Baxi boiler - Replacing Expansion Vessel

I think the expansion vessel on our baxi boiler has gone, or at least needs recharging, as the pressure when running the central heating rises to about 3 bar

It then switches off due to the pressure then being 0 bar, this can be anything from 6 hours to 12 hours plus, so there is no set factor in how long it takes to drop to zero

Can anybody suggest how the hell I take the top plate and flue off so I can change the expansion vessel, I had a look at this last time when the air motor was making a terrible racket which turned out to be knackered rubber mounts making it vibrate on its mountings, I had to fix these in situ as I could get the top plate off no matter what I removed that looked like it was holding it all in place


I need to remove the flue so I can slide the expansion vessel out the back and drop a new one in, assuming it won't recharge and the diaphram has gone

Its fitted in a bedroom so access is very good all round


The boiler is roughly 3/4 years old



Thanks for any help, a manual would help greatly

Presume its an 80e / 105e?, there is a bar over the expansion vessel held by 2 screws at each end. Take this off and the valve will be under that. Under the boiler on the right hand side next to the pump is a drain tap, if you attatch a bit of tube and run it into a large bucket as you top up the pressure in the expansion vessel with a foot pump you will get an accurate reading. Forgot peeing about with the flue.

Many thanks

Yes, its an 80/105 baxi, and I can see the valve without touching anything a sits handly poking out through an access hole in the top bar with the valve cap still on it


But if I do end up having to change the expansion vessel, how would I remove the flue to slide the vessel out, and thanks for the drain tap suggestion

I would also want to shove in some corrsion preventer, is there an easy-ish way to do this



Swapping and rebuilding big heavy bike engines is more my pleasure than convincing boilers to run correctly

first retry recharging the vessel, you still need to depressurise the system to do this.

if you do need a new expansion vessel, then you may wanna think about installing a new one, elsewhere, to save getting old one out.

IF IT'S AN INSTANT (FITTED WITH A PRE HEAT FUNCTION) you can't fit an external pressure vessel as the one fitted has 2 water connections to it.

Yes he can. We fit external expansion vessels all the time to instants (customer allowing).....and isn't anyone on here worried when the OP says he intends to remove the flue??!!!.......call a gsr if thatr is what you intend to do my friend. Might save your life.....and your families

powell30 said:

Yes he can. We fit external expansion vessels all the time to instants (customer allowing).....and isn't anyone on here worried when the OP says he intends to remove the flue??!!!.......call a gsr if thatr is what you intend to do my friend. Might save your life.....and your families

Click to expand...

ollski said:

Presume its an 80e / 105e?, Forget peeing about with the flue.

Click to expand...

You can replace it with an external but you will lose your preheat. I'm almost certain the mi's say not to so I'm surprised a manufacturer does it.

Mi's dont say not to fit an external one cos they even make a kit for you to fit one and the preheat would be even better as the whole of the expansion vessel would be filled with preheat water rather than half water and half air

Assumung it's a 105e then the manual tells you that you will have to remove the boiler from the wall to replace the expansion vessel. Great design!

The plumber who replaced mine whipped out the air pressure assembly so he could get access to the pipe underneath the vessel to disconnect it, then the new vessel could be slid into place.