P 0.9 Low

Potterton P 0.9 Fault Code

Also written as P09 — same fault.

The Potterton P 0.9 fault code means: your boiler has noticed that the water pressure is getting a bit low and needs a small top-up to keep running efficiently.. It appears on 1 Potterton model in our database.

Monitor it

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: System pressure is falling. It is advised to top up the pressure (status display will flash).

What causes the Potterton P 0.9 fault?

This fault occurs when the water pressure inside your heating system drops below the ideal operating level. The most common reasons are small leaks from radiator valves, air being released through the vents, or the expansion vessel losing its air charge over time.

This issue is frequently seen in autumn when the heating is turned on for the first time after summer, as the change in temperature can highlight minor leaks or trapped air.

Typical repair cost £0-80 (including labour)

DIY fix possible

Locate the filling loop (usually a silver flexible hose) underneath or near the boiler.Slowly open the valve(s) until you hear water entering the system.Watch the pressure gauge and close the valves tightly once it reaches 1.5 bar.

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Potterton models that show the P 0.9 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Potterton P 0.9 fault code information on this page is sourced and cross-checked against the official Potterton service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026