Medium
304 on Atag iS System

Your boiler has been manually reset too many times in a short period and has temporarily locked itself for safety.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

Too many resets

From this model's manual
Verified against the Atag Is System installation & service manual, page 72.
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

Turn the boiler power off at the fused spur switchWait for at least 5 to 10 minutes to allow the internal timer to clearTurn the power back on and see if the code has cleared

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 304: 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

101View →133View →110View →

Related guides you might find useful

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →

Pilot light keeps going out

Older boilers — thermocouple, draught, gas supply.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →