ATAG 612 Fault Code: Causes, Fixes & Repair Costs
What does the ATAG 612 fault code mean?
Fault code 612 on Atag boilers (including the iC, iS, and iR ranges) indicates that the boiler's fan has failed to start up when commanded to do so. The fan is a critical safety component: it draws combustion gases through the heat exchanger and expels them safely via the flue. Without confirmation that the fan is running correctly, the boiler's control board will prevent ignition entirely — so the boiler will not fire until the fault is resolved. In most cases the display will show '612' alongside a fan fault message.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or seized fan motor Common
Over time, the fan motor's bearings wear out or the motor windings deteriorate, preventing the fan from spinning at all. This is the single most common root cause of a 612 code, particularly on boilers that are five or more years old. A complete fan replacement is usually the appropriate remedy.
- Wiring or electrical connection fault Common
Loose terminals, corroded connectors, or damaged wiring between the fan and the PCB can mean the motor never receives the start signal — or that the control board never receives confirmation the fan is running. A Gas Safe engineer will inspect the wiring harness and connector block for signs of damage or poor contact.
- Physical obstruction blocking the fan Sometimes
Debris, insects, or other foreign material inside the fan housing can jam the blades and prevent rotation. Although less common in a sealed boiler, it does occur — especially on older installations or after building work nearby.
- Faulty PCB (printed circuit board) Sometimes
If the control board itself is defective, it may fail to send the correct start signal to the fan, or it may misread the fan's speed feedback and report a fault even when the fan is mechanically sound. This is diagnosed only after the fan and wiring have been checked and found to be in order.
How to fix it
- Check your gas supply is working DIY safe
Confirm that other gas appliances in your home (such as a hob or separate fire) are working normally. If there is no gas supply to the property, contact your gas supplier rather than investigating the boiler further.
- Reset the boiler once or twice DIY safe
Press and hold the reset button as described in your Atag user manual. Allow the boiler to run through its start-up sequence. If the 612 code returns immediately, do not keep resetting — repeated resets will not fix a mechanical fan fault and may mask the problem.
- Do not attempt to access or inspect the fan yourself Gas Safe engineer
The fan is located inside the boiler casing and involves electrical components connected to the control board. Removing the boiler casing, handling internal wiring, or attempting to spin or free the fan blades manually should only be carried out by a Gas Safe registered engineer.
- Book a Gas Safe registered engineer to diagnose the fault Gas Safe engineer
A qualified engineer will remove the boiler casing safely, inspect the fan motor, check the wiring harness and connector block, and test the PCB's output signals. They will confirm whether the fault lies with the fan itself, its wiring, or the control board before proceeding with any repair.
- Engineer to replace the fan if found to be faulty Gas Safe engineer
If the motor is seized, the bearings have worn, or the windings have failed, the engineer will fit a replacement fan unit compatible with your specific Atag model. On older boilers where the fan has completely failed, repair of the motor itself is rarely cost-effective — a full fan assembly replacement is the standard approach.
- Engineer to inspect and repair wiring if the fan is mechanically sound Gas Safe engineer
Should the fan spin freely by hand and show no obvious mechanical damage, the engineer will trace the wiring circuit, replace any damaged cables or connector blocks, and retest the boiler to confirm the 612 code is cleared.
- Engineer to test or replace the PCB if wiring and fan are both confirmed good Gas Safe engineer
If neither the fan nor its wiring is at fault, the control board will be tested using a multimeter to check that the correct voltage signals are being sent. A faulty PCB will need to be replaced — this is a more costly repair, and your engineer may discuss whether it remains economical given the age of the boiler.
Parts you may need
- Atag boiler fan assembly (replacement unit) · from £150
- Fan wiring harness / connector block · from £25
- Atag PCB (control board) · from £280
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £200–£350, depending on the underlying cause.
Frequently asked questions
Can I fix an Atag 612 fault code myself?
Not safely, no. While you can try a single reset and confirm your gas supply is on, the actual repair involves accessing internal electrical components inside the boiler casing. This work must be carried out by a Gas Safe registered engineer. Attempting it yourself risks electric shock, damage to the boiler, and could void your warranty.
How much does it cost to fix an Atag 612 fault?
For the most common fix — replacing the fan — expect to pay roughly £200–£350 all-in for parts and labour in the UK. The fan component itself typically costs £100–£200, with a Gas Safe engineer charging around £100–£200 for the labour. If the root cause turns out to be the PCB rather than the fan, costs rise considerably: a replacement control board can cost £280 or more for the part alone, plus labour, which may push the total beyond £500. At that point it is worth discussing with your engineer whether a new boiler represents better value.
Is an Atag 612 fault covered under warranty?
Atag boilers come with a standard 10-year warranty, during which Atag's own engineers attend to faults. However, the warranty requires the boiler to be serviced annually by a qualified engineer — missed services can invalidate cover. The warranty may cover parts but not necessarily labour, so check your specific warranty documentation carefully before booking an independent engineer, as using one during the warranty period could affect your entitlement.
Why won't my Atag boiler fire after I reset it — it just shows 612 again?
Fault code 612 is a safety lockout triggered because the boiler's control board cannot confirm that the fan is running. Until the fan is working correctly, the board will refuse to allow ignition — this is intentional, to prevent combustion gases building up in the flue. Resetting the boiler will not fix a seized motor, broken wiring, or faulty PCB, so the 612 code will keep returning. The underlying fault needs to be diagnosed and repaired by a Gas Safe engineer before the boiler will operate normally again.