losing water pressure on Vokera compact boiler

[mg40]

Have a vokera compact boiler keep losing water pressure when heating isn't on and system shuts down ( get red light on over night so cold house in morning). Had this problem a few years ago ( don't believe its a leak) and cant remember what problem was believe it could a valve that's worn or something to do with heat exchanger. can any one help me work out whats wrong before i spend a huge amount of money getting engineer out to tell me.

 

[petej]

If you are losing pressure then it has to be a leak !
Either it is on the system -- radiators, radiator valves or pipe work or more likely it's the pressure release valve (PRV) fitted in the boiler.
This is not uncommon and as it should be terminated outside the house it is not always noticed. Tape a plastic bag over the end of this pipe so rain cannot get in (the bag) and it will show if this is where the water is going.

If water is coming from here it may just be a faulty PRV but a common cause of the PRV operating is that the pressure in the boilers expansion vessel has fallen leaving nowhere for the hot water to expand into, if you are lucky it just needs topping up (with air) but if water has got through the diaphragm and into the air side then the vessel will need replacing.

Pete