Boiler pressure loss

[alchemy]

I have an Ideal Response 120 boiler. A few weeks ago it began leaking water when hot , and I called the engineers. They diagnosed faulty expansion vessel , pressure relief valve and the brass air vent on top of boiler. All these items have now been replaced. Now, the boiler works but it loses pressure once or twice a day i.e I top it up to 1.0 bar , use the hot water and central heating , then later in the day after it has cooled down I find it has dropped to just under 0.5 bar.

I cannot see any water dripping out of the boilers overflow pipe outside the house...
I have taken up flooboards this weekend and have inspected all radiator connections and I can't find any leaks in the system.

I wasn't losing pressure like this before the work was done on my boiler.
I don't really understand these things, but can this be because the expansion vessel hasn't been precharged properly or is not keeping it's pressure?
What I don't get is that water must must be coming out somewhere (I'm putting more in each day) but I don't see where ...

Can anyone tell me what could be causing this problem?

( All I do know is that my water pressure is low and my blood pressure is getting higher )

 

[bobw1956]

It,s possible that the heat exchanger is leaking,and the water is turning to steam,within the hx,hence no visible water leak.
you need an RGI to confirm this.

 

[Einstein]

The expansion vessel for this boiler can simply be checked and "pumped " back up to 0.85 bar (12 psi.). It is at the top right hand side of the boiler with its own small cover (3 screws). It is an ordinary schrader valve and can be pumped with a footpump held in hand .
If the heat exchanger is faulty after the boiler has cooled any water leaking which would normally go to steam will be settles at the bottom of the fan housing at the base of the H.E. It is easy to checkl. If it is the H.E. then taht will cost £250 to replace for the part alone.

 

[Einstein]

To add to my message excuse the original spelling. Any pumping up of the heat exchanger rubber diapragm should be done only if you are competent to do so and then only when the pressure on the water side has been relieved to zero. If its the heat exchanger which seems likely as this model has a bad record, then you must get in an Engineer.Incidentally the "overflow" pipe you refer to, is the excess from the pressure relief valve and normally should not leak or drip unless the system has exceeded 3 bar on your gauge.