Low water pressure indicator Ariston Eurocombi?

I have an Ariston Eurocombi boiler (A/23 MFFI) which has decided to stop working. The 'low water pressure' indicator has lit up- but the gage shows 1.5 bar - which should be perfect. I've taken it right up to 2.5 bar, then drained the system down to nearly zero, then back up to 1.5 in a bid to try and reset it - but still this indicator remains lit with no other sign of life from the boiler. Have also switched it on & off from the mains - no joy. Every time i turn it on, it remains completely silent for 1 minute and then stubbornly lights up the 'low water pressure' indicator. Any suggestions anyone?