How to Replace the Flow Sensor on a Main Eco Compact 25 (UK)
Step-by-step UK guide to replacing the DHW turbine / flow sensor on a Main Eco Compact 25. Part numbers, torques, commissioning.
Main
The part
Swap the DHW turbine on Main Eco Compact 25 when hot water runs cold at low flow or the boiler fails to fire on demand.
Isolate safely
Isolate cold mains at the boiler's blue isolator. The sensor on Main Eco Compact 25 clips into the hydraulic block with two retaining clips.
Fit and commission
Fit new O-rings and align the turbine so the flow arrow matches the cold mains direction.
Recommission checklist
Refill the Main Eco Compact 25 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
- Can I clean rather than replace?
- Yes for a limescaled unit — soak the turbine in citric acid, but replace if the Hall-effect PCB is corroded.
- What minimum flow triggers?
- The Main Eco Compact 25 typically ignites at 2.5 L/min. Below that, check the aerator on the DHW outlet.
- Do I need to notify the manufacturer?
- Only if the Main Eco Compact 25 is in warranty — Main require log of any part swap for labour claims.
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