Low
105 on Atag iS System

Your boiler is currently running an automatic air-bleeding cycle to remove bubbles from the system, which typically happens after a power cut or when first switched on.

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

Venting program active when power turned on or interrupted

From this model's manual
Verified against the Atag Is System 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.

DIY fix possible

Wait approximately 7 to 10 minutes for the 'filling and venting' cycle to complete automatically.Check that your radiators are bled and the system pressure is between 1.0 and 1.5 bar.If the code persists for over 15 minutes, try restarting the boiler via the on/off button.

Find a Gas Safe engineer
Search the official register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like 105: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

Related fault codes

106View →111View →117View →

Related guides you might find useful

Boiler won't turn on — 9-step checklist

Work through these before the call-out.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →