Ferroli Modena 80E constantly running?

Hi Guys

Bit of an odd one - my Ferroli Modena 80E boiler just started running last week of its own accord. Now the pump is continually running with the burner cycling on for a few seconds now and then.

I have the demand for heating switched to off yet this still happens. My first thought is the frost stat - it feels like the boiler thinks it's very cold and bringing on the frost protection. Would that be the thermistor maybe?

I know a little bit about boilers but am no expert - any help much appreciated.

Thanks