Im baffled with this drop in pressure

[kevhky]

This is totally baffling me

Combi boiler
i top the boiler up (ch) to 1 bar, after around 24 hours the pressure drops to zero (heating running throughout via room stat)

I then top boiler up (ch) to 2 bar turn heating completely off for 24 hours and no loss in pressure

During this time dhw is being used

I check everywhere for leaks no sign what so ever pipework/prv/rads under boiler absolutely nothing at all

Scratching my head with this one

 

[Gasman77]

Any pipes screeded in the floor?

 

[kevhky]

Any pipes screeded in the floor?

No, all under floorboards

 

[markymark1234567]

Sound like the pressure vessel is knackered. Feel the prv pipe see if it gets warm or find where it terminates outside i bet it is wet.

 

[Gasman77]

Downstairs too? you need to let the system go cold as it will be evaporating when hot

Also try isolating the boiler over night and see if it drops - if it does you know the leak is in there!

 

[Gasman77]

The OP said he checked the prv!

 

[kevhky]

Sound like the pressure vessel is knackered. Feel the prv pipe see if it gets warm or find where it terminates outside i bet it is wet.

Prv is dry as sticks outside

 

[kevhky]

Downstairs too? you need to let the system go cold as it will be evaporating when hot

Also try isolating the boiler over night and see if it drops - if it does you know the leak is in there!

I let the system go cold overnight, then topped it to the 2 bar, 24 hours later still sittin at 2 bar,

both upstairs and down all pipework runs under beams

 

[Blackadder43]

Just to 100% take the prv out of the equation stick a ballon over the end of the pipe while you are running the heating........

 

[kevhky]

Just to 100% take the prv out of the equation stick a ballon over the end of the pipe while you are running the heating........

ive done that and not a drop in sight

 

[Blackadder43]

Then its methodicaly check every pipe run as soon as the pressure drops.....
Good luck

 

[doitall]

Could be the plate HX is pin holed.

Does the gauge go up and down if you open and close a hot tap

 

[DP]

John, that is not possible.

 

[twgas]

Just to 100% take the prv out of the equation stick a ballon over the end of the pipe while you are running the heating........

ive done that and not a drop in sight

I dont think you tried this for long enough (34mins between suggestion and your result post). try it again, for 24 hours, from cold @ 1bar, and watch the pressure gauge as the system heats up.