Low
P.4 on Vaillant ecoTEC Plus 625

Your boiler is currently running a safety program to remove trapped air from the internal pipes and heat exchanger.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

What the manual says

Manufacturer manual

Not available

From this model's manual
Verified against the Vaillant Ecotec Plus 615 installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

This occurs when the boiler detects potential air pockets within the internal pipework or heat exchanger, often following a recent repair or after the system has been refilled. To prevent damage from overheating, the boiler automatically runs a five-minute venting cycle to push any trapped bubbles out through the automatic air vent. It is a protective measure rather than a breakdown, ensuring the system is primed and safe to fire up.

This is more common in autumn when homeowners top up their system pressure or bleed radiators for the first time after the summer break.

DIY fix possible

Wait for the program to finish, as it usually stops automatically after 5 to 10 minutesEnsure all radiator valves are fully open to help move air through the systemCheck the boiler pressure gauge and top it up to 1.5 bar if it has dropped

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