Dropping pressure gauge

[Wexbike]

I’ve looked through the answers but I’ve not seen a solution to my problem. My pressure gauge drops overnight 1.75 bar to zero. No visible leaks any where …valves..connections pressure release valves etc. All radiators heating correctly and no air in rads. Circulation pump has no sounds of air gushing inside. automatic air vent close bye the boiler working normally no leaks no signs of water releasing. To re pressurise the system it literally takes a quick flick of the filling valve to get to the correct working pressure. Over the last couple of weeks I put two cans of tec7 sealer into the system. But no good. If I leave the circulating pump running without the boiler running the pressure remains constant.
Please does anyone have anything else to try

 

[SimonG]

Yes, stick a bag or bottle over the pressure relief valve discharge outside. Will confirm an easy fix.

 

[Wexbike]

Yes, stick a bag or bottle over the pressure relief valve discharge outside. Will confirm an easy fix.

Thank you I’ll try that, I have sealed system With only have a prv and doesn’t seem to have any leaks. It’s the fact the pressure stays up and remains constant with the pump running and the burner off. That’s the puzzling thing.
At night with the heating running pressure is constant but drops to zero when I look in the morning.
Thank you

 

[Chuck]

Thank you I’ll try that, I have sealed system With only have a prv and doesn’t seem to have any leaks. It’s the fact the pressure stays up and remains constant with the pump running and the burner off. That’s the puzzling thing.
At night with the heating running pressure is constant but drops to zero when I look in the morning.

To me, the symptoms you describe suggest an empty, failed or failing expansion vessel. Your observation:

"To re pressurise the system it literally takes a quick flick of the filling valve to get to the correct working pressure."

is the clue here. If you know what you are doing, as temporary test/fix you can bleed a couple of litres of air into a radiator to see if it helps.

 

[Wexbike]

To me, the symptoms you describe suggest an empty, failed or failing expansion vessel. Your observation:

"To re pressurise the system it literally takes a quick flick of the filling valve to get to the correct working pressure."

is the clue here. If you know what you are doing, as temporary test/fix you can bleed a couple of litres of air into a radiator to see if it helps.

Thank you for that. I guess just let off a few litres out of the system with the bleed screw open. The pressure vessel is about two years old. It’s not like a pressure vessel that you can pump to pressurise. You can’t see much but I enclose a photo of the tank. May I ask if it’s just the expansion tank where does the drop in pressure go. Thank you very much.

 

[SimonG]

T'other end, there'll be a Schrader valve. But need to dump pressure to get a true reading.

 

[Wexbike]

T'other end, there'll be a Schrader valve. But need to dump pressure to get a true reading.

I’ll certainly give it go. I can just about see a blue cap on the other end. I’ll remove the pipe in the picture and I’ll be able to get to it. But if the heating system is sealed with no leaks if the water is passing throu the internal diaphragm would the pressure not stay roughly the same as seen on gauge?? Thanks Simon