How to Replace the Primary Heat Exchanger on a Ravenheat CSI Primary 85T (UK)
Step-by-step UK guide to replacing the aluminium/stainless primary HEX on a Ravenheat CSI Primary 85T. Part numbers, torques, commissioning.
The part
Replace the primary heat exchanger on Ravenheat CSI Primary 85T when you see combustion products blowing back, F62/L9 faults or sooting on the burner.
Isolate safely
Drain and cap all four connections on Ravenheat CSI Primary 85T. 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 Ravenheat CSI Primary 85T 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 Ravenheat CSI Primary 85T 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 Ravenheat CSI Primary 85T is in warranty — Ravenheat require log of any part swap for labour claims.
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