Stumped on this one shower goes colder for a second or so and then gets hot again,i have checked resistence on the elements both are 12 ohms.just to be 100% certain I had a spare unit around,removed the element,and after testing the resistence both again around 12 -13 ohms,swapped it still the problem is there.I have descaled both the head and hose.I have not checked the inlet filter mesh,but the pressure seems more than adequate.No low pressure light and flow seems constant as temperature drops off.Could the board be at fault ?.