Baxi Combi 105 HE pressure over 3 bar

[redtop]

Hi, can anyone help i have problem with varying pressure for the CH on my baxi 105he. It goes above 3 bar and the PRV lifts and hot water dribbles outside through a vent. When the boiler is shutdown and allowed to cool the pressure can drop below 1 bar (to about 0.6) I have tried to re pressure to around 1 to 1 .25bar with success but as soon as the boiler is used again the pressure goesback up above 3 and it vents again via the PRV. Could it be the pressure bladder? I've read in the FAQ and it mentions checking the pressure. The only problem is I m not sure what the pressure should be set to. Does anyone have any recommendations. note (The filling loop is dissconnected so no interference with the above symptoms) Thanks In advance

 

[Lusi83]

Hi not an expert - but that's what mine does (different model/make) - and it needs a new expansion vessel/tank....(or the expansion vessel being pumped up but I'm ghaving a new one )
HTH

 

[45yearsagasman]

Recharge (pump up) the EV to between .75-1bar. This must be done with no pressure in the system. No water should come from the schraeder valve. Refill the system to 1 bar and give it a try.
There are other reasons why the pressure rises abnormally:-
1 The communication tube to the EV is blocked (rare on this model)
2 The plate heat exch may have failed internally, and cold water is crossing to the primary side.

 

[redtop]

thanks for the replies, I did get round to checking the pressure in the EV and it was flat/zero! I pumped it up to 1 bar (with the central heating circuit flat) and now its alot better, though the pressure can get up to 2.7/2.8 bar when radiators are on full and the hot water in use. According to the manufacturers instructions it should be 2.5 at the highest. It is definately better though and the PRV has not lifted since.

 

[newbuildinstaller]

thanks for the replies, I did get round to checking the pressure in the EV and it was flat/zero! I pumped it up to 1 bar (with the central heating circuit flat) and now its alot better, though the pressure can get up to 2.7/2.8 bar when radiators are on full and the hot water in use. According to the manufacturers instructions it should be 2.5 at the highest. It is definately better though and the PRV has not lifted since.

You may need an extra expansion vessel as the water volume in your system maybe more than your current EV can handle (12% of total system water content) you an add a external EV anywhere you can hide it out of the way.

REMEMBER you cannot oversize a expansion vessel but you can undersize

 

[newbuildinstaller]

thanks for the replies, I did get round to checking the pressure in the EV and it was flat/zero! I pumped it up to 1 bar (with the central heating circuit flat) and now its alot better, though the pressure can get up to 2.7/2.8 bar when radiators are on full and the hot water in use. According to the manufacturers instructions it should be 2.5 at the highest. It is definately better though and the PRV has not lifted since.

You may need an extra expansion vessel as the water volume in your system maybe more than your current EV can handle (12% of total system water content) you an add a external EV anywhere you can hide it out of the way.

REMEMBER you cannot oversize a expansion vessel but you can undersize

 

[newbuildinstaller]

thanks for the replies, I did get round to checking the pressure in the EV and it was flat/zero! I pumped it up to 1 bar (with the central heating circuit flat) and now its alot better, though the pressure can get up to 2.7/2.8 bar when radiators are on full and the hot water in use. According to the manufacturers instructions it should be 2.5 at the highest. It is definately better though and the PRV has not lifted since.

You may need an extra expansion vessel as the water volume in your system maybe more than your current EV can handle (12% of total system water content) you an add a external EV anywhere you can hide it out of the way.

REMEMBER you cannot oversize a expansion vessel but you can undersize