UK trade guideBoiler Spares 5 min readUpdated 11 July 2026

How to Replace the Primary Heat Exchanger on a ATAG i36 Combi (UK)

Step-by-step UK guide to replacing the aluminium/stainless primary HEX on a ATAG i36 Combi. Part numbers, torques, commissioning.

ATAG

The part

Replace the primary heat exchanger on ATAG i36 Combi when you see combustion products blowing back, F62/L9 faults or sooting on the burner.

Isolate safely

Drain and cap all four connections on ATAG i36 Combi. The HEX weighs 12–18 kg — get a second pair of hands.

Fit and commission

Torque new HEX unions to the OEM figure (typically 40 Nm for cast, 28 Nm for stainless) and refit new burner and door gaskets.

Recommission checklist

Refill the ATAG i36 Combi to 1.2 bar cold. Bleed high-point radiators and the internal AAV.

Run a full flue-gas analysis after 15 minutes. Log the reading against the OEM commissioning envelope in the Benchmark book.

Frequently asked questions

Warranty implications?
A HEX swap on an in-warranty ATAG i36 Combi must be logged with the manufacturer — otherwise the labour claim voids.
System clean first?
Mandatory — power-flush and fit a magnetic filter or the new HEX will block within two years.
Do I need to notify the manufacturer?
Only if the ATAG i36 Combi is in warranty — ATAG require log of any part swap for labour claims.
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