Heating system pressure

[JBaill]

I have to top up the pressure on my sealed underfloor heating system off a conventional gas boiler. As the pressure increases by around 2 bar when at full temperature, I suspected the expansion vessel. The one internal tp the boiler has a normal bicycle valve which when depressed let out water. Can I assume the bladder is burst or might it be OK if I was to pump it up again - worth a go?
I have another expansion vessel fitted external to the boiler but can't find a fitting on it to charge the bladder. Am I being stupid and blind, or might it be a completely sealed unit?

 

[gas_man_gaz]

the one on ya boiler will be knackerd thats why you'll hav a remote one fitted (dependin on the boiler can be a right pain changing the exspansion vessel).. has the remote one got a black cap on the bottom? if it has unscrew it

 

[Gasguru]

An initial small quantity of water may not be a problem, all depends whether the valve is at the bottom of the vessel or not.

Have a look at the other vessel - sometimes the valve is hidden behind a large plastic cover. Try underscrewing the cover, otherwise prise it off...there will be a normal tyre valve underneath.

 

[bengasman]

The valve will be opposite to the pipe going into the external one