Pulsacoil 2000 no hot water!

Hi
My son has just moved into a flat which has been empty for 15 months. He is actually a newly qualified plumber but has not had any experience with Pusacoil type water storage. he had no water at all until he unseized the pump with a screwdriver then for 1 day only using boost he had hot water- now nothing again. Green light on outside of cabinet is on, red fault light is off. On the pcb red light flashes 2 times then gap then 2 times etc. After all expense of moving -the costs I have been quoted without even seeing the thing means he wont be able to eat for a month! just wondered as he is confident with gas boiler and HW systems whether someone could give suggestions then he could try to fix it himself- looking at other posts if it is likely to be the pump then he said he can change that himself. thanks from an 'empty nester' and skint mum!!
PS unit is warm!!

Unit needs to be hot!
When hot try it then.
There are lots of posts on here ref PC 2000's.
Mike
MGC/H2O
Norfolk

Tell your son to check the thermostat rods and elements. Confirm supply is coming to the element.