UK trade guideBoiler Spares 5 min readUpdated 11 July 2026

How to Replace the Primary Heat Exchanger on a Vokera Compact 29A (UK)

Step-by-step UK guide to replacing the aluminium/stainless primary HEX on a Vokera Compact 29A. Part numbers, torques, commissioning.

Vokera

The part

Replace the primary heat exchanger on Vokera Compact 29A when you see combustion products blowing back, F62/L9 faults or sooting on the burner.

Isolate safely

Drain and cap all four connections on Vokera Compact 29A. 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 Vokera Compact 29A 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 Vokera Compact 29A 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 Vokera Compact 29A is in warranty — Vokera require log of any part swap for labour claims.
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