Baxi 105 Instant

10 Oct 2006
Reaction score
United Kingdom
:cry: Hi Guys/Girls
My Baxi 105 instants pressure gauge rises to over 3 bar when the heating is on and when you draw hot water or the pre heat comes on the pressure will drop about 0.5 bar. I have checked the expansion vessel and there is no water coming out of the vavle and there seems to be plenty pressure in there
anyone any ideas could it still be the expansion vessel and pre heat store Thanks in advance everyone regards. Cris
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Hi as I thought I was going to have to top the expansion vessel up I switched off the boiler and let it cool down then drained the system and disconected the filling loop to create an open end ready for putting air in the expansion vessel but when i took the reading it had 2 bar in it. I not quite sure what bar should be in there but 2 bar seems high enough i would have thought. any ideas ? could it be the pre heat store and the expansion vessel is ok ? I know they are both one part Thanks and your help is most welcome Chris
It is fairly common for the expansion vessels on these to go :confused:
if you have enough clearance at the top then you shouldnt have to take the boiler off the wall to replace it otherwise it needs to come off :rolleyes:
Just removing the filling loop should not normally depressurise the system. But you can tell from the boiler gauge which should read zero before you start checking the expansion vessel.

Normally the vessel should be charged to about 0.9 Bar and the system to 1.5 Bar afterwards.

If the diaphragm has failed then you will be unable to get any pressure into the vessel.

hi guys the pressure Vessel has pressure in it and seems to be holding I set it to 1 bar could it be the plate heat exchanger? :idea:
turn the boiler off over night with the preasure set to 1 bar. in the morning if it has risen then i would suspect the plate is passing....
Thanks Jason I have done that and the pressure remains at 1 bar. what else could it be ? its starting to drive me insane

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