Alpha 0E25 Fault Code: Causes, Fixes & Repair Costs
What does the Alpha 0E25 fault code mean?
The Alpha 0E25 fault code (shown as plain E25 on many Alpha models) is commonly described as a 'dry fire' warning — the boiler attempted to fire but its flow sensor failed to detect adequate water circulating through the system. Without confirmed water flow, the boiler shuts down to protect the heat exchanger from damage. On certain Alpha models, particularly the E-Tec series, 0E25 can also indicate a PCB-level fault rather than a straightforward flow issue; on these models it groups alongside other PCB-related codes such as E21 and FE97. Because the two interpretations share the same code across the Alpha range, it is worth ruling out the simpler causes — low pressure, airlocks, a scaled heat exchanger — before assuming PCB failure.
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 system pressure has dropped below roughly 0.5 bar, the boiler cannot circulate water effectively and triggers the dry fire protection. This is often the first thing to check and the easiest to resolve yourself via the filling loop.
- Faulty or dirty flow sensor Common
The flow sensor (also called a flow switch or flow detector) tells the boiler whether water is actually moving. If the sensor is scaled up, damaged, or has failed electrically, it will report no flow even when the system pressure is normal, leading to a false dry fire fault.
- Airlock in the heating circuit Sometimes
Air trapped in the pipework or heat exchanger can interrupt water circulation. The boiler senses insufficient flow and locks out, even though the system is fully pressurised. Airlocks are common after draining work, new radiator installation, or a prolonged period of low pressure.
- Blocked or heavily scaled heat exchanger Sometimes
Limescale and sludge build-up inside the primary heat exchanger restricts the flow of water. The boiler detects inadequate circulation and triggers the dry fire code. This tends to occur in hard-water areas or in systems without a magnetic filter.
- PCB fault (0E25 prefix on E-Tec and similar models) Rare
On some Alpha E-Tec models the 0E25 display format specifically flags a PCB (printed circuit board) error rather than a flow-detection problem. In this case the board may be misreading sensor signals, or a component on the board itself has failed. This is a relatively uncommon root cause compared with pressure or flow sensor issues.
How to fix it
- Check the boiler's pressure gauge DIY safe
Look at the pressure gauge on the front of the boiler. For most Alpha boilers normal operating pressure is 1–1.5 bar when the system is cold. If the needle is below 0.8 bar, low pressure is likely causing the fault. Proceed to the next step to repressurise.
- Repressurise the system via the filling loop DIY safe
Locate the filling loop — usually a silver or grey braided hose with one or two valves beneath or near the boiler. Slowly open the valve(s) and watch the pressure gauge rise. Stop once the needle reaches around 1.2 bar, then close the valve(s) firmly. Never overfill beyond 1.5 bar on a cold system.
- Reset the boiler DIY safe
Once pressure is correct, press and hold the reset button (consult your Alpha manual for the exact location — it is typically a dedicated button or a mode-button combination). Allow the boiler to go through its ignition sequence. If the fault clears and the boiler fires normally, monitor the pressure over the next few days to check it is not dropping again. Repeat the reset no more than two or three times; persistent reappearance of the fault means a deeper issue is present.
- Bleed radiators to release any airlocks DIY safe
If pressure is fine but the fault persists, air in the system could be to blame. Using a radiator bleed key, open the bleed valve on each radiator (starting upstairs and working down) until water dribbles out steadily rather than sputtering air. Re-check and top up system pressure afterwards if it has dropped.
- Inspect and replace the flow sensor Gas Safe engineer
If the above steps do not clear the fault, the flow sensor is a strong suspect. A Gas Safe engineer will remove, inspect, and test the sensor and replace it if necessary. This is not a job for a homeowner as it involves draining part of the system and working inside the boiler casing.
- Flush or descale the heat exchanger Gas Safe engineer
Where limescale or sludge is restricting flow, a Gas Safe engineer can perform a power flush or chemical clean of the primary heat exchanger. This restores water circulation and removes the conditions that caused the dry fire fault. Adding a magnetic system filter at this point will help prevent recurrence.
- Have the PCB diagnosed and replaced if needed Gas Safe engineer
If the fault code displays as 0E25 and all flow-related causes have been ruled out, the PCB is likely at fault. A Gas Safe engineer (or specialist heating electrician working alongside one) will carry out diagnostics on the board. PCB replacement on Alpha boilers requires removal of the boiler casing, safe isolation, and correct programming of the new board — never attempt this yourself.
- Contact a Gas Safe registered engineer Gas Safe engineer
If any step above has not resolved the fault, or if you are unsure at any point, call a Gas Safe registered engineer. You can find one at the official Gas Safe Register website (gassaferegister.co.uk). If your Alpha boiler is still under warranty, contact Alpha directly first — sending an unauthorised engineer may invalidate your cover.
Parts you may need
- Alpha flow sensor / flow switch · from £35
- Alpha PCB (E-Tec series) · from £180
- Primary heat exchanger (Alpha E-Tec) · from £220
- Magnetic system filter (e.g. Magnaclean Pro2) · from £75
- Filling loop assembly · from £20
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–£380, depending on the underlying cause.
Frequently asked questions
What is the difference between the Alpha 0E25 and E25 fault codes?
They refer to the same underlying fault but are displayed differently depending on the model. Older and simpler Alpha models show just 'E25', while newer models such as the E-Tec series prefix it as '0E25'. The plain E25 is almost always a dry fire or flow-detection fault. The 0E25 format can indicate the same thing, but on certain E-Tec models it specifically points to a PCB-level fault. If you are unsure which interpretation applies to your boiler, check the model number in the installation manual or call Alpha technical support.
Can I fix the Alpha E25 fault myself?
There are a couple of safe checks you can carry out yourself: topping up system pressure via the filling loop and bleeding radiators to remove airlocks. These take only a few minutes and cost nothing. However, if the fault persists after those basic steps, the flow sensor, heat exchanger, or PCB is likely involved — all of which require a Gas Safe registered engineer to inspect and repair safely.
How much does it typically cost to repair an Alpha E25 fault in the UK?
For most households the repair falls between £100 and £380 including callout, labour, parts, and VAT. A flow sensor replacement is usually at the lower end of that range (around £100–£200), while a PCB replacement tends to sit between £250 and £380. Heat exchanger replacement is a larger job that can cost considerably more — often £450–£700 or beyond — but this is less common. If your boiler is more than ten years old and the repair estimate approaches or exceeds £400, it may be worth getting quotes for a new boiler installation instead.
Why does the Alpha E25 fault keep coming back after I reset it?
A fault that clears on reset but returns within hours or days usually means the underlying problem has not been resolved. If the boiler is losing pressure regularly, there is a leak somewhere in the system or the pressure relief valve is weeping — a Gas Safe engineer needs to find and fix the source. If pressure is consistently normal but the fault reappears, the flow sensor has probably degraded and needs replacing. Repeatedly resetting the boiler without fixing the root cause can cause overheating damage, so limit resets to two or three attempts before calling an engineer.