Your boiler has noticed the water pressure is slightly low or fluctuating and is performing a quick check to see if it can still operate safely.

DIY fix possible

Check the pressure gauge on your boiler or central heating system.If the pressure is below 1.0 bar, use the external filling loop to top it up to 1.5 bar.Ensure all radiator valves are open and bleed any trapped air from the radiators.Reset the boiler to see if the message clears.