Viessmann EA Fault Code
The EA fault means system water pressure has dropped below the minimum operating threshold. It is the most homeowner-resolvable Viessmann fault — but only once you have confirmed there is no visible leak.
What is the Viessmann EA fault code?
The Viessmann EA fault is triggered when the pressure sensor detects the central heating system has fallen below the minimum safe threshold. The Vitodens 100-W and 200-W require a minimum of around 0.75 bar to operate — below this, the boiler locks out to prevent running dry and damaging the heat exchanger. In most cases, repressurising via the filling loop and resetting clears EA immediately. If pressure drops again within weeks, a leak or failed expansion vessel is the underlying cause.
What causes the EA fault?
All sealed systems lose a small amount of pressure over time — up to 0.2 bar per year is normal. Below the minimum threshold, the boiler locks out with EA.
A dripping radiator valve, weeping pipe joint, or leaking pump gland allows water to escape. Pressure dropping more than 0.5 bar within a few weeks of repressurising points to a leak.
A depleted vessel air charge causes pressure to drop on cooling — often falling below the EA threshold overnight. Common on Vitodens boilers over 10 years old.
Bleeding radiators releases water alongside air, reducing system pressure. Always repressurise after any bleed.
A stuck-open auto air vent slowly allows water to escape the system.
If both filling loop valves are not fully closed after repressurising, the loop can drain back and let pressure fall.
What you can safely check yourself
Find the pressure gauge on the Vitodens display or external gauge. Cold pressure should be 1.0–1.5 bar. Below 0.8 bar: repressurise. At zero: check for visible leaks before filling.
Locate the filling loop — typically a braided hose with two valves beneath or beside the boiler. Open both valves slowly until the gauge reads 1.2–1.5 bar. Close both valves fully.
Hold the reset button for 3 seconds. Watch the gauge over the next 48 hours. If it drops more than 0.3 bar within a week, call an engineer.
Do not reset the boiler more than once if the fault code returns immediately. Repeated resets without diagnosis can mask a worsening fault.
What needs a Gas Safe engineer
- Pressure test the system to locate any hidden leak in pipework, radiators, or fittings
- Inspect the expansion vessel — recharge with nitrogen if pressure is low, replace if membrane has failed
- Check automatic air vents and replace if weeping
- Inspect pump gland seals for dripping
- Check radiator valve gland nuts for slow leaks
- Replace filling loop or isolating valves if internal leakage is confirmed
Expansion vessel failures are common across South London. Thames Water's hard water accelerates corrosion of the rubber diaphragm inside the vessel. Viessmann Vitodens 100-W and 200-W boilers over 10 years old in Wandsworth, Merton, Lewisham, Lambeth, Southwark, Greenwich, and Bromley frequently develop expansion vessel faults alongside the EA code. Reion checks expansion vessel charge pressure on every annual service.
How much does a EA repair cost?
Costs below are UK averages. Reion provides a fixed quote after the £80 diagnostic visit — no obligation to proceed.
How to reset a Viessmann boiler showing EA
Repressurise to 1.2 bar via the filling loop before resetting.
Ensure both filling loop valves are fully closed after repressurising.
Hold the reset button for 3 seconds.
Monitor the pressure gauge — it should remain stable as the system heats.
If pressure drops again within days, call a Gas Safe engineer.
EA alone is very rarely a reason to consider boiler replacement. The exception is if a pressure test reveals a cracked heat exchanger as the source of the pressure loss.
Common questions about the Viessmann EA fault
Can I fix a Viessmann EA fault myself?
Why does my Viessmann boiler keep showing EA?
What is the correct pressure for a Viessmann Vitodens?
How much does a Viessmann EA repair cost in London?
How do I know if my Viessmann Vitodens needs a new expansion vessel?
Other Viessmann fault codes
Need a Viessmann engineer in London?
Reion is Gas Safe registered (919881), based in South London, and available 24/7. Fixed price after the diagnostic visit — no hidden charges.
