Water Heater Fault

Hi all

I have a problem with my water heater, it works for so long then it goes into fault, once reset the heater will work for 5 mins again then go into fault again. Has anyone experieced a similar fault on their heater? We had our electronic unit replaced 18 month ago but that time the heater never worked at all.

Has anyone got a manual on these water heaters?

Manage to get a manual but it was the electronic unit which was faulty again, thats 2 in 18 months!

Does anyone know the reason for this? I was suspecting possibley power surges as the water heater & fridge/freezer are the only equipment left plugged in when the apartment is empty and I also have a problem with my freezer not working!