baxi 105e instant expansion tank

[gest1221]

Hi can anyone help I have just fitted an external expansion tank to a back 105e instant combi but the new tank has a pressure of 1.5 bar and my system should be around 0.9 bar it is an 8ltr tank should I reduce the pressure in the new tank to 0.9 bar at the moment it holds pressure when dhw is in use but as soon as CH is on the pressure builds up in the system and prv opens at around 2.5 bar is it the extra pressure in the new tank that is causing problem or do I have another fault in the heat exchanger blocked plate heat exchanger seems okay good dhw flow.
Graham[/b]

 

[ianmcd]

where have you connected the new external expansion vessel to on the system ?

 

[gest1221]

Hi Ian the tank is connected on the system side of the fill loop just past the non return valve.
Graham

 

[twgas]

It would be sensible to set the air pressure as per the instructions, at least you would then know if there are any other problems rather than trying to best guess. 8 litres may not be big enough - depends on size of system

 

[ianmcd]

as Twgas says try lowering the vessel pressure to 0.8 bar even if just for your peace of mind, you can always pump it back up again, remember you must release the system pressure when adjusting the air pressure in the vessel, how many radiators do you have ?

 

[gest1221]

The system supports 7 rads so I will as suggested reduce the tank pressure to .8 bar and see how that goes for a few days thanks for the advice will post again in a few days to let you know what difference it makes
Graham

 

[ianmcd]

your vessel should be fine for 7 radiators

 

[Agile]

It still should absorb the pressure below 3 bar.

I am wondering if you have correctly measured the air pressure!

Some idiots just measure the air pressure when connected to the working boiler!

 

[gest1221]

The tank pressure is from manufacturer and shown on the side of the tank 1.5 bar I have not measured the actual pressure in the tank but as you say would have thought it would be OK well under the 3bar system max pressure.

 

[ianmcd]

No read the FAQ on here on how to check the expansion vessel pressure and follow ALL the steps you will not be the first to have bought an EV with no pressure in it