flame rectification | Flame sensing electrode and lead, check flue gas recirculation, check the gas valve settings and check the fan speed settings |
| 43 | Loss of flame rectification | Check gas supply working, check flame sensing electrode and lead, check for flue gas recirculation, check the gas valve settings, check the fan speed settings |
| 44 | Safety lock out | Check external control (room thermostat) requests and rapid on/off hot tap requests |
| 46 | External sensor intervention | External sensor and cable damaged or wet, continuity of external sensor and circuit, check connection at X19 on printed circuit board (PCB) and sensor connecting block |
| 47 | Reduced burner output | Air in heat exchanger, restricted primary flow, heat exchanger airflow blocked, flue restriction, flue sensor fault or pump fault |
| 51 | Climatic RF communication fault | Batteries need replacing, distance between boiler and climatic control too great, interference object blocking signal (metallic) |
Alpha E-Tec, E-Tec Plus, Evoke Combi Boiler Error/Fault Codes
Error codes relating specifically to the Alpha E-Tec, E-Tec Plus & Evoke combi boiler models.
| Fault Code | Fault | Fault Description |
|---|---|---|
| 60 | Pump error (stuck or there is an electrical pump fault) | Pump operation (may need to free the pump shaft), issue with pump wiring or pump replacement needed. |
| 61 | Air in the pump (restricted central heating flow) | Flow and Return valves may not be open, iIncorrect system pressure, system not purged properly or flow return valves are open. |
| 70 | Return/flow sensor Exchange from possible wiring fault | Issues with sensor wiring and connections. Issues with sensor resistance. |
| 75/76 | Return/flow sensor fault from possible failure of one or both sensors | Issues with sensor resistance. |
| SR | Service reminder | Service reminder countdown has reached 0 (this will not stop boiler from working) – boiler needs servicing. |
Alpha Protec Plus System Error Codes
Error codes relating to the Alpha Protec Plus System boiler.
| Fault Code | Fault | Fault Description |
|---|---|---|
| OA1 | Ignition failure | Issue with gas supply. Ignition electrode position and spark issues. |
| OA2 | Flame detection fault | Flame sensing electrode connections. A short circuit to the electrode or wires. |
| OA3 | Overheat thermostat lock-out | Flame sensing electrode connections. A short circuit to the electrode or wires. |
| OA5 | Fan speed fault | Problem with flue / ventilation. Issue with air inlet manifold and pipe. Damage or fault with fan. Fan wire connections. |
| OA7 | High flue temperature fault | Air in the primary heat exchanger. System restrictions causing overheating. Flue run may have restrictions or blockages. |
| OA8 | Flame circuit fault | Incorrect gas supply. Ignition electrode position and spark. Issues with flame sensing electrode gap and connections. |
| 0A9 | Gas valve electrical error | Valve connection issues. Main PCB. Gas valve operation issues. Gas contamination. |
| OA15 | Flow and return sensor anomaly detected. (incorrect temperature value shown on sensor.) | Poor or incorrect circulation. External circuit influences. Problem with resistances of flow and return sensors. |
| OA16 | Flow sensor temperature rise incorrect (time taken for flow temperature to rise is too long.) | System circulation issues. System volume or flow is too high. Boiler output is insufficient for the system. |
| OA17 | Return sensor temperature rise incorrect (time taken for flow temperature to rise is too long.) | System circulation issues. System volume or flow is too high. Boiler output is insufficient for the system. |
| OA18 | Flow and return sensor anomaly detected. Sudden temperature change detected on the flow or return sensor. | System circulation issues. Problem with operation of zone valves. Resistances and function of flow and return sensors needs checking. |
| OA21 | Main PCB fault | Electrical connections. Water ingress in connections. |
| OA30 | Flow sensor short circuit | Flow sensor connections and wires need checking. Water ingress in connections. |
| OA31 | Flow sensor out of range. (sensor measures a temperature not in normal range.) | Problem with flow sensor connections and damaged wires. Sensor resistance values wrong. |
| 0A37 – Pro Tec 50 | Insufficient system flow (if the system flow is too low for a certain length of time boiler will switch off) | Flow switch reading needs checking. Restrictions or shut valves in system. Pump function issues. System pressure issues. |
| OA43 | Return sensor short circuit | Problem with return sensor connections and wires. Water ingress in connections. |
| OA44 | Return sensor out of range. Sensor measures a temperature outside normal working range | Return sensor connections and damaged wires. Return sensor resistance values need checking. |
| OA80 | Flow and return sensor connection fault (may occur after several minutes of boiler operation.) | Wires are not connected to the correct sensors. |
| OE2 | Flame sensing fault. | Flame sensing electrode connections need checking. Short circuit to the electrode or wire. |
| OE13 | Maximum number of resets reached. (Over 5 reset attempts have been reached within 15 minutes.) | Investigate initial fault code displayed. Power supply needs to be turned Off/On to clear this code. |
| OE25 | Main PCB fault | All electrical connections need to be checked. Water ingress in connections. |
| OE33 | Low power supply voltage | Electrical socket connection issues. Problem with external power supply. Possible power disruptions. |
| OE34 | DHW sensor out of range (measures a temperature outside normal working range.) | DHW sensor connections and damaged cables. Issues with DHW sensor resistance values. |
| OE37 | Insufficient system pressure | System needs checking for circulation and restrictions. System pressure and gauge needs checking. Pressure switch and connections need checking. |
| OE45 | Flue sensor short circuit | Flue sensor connections and wires need checking. Water ingress in connections. |
| OE46 | Flue sensor out of range (measures a temperature outside of normal working range) | Flue sensor connections, wires and flue sensor resistance values need checking. |
| OE81 | Flow and return sensor anomaly detected (the sensor shows an incorrect temperature value) | Poor or incorrect circulation / external circuit influences resistance of flow return sensors need checking. |
| OE98 | Flow and return sensor anomaly detected (sensor shows incorrect temperature value) | M to O Connections need checking. Compatible software on PCB needs checking. |
| OE99 | Simple cascade communication error | Wiring connections needs checking on all boilers. Configuration, parameter 38. |
| FE94 | Display PCB fault. | Electrical connections to display board need checking. Water ingress in connections. Damage to buttons or LCD screen. |
| FE95 | External flow sensor out of range or short circuit. External flow sensor measures a temperature outside normal working range. | External flow sensor connections and wires need checking for damage. External flow sensor resistance values need checking to make sure they are between 5 and 0. |
| FE96 | External sensor fault | External sensor connections and wires need checking. Water ingress in connections. Boiler parameter settings are incorrect. |
| FE97 | Boiler PCB configuration error (may occur if the main PCB or display PCB is changed.) | All electrical connections. Incorrect parameter settings on PCB. Press ‘–‘ CH button until ‘AUTO’ appears, then press and hold ‘RESET’ button until ‘bu1’ appears. |
Alpha Flashing Light Error Codes
All Alpha boiler errors communicated by flashing lights.
| Light Sequence | Fault | Fault Description |
|---|---|---|
| No lights on | Electricity fault | Check your electricity supply |
| Illuminated red A or B | Burner has failed to light | Rotate selector switch to the reset position (3) and the ignition sequence will restart after a delay of about 30 seconds |
| Illuminated yellow B or C | Burner is alight | No action required |
| Flashing yellow every 5 seconds or illuminated green D | Electrical supply to the boiler is on | No action required |
| Flashing yellow B or flashing red A | Temperature sensor fault | Contact a Gas Safe engineer |
| Illuminated red A and flashing yellow B or flashing red A and flashing red B | Blocked flue or fan fault | Contact a Gas Safe engineer |
| Flashing yellow or flashing red A or flashing (alternating) red A and flashing (alternating) yellow B | System pressure is very low and re-pressurisation is required | Contact a Gas Safe engineer |
| Illuminated red A and flashing yellow B | Pump fault or restricted flow | Contact a Gas Safe engineer |
| Flashing red A and flashing red B and flashing yellow C | Temperature sensor wiring or flow and return connections incorrect | Contact a Gas Safe engineer |
| Flashing red A and flashing red B and flashing yellow C indicators | Flue temperature too high (air in the heat exchanger, heat exchanger blocked) | Contact a Gas Safe engineer |
Alpha E-TEC Regular Gas Boiler Error Codes
All Alpha E-Tec Regular boiler codes are located in the table below.
| Fault Code | Fault | Fault Description |
|---|---|---|
| 1 | Ignition failure | Check the gas supply, pressure tubes, ignition electrode, flame sensor electrode, ignition generator or lead flame sensor, gas valve setting and PCB. |
| 2 | Overheat boiler lockout | Pump or flow problem. Caused by a blocked heat exchanger, air in heat exchanger, overheated thermostat, thermal fuse (if open circuit then replace primary heat exchanger). |
| 3 | High flue thermostat temperature | Blocked or restricted primary flow. Heat exchanger air flow blocked, flue restriction, flue sensor fault. |
| 4 | Gas valve electrical connection fault | Gas valve lead connection fault. Faulty gas valve or faulty PCB. |
| 5 | Heating flow sensor fault | Flow sensor wire connections. Flow sensor faulty. |
| 6 | Internal wiring error | Incorrect wiring configuration detected. Internal wiring connections to PCB need checking. |
| 7 | Chimney sweep function is active | Chimney sweep function is active. E07 is displayed on the climatic remote control. |
| 8 | Maximum number of resets | Refer to fault history codes. |
| 12 | Cylinder sensor fault (FlowSmart only) | Cylinder sensor wiring connection – cylinder sensor faulty. |
| 16 | Fan fault | Check fan wiring connection, fan fault or PCB fault. |
| 20 | Flame sensing fault | Check flame sensing electrode and lead PCB for faults. |
| 23 | Heating return sensor fault | Incorrect return sensor resistance value – return sensor wire connections or sensor could be faulty. |
| 24 | Control panel button fault | Control panel button is stuck in the ‘on’ position – check for jammed control panel buttons or jammed PCB button. |
| 27 | Insufficient primary flow | Blocked or restricted primary flow. Air in heat exchanger, boiler or heating circuit valve closed, pump fault or primary flow sensor fault. |
| 29 | Flue sensor fault | Check sensor wiring connection – flue sensor faulty. |
| 31 | Loss of communication with external control (Alpha Climatic) | Remote control or receiver connection wiring. |
| 37 | Low supply voltage | Check mains power supply. |
| 38 | Loss of flame rectification | Check flame sensing electrode and lead and for flue gas recirculation. Check or adjust the gas valve settings. Check or adjust the fan speed settings. |
| 43 | Loss of flame rectification | Check gas supply/working pressure, flame sensing electrode and lead, check for flue gas recirculation, check/adjust the gas valve settings, check/adjust the fan speed settings. |
| 44 | Safety lockout | Check external control (room thermostat) requests. Rapid on/off hot tap requests. |
| 45 | High-temperature difference | The boiler is detecting an unexpected increase between the system flow and return sensors. Boiler output is limited for boiler protection and once restored the boiler resumes regular operation. |
| 46 | Optional thermostat intervention | No continuity of optional thermostat circuit – check the optional thermostat and cable are not damaged or wet. |
| 47 | Reduced burner output | Flue thermostat has sensed high flue gas temperature and reduced the burner output to prevent damage. If the temperature continues to rise the boiler will lockout and the E03 error code will be displayed. This could be due to air in the heat exchanger, restricted primary flow or heat exchanger air blocked. |
| 49 | Return sensor high temperature intervention | Return sensor has detected a high temperature on the exchanger return circuit. |
| 51 | Climatic RF communication fault | The error between the communication of the climatic transmitter and boiler receiver. Could mean the batteries need replacing or the distance between the boiler and climatic control is too great or a metal object is blocking the signal. |
| 70 | Return flow sensor error | Possible wiring faults sensor is incorrectly fitted or the system is blocked – check the sensor wiring and connections, also check sensor resistance and circulation. |
| 71 | No primary temperature increase detected | From ignition the boiler detects no temperature rise in the primary circuit – check system filling and venting, airlocks preventing flow check, blocked flow, or closed valves. |
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