Noisy Baxi 105 he instant

19 Jul 2010
Reaction score
United Kingdom
I have a 3 year old Baxi 105he instant with a noise problem. After using hot water demand, eg shower, and the water is turned off, the boiler goes into a frenzy of gushing and squelching sounds for about 2-3 minutes. The pressure gauge drops about a third of a bar to .75 while this is happening. I have turned off the pre heat function on the boiler controls, as this used to cause the boiler to make the same noises, sometimes waking me up in the night! Any help would be greatly appreciated. Ta
Sponsored Links
sounds like you have air in the boiler ! have a look through the older posts there was one about this a few days ago ! ;)

Oh yes if its a whistling or screeching noise then it will be the diverter valve causing this !
Thanks for your reply Gaz. I unscrewed the black plastic screw on top of the aav,some air came out for a while but the noise still remains. I noticed some green gunge on top of the brass aav unit.
How do I tell if the vent needs replacing,can it be removed and cleaned? Do I need to drain down to replace this?
By the way, all the noise seems to be coming from the plate heat ex.
Sponsored Links
I have increased the water pressure to 1.5bar and slackened off the aav bleed screw and the noise is 90% gone now :)

A final question, does this bleed screw need to be permanantly slackened off? As it was tightened up when found..

Many thanks for all quick responses
the aav cap should be left loose - not fully tightened

check your expansion vessel charge as this if flat can cause the aav to leak a little (scale around it)
Will do, all seems good now, once again thanks for everyones help. This forum works!
How did you check the expansion vessel charge??

To do it properly, you need to isolate the boiler from the rest of the system by closing the F&R valves and draining the boiler. With the drain still open, check the air pressure on the schraeder and then inflate with a compressor or foot pump to likely 0.8 bar. You will see water being forced out of the drain as the EV bag inflates. You should have pressure in the EV and 0bar in the boiler. Close the drain and open the F&R valves, vent and refill, bleed the pump and aav.

If you check the pressure of the EV when the boiler is pressurised, you will be reading the boilers pressure.

Bleed your rads too, as the primary loop in the boiler will trap it when the divertor valve closes of the heating, for a HW demand, and just boil in the HE. Steam gurgles and thats what you will be hearing.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links