Vokera AL41 Fault Code: Causes, Fixes & Repair Costs
What does the Vokera AL41 fault code mean?
The AL41 code (also shown simply as A41 on many Vokera displays — both refer to the same fault) is a transitional low-pressure warning. It triggers when the system water pressure drops below 0.3 bar, which the boiler considers unsafe for continued operation. Vokera gives the boiler a 10-minute window to allow you to act; if the pressure is still too low after that period, the code upgrades to A40, which is a full lockout. Think of A41 as an early alert — the boiler is telling you the system needs water before it shuts down completely. In rare cases, a faulty pressure sensor can also cause A41 to appear even when actual system pressure is normal, because the boiler cannot read the pressure correctly.
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
- System pressure has dropped naturally over time Common
Sealed central heating systems gradually lose small amounts of water through micro-leaks at joints, radiator valves, and pump seals. Over months or years this can bring pressure below the 0.3 bar threshold that triggers A41. This is the most common reason for a first-time A41 on an older system.
- Radiators were recently bled Common
Bleeding radiators releases trapped air but also a small amount of water, which reduces system pressure. If you or an engineer recently bled the radiators and pressure wasn't topped back up afterwards, A41 will appear shortly after.
- Leak in the system or boiler Sometimes
A dripping pipe joint, corroded radiator, weeping pump seal, or internal boiler leak causes a more rapid and persistent pressure drop. If the pressure falls again within days of topping up, a leak is the likely culprit and needs to be traced and repaired by an engineer.
- Faulty or waterlogged expansion vessel Sometimes
The expansion vessel absorbs pressure changes as water heats and cools. If its internal diaphragm fails or the pre-charge pressure drops, the system pressure fluctuates erratically or falls repeatedly. Re-pressurising may give only temporary relief before A41 returns.
- Faulty pressure sensor Rare
A defective pressure sensor may report a falsely low pressure reading to the boiler's PCB, triggering A41 even when the actual system pressure is within range. This is less common but worth considering if pressure appears normal on the gauge yet the fault persists after a top-up.
How to fix it
- Check the pressure gauge DIY safe
Locate the pressure gauge on your Vokera boiler — it is usually a dial or digital readout on the front panel. A cold system should read between 1.0 and 1.5 bar. If it is sitting at or below 0.3 bar, the A41 code is directly caused by low pressure and you can top it up yourself.
- Top up system pressure using the filling loop DIY safe
Find the filling loop — a short braided hose with one or two valves connecting the cold mains supply to the heating system, often beneath the boiler. Slowly open the valve(s) and watch the gauge rise. Stop when it reaches 1.2–1.5 bar, then close the valve(s) firmly. Do not overfill; above 2.0 bar the pressure relief valve may discharge. If your boiler has an external filling key rather than a loop, use that as described in your Vokera user guide.
- Reset the boiler DIY safe
Once pressure is back in range, press and hold the reset button (usually labelled R on Vokera models) for 3–5 seconds until the fault indicator stops flashing. Release and allow the boiler to complete its start-up sequence. It may perform a brief venting cycle — this is normal.
- Monitor pressure over the following days DIY safe
Check the pressure gauge daily for three to five days. A single top-up that holds steady suggests the pressure drop was a one-off event, such as after bleeding radiators. If the pressure falls again within a few days, there is an underlying issue — a leak or expansion vessel fault — that needs professional attention.
- Call a Gas Safe registered engineer if the fault returns or pressure keeps dropping Gas Safe engineer
Persistent or rapidly recurring low pressure points to a leak, a failed expansion vessel diaphragm, or a faulty pressure sensor — none of which are safe or practical for a homeowner to fix. A Gas Safe engineer can pressure-test the system to locate any leak, re-charge or replace the expansion vessel, and test the pressure sensor. Do not keep topping up indefinitely without investigating the root cause, as undetected leaks can cause damage to floors, ceilings, and the boiler itself.
Parts you may need
- Expansion vessel (replacement) · from £80
- Expansion vessel Schrader valve · from £8
- System pressure sensor · from £35
- Filling loop assembly · from £20
- Automatic air vent · from £12
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–£350, depending on the underlying cause.
Frequently asked questions
What is the difference between Vokera fault codes A41 and A40?
A41 is a transitional warning — it appears when pressure drops below 0.3 bar and gives you a 10-minute window to act. If the pressure is not restored within that window, the boiler escalates the fault to A40, which is a full lockout and will prevent the boiler from firing at all. Fixing the pressure and resetting should clear both codes, but A40 may take a firm reset to dismiss once it has latched.
Can I fix the Vokera A41 fault myself?
Yes, in many cases. If the pressure gauge confirms the system is below 1 bar when cold, you can repressurise it yourself using the filling loop and then reset the boiler. This is a straightforward DIY task and no Gas Safe registration is required. However, if the pressure drops again within a few days, you should call an engineer to find the underlying cause — repeated top-ups mask a leak and are not a long-term solution.
Why does my Vokera boiler keep losing pressure and showing A41?
If A41 keeps coming back after you top up the pressure, the most likely causes are a water leak somewhere in the system (at a pipe joint, radiator valve, or inside the boiler itself) or a failing expansion vessel whose internal diaphragm can no longer hold pressure correctly. A Gas Safe engineer can carry out a system pressure test to pinpoint a leak and can check the expansion vessel pre-charge pressure. Expect to pay roughly £150–£350 for an expansion vessel repair or replacement, or £100–£300 to trace and fix a minor pipework leak.
Could a faulty pressure sensor cause the A41 code even if my pressure looks fine?
Yes, though this is less common. If the pressure gauge reads a normal 1.0–1.5 bar but A41 still appears, the pressure sensor that feeds data to the PCB may be giving a false low reading. In this situation, topping up and resetting will not resolve the fault. A Gas Safe engineer can test the sensor output and replace it if needed — sensor replacement typically costs £100–£250 including labour.