eh ? 🙁

It’s only a schraeder valve, and I’ve used those once or twice before. Can the bladder/membrane/whatever have fused together or something ?

Story is that I am pretty well certain that the tank is full of water, no air gap. I am also unable to get water or air to come out of the valve when there’s pressure in the CH system (which, I believe means it’s full of water but the bladder isn’t breached)

so why can’t I inflate it ?
(I’ve changed the valve core; no different. Currently left with pump attached and with a bit of pressure in the hose to see if I can get it to “separate”)

Tried using a shock pump with pressure gauge? Pressure should go up when you pump. System pressure is usually 2 to 3 bar.

It is most likely the bladder has split.

Valve might be jammed, I had this with the boiler in my last house. I used the valve core out of a MTB inner tube to replace it with and it was ok.

If the system is pressurised you’ll be battling against the pressure of the water when you try and pump it up. Try draining some water out of the system before pumping it up then repressurise.

Thanks, but:

Tried using a shock pump with pressure gauge? Pressure should go up when you pump. System pressure is usually 2 to 3 bar … it’s most likely the bladder has split

yeah, pump shows psi but that’s the pressure in the hose. I can take off the pump and when I depress the valve pin a TINY bit of air is relaeased – so little that I suspect it’s all in the valve body. The websites tend to suggest that a split bladder would see water coning up out of the valve but it doesn’t even when there’s decent pressure in the system

Valve core might be jammed … If the system is pressurised you’ll be battling against the pressure of the water when you try and pump it up. Try draining some water out of the system before pumping it up then repressurise.

Core was fine, though I replaced it anyway. System pressure reads ZERO when I’m trying to pump up (and that gauge is working). I’m not fighting against moderate resistance here; it’s absolute

Are you sure it’s the CH expansion tank (red), not the DHW (white or blue)? DHW will be at mains pressure, plus there should be a check valve to prevent backflow.

yeah, it’s the CH – I can de-pressurise it by bleeding a rad

Odd that the pressure doesnt change.
I know I had issues with our CH over-pressurising and triggering the bypass valve.
Turned out the system had been overfilled so although the bladder was at the correct pressure, the air volume was far too low. IIRC when you pumped it up to pressure, the CH water pressure gauge went up (it should remain at zero). I sorted that by draining about 8 litres from the system, pressurising the bladder and then re-filling the system to the correct pressure. No issues since.
Perhaps it might be worth partially draining the system first?

Yeah, dump some water, remove the valve core again and poke through the hole where the valve goes ( could be some crap in there) and try again.
Fingers crossed!

Try the connecting pipe to the system, this blocked on me,

remove the valve core again and poke through the hole where the valve goes ( could be some crap in there) and try again.

going to try that as a last resort (I assume there’s a risk of puncturing the membrane but if I’m about to replace it all, who cares ?

(it’s not a need for drainage – there is literally zero pressue in the system, that’s what the gauge says and I can take the valve core right out without anything exiting the hole)

Change the valve core for another from an inner tube.

My grant expansion vessel needed that before I could inflate it with the track pump

Change the valve core for another from an inner tube.

yeh, did that before starting the thread – no luck

however I (and markrh) own the plumbing world outright. Valve out and a firm prod with a suitable allen key down the hole and we’re away ! 😀

WELL DONE EVERYONE* !!

(just me and him really)

Yay! Glad to help.