hello chaps,i have a ferroli optima 901 combi boiler that looses pressure and drains the water out of the system to the outside drain.i had the automatic air vent & c/h safety valve changed last year,and the safety valve changed again this year by a plumber,if the system is running heating or water the pressure drops quite quick,ie a few hrs,if not in use it lasts a day or more,my Q is. is the problem still with these parts,the boiler is 10yrs old now and i dont want to throw money at it,i would sooner have it replaced.if i do would it be best to change to a condensing boiler,i have a 2 bed bungerlow with 5 convector rads with thermostats and a towel rail.the boiler sits in the loft.thanks for looking and advise.
If it's definately losing the water to outside, it could be a few things.
1) The combi fill / filling loop is not fully closed, the system may be filling slowly until it reaches 3 bar then the PRV will open.
2) The PRV is passing, renew pressure relief valve.
3) The expansion vessel isn't taking up the expansion - check to see if the pressure rises to above 3 bar when the heating is on. You may be able to re-pressurise the vessl to 1 bar witha foot pump, if not it needs replacing.
4) The plate heat-ex is mixing the water, the water from the mains is topping up the heating side - water is discharged via PRV, when it gets to above 3 bar.