Low
P.5 on Vaillant ecoMAX 635

Your boiler is currently running a brief, automated safety test to ensure its emergency heat-shutoff system is working correctly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Program for STB (safety temperature limiter) testing; the device heats up, bypassing the regulator shutdown procedure, until it reaches the STB shutdown temperature of 97 °C

From this model's manual
Verified against the Vaillant Ecomax 613 installation & service manual, page 50.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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