hello new to this forum, not really a plumber but am good with a electronics. i have a problem with my boiler (ferrolli optima 1001) had a plumber out and he was useless, so i took a look myself. now what happens is when i put the shower on it gets mad hot and then goes freezing cold. when looking at the boiler when it goes mad hot it is on high flame then the flame knocks off and this is when it goes freezing cold, then it will fire back up and do exactly the same unto the cows come home. when it knock off the faults lights show its a dhw sensor. so i swapped the dhws with chs by just swapping the wires over(to check it wasn't the main cpu board) the shower worked fine and the ch was broke. i swapped them back over and thought it was the sensor its self i ordered a new one and fitted it. it still done exactly the same thing after fitting, i then checked the low flame and high flame pressure. low flame was 3bars and high flame was 15bars. i think this is correct. my next thought is the main CPU board, but why would it work when swapping the wires overs? if anyone has any ideas it would be gratefull! would be willing to return the favour for any electrical or security work!