On 07/04/2021 23:37, John Rumm wrote:
On 07/04/2021 18:07, Tim+ wrote:
Our mains pressure HW system has an external expansion vessel.

Lately its not being doing its job and water has been trickling through
the pressure relief valve whenever it was heating up.

I had tried unsuccessfully to recharge it with my bicycle track pump
but I
ended up convincing myself that the internal rubber bag had failed.

Anyhow, took the bull by the horns today and depressurised the HW system
and undid the pipe connection.Â* I then unscrewed the securing jubilee
clips
that hold it to the wall bracket.

**** me but the holding it up with one hand in the top of the airing
cupboard and trying to lift it off the pipe work was not happening!
Managed
to undo another pipe joint and to free the unit and then dragged it
out of
the cupboard.

Turned out of course that it was still full of water and at about 30cm
wide
and 40 cm tall it would hold around 28L!

With hindsight I should obviously have let air into the top of the
tank to
allow it to drain. Wont make that mistake again!

The bag actually seemed fine and once reinstalled and re-pressurised to 3
bar there was no evidence of any leak.

The normal procedure for checking and re-pressurising is to:

Turn off mains cold inlet to cylinder.
Open a hot tap somewhere - water will drain until any water in the
expansion vessel is expelled.

Now check the pressure at the shrader valve. If it's less than
(typically) 3 bar, add air until it's at 3 bar.

Close the hot tap, and open the inlet valve to the cylinder.

I added some notes to the maintenance section:

http://wiki.diyfaq.org.uk/index.php/...g_requirements


Only for unvented DHW though. For combis, or "system" boiler with vented
DHW you need "my" method. I must admit I had not noticed when I posted
earlier that Tim has unvented DHW.