Your boiler is currently pumping away waste water, which is a normal part of its operation and doesn't necessarily mean there is a fault.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: This indicates that the Condensate Pump is running. The pump ONLY runs when the condensate reservoir is full.
What causes this fault?
This occurs when the internal collection tank becomes full of waste water produced during the heating process. The pump is physically triggered to move this liquid away from the boiler and into a drain. It is a sign that the mechanical float or sensor has reached its limit and is working exactly as intended to prevent an overflow.
This is more common during very cold spells, as external drain pipes can freeze, causing the pump to run more frequently or struggle to clear the water.
DIY fix possible
Observe the light for a few minutes; it should turn off once the water has been drained.If the light stays on indefinitely, check the external white plastic pipe for blockages or ice.Ensure the pump's discharge hose isn't kinked or restricted.
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A boiler cover plan would cover faults like Condensate Pump (Green Light) — no call-out fees, no surprises.
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