What A40 means on a Vokera boiler
A40 is the low pressure lockout on the Vokera Easi-Heat i 25C and 29C. The fault table in section 3 of Vokera's Easi-Heat i users and installation instructions (document 20195442, edition 3) gives the description as "Fill the system" and marks the code as definitive. Definitive means the boiler stays locked out until someone puts the pressure right and resets it. It will not clear itself the way a temporary warning does.
The boiler measures the heating circuit with a water pressure transducer. The manual explains that this transducer switches off the pump, fan and burner if the pressure drops below the rated tolerance, which protects the heat exchanger and pump from running short of water. So with A40 showing you will have no heating and, as the Easi-Heat i is a combi, no hot water either.
How A41 turns into A40
A40 does not appear the moment pressure dips. The manual describes a two stage warning:
- If the pressure falls below the 0.3 bar safety value, the boiler shows A41, also described as "Fill the system", for a transitional period of 10 minutes.
- If the pressure is still too low after those 10 minutes, the code changes to A40 and the boiler locks out.
That gives you a short window. If you spot A41 and top up straight away, you can often avoid the lockout altogether. The fault table also lists a "FIL" signal for low pressure and a separate signal when the pressure goes above 3.0 bar, so the display may warn you before either code appears.
| Display | Meaning in the Easi-Heat i manual | What to do |
|---|---|---|
| FIL | Low pressure, check system | Top up to 1 to 1.5 bar |
| A41 | Fill the system (transitional, 10 minutes) | Top up now to stop it becoming A40 |
| A40 | Fill the system (definitive) | Top up, then hold reset for more than two seconds |
| A42 | Pressure transducer fault (definitive) | Gas Safe registered engineer |
| Above 3.0 bar | High pressure, check system | Do not top up; see below |
Older Vokera models use A04
If your boiler is a Compact A, Unica i or another older Vokera, low pressure shows as A04, described as "insufficient system water pressure". The fix is much the same, but those boilers reset with the mode selector knob, so our Vokera A04 page is the better guide for them.
How to top up an Easi-Heat i and clear A40
The Easi-Heat i manual notes that the filling loop is not supplied with the boiler, so your installer will have fitted one. These steps follow section 2.13 of the manual:
- Turn the heating off and let the boiler cool.
- Find the filling valve connections, usually beneath the boiler.
- Attach the filling loop to both connections if it has been removed.
- Open the filling valve slowly until you hear water entering the system.
- Watch the pressure. The display shows it in standby, and it is also item I018 in the Info menu. Close the valve when it reads 1 to 1.5 bar.
- Remove the filling loop, with a cloth ready for a few drips.
- Hold the reset key for more than two seconds. If the right conditions have been restored, the boiler starts again.
For the pressure figures across other Vokera models, see our Vokera boiler pressure guide.
Do not overfill. The manual gives a maximum working pressure of 2.5 bar, and the pressure rises as the water heats. Stopping at 1 to 1.5 bar cold leaves enough headroom.
Why the pressure dropped
The manual's own cause for A40 is simply low system pressure. The useful question is where the water went:
- Bleeding radiators or draining down for plumbing work lets water out on purpose. One top-up afterwards is normal.
- Slow weeps at radiator valves, towel rails or hidden joints add up over weeks.
- The pressure relief valve lets water out through its discharge pipe if the pressure rises too far when hot, usually because the expansion vessel has lost its charge.
- An internal leak shows as water under the boiler. Look, but do not open the casing.
The manual says that frequent pressure loss may mean a leak, and that you should ask your installer to inspect the system. If the pressure drops very often, it tells you to contact Vokera's Technical Assistance Centre.
Why A40 matters more in winter
The Easi-Heat i has built-in frost protection that runs the burner or pump when the boiler temperature falls below 5°C. The manual says this relies on a permanent electrical supply and on the boiler not being in a fault state, and that it protects the appliance only. A boiler left locked out on A40 through a cold spell is not protecting itself, so top up and reset promptly rather than leaving it until the weekend.
When to call a Gas Safe registered engineer
Book an engineer if A40 returns within weeks of a top-up, if you see water dripping outside or under the boiler, if the pressure climbs above 2.5 bar when hot, if the display reads a healthy pressure but A40 will not clear, or if A42 appears. The engineer will normally check the expansion vessel charge, the relief valve, the visible joints and the transducer reading. Tell them how often you have topped up and the readings you saw.
Never remove the casing to look for an internal leak or to touch the expansion vessel. Water inside the boiler sits close to live parts and the gas supply, so it is a job for a Gas Safe registered engineer only.
Typical repair costs in the UK
| Job | Typical UK cost |
|---|---|
| Topping up yourself | Free |
| Engineer call-out and diagnosis | Typically £60 to £150 |
| Expansion vessel recharge | Typically £80 to £150 |
| Pressure relief valve | Typically £100 to £200 |
| Pressure sensor (transducer) replacement | Typically £100 to £220 |
| Internal leak or pipe joint repair | Typically £100 to £300 |
For the other codes we cover, see the Vokera fault code hub.