Good evening folks, I have a Ferroli C24 combi LPG boiler, i have had to take it apart to clean the heat exchanger as there was no water flow, but there was CH water flow. once i put it back together i now have water flow but it's not hot unles the CH is going but then its only warm. i did take the HW senor off and i cleaned a white residue off that i thought was a residue from the copper pipe but now i am wondering if it was not a gel for the sensor. It may be a simple sensor replacement but before pay for the Ferroli spanish plumber to come and shrug his shoulders like he normally does i could do with some suggestions. the CH and the HW go into different sides of the heat exchanger and from what i can see there is no diverter valve if that helps Thanks for any help.