PRN

Hi, could someone advise, we had an Ei168RC (only one unit) installed as part of a new kitchen build in 2016. It has just started to chirp approx every 10 seconds or so. I've tried to reset by holding down the test button for about 10s, but no luck. I've shut off the mains to it and reconnected bu, again, no luck. Can anyone help? My wife is self isolating at the moment, so I don't really want the risk of having trades in the house. Thanks in advance