Saunier Duval Pressure Prob!

[muckylugs]

I have a saunier duval combi, the problem is that if i fill it to 1.5 bar as specified i cannot set the temp to full output as this then send it over the 3 bar max resulting in the pressure valve operating.At the moment i have the pressure set at 1 bar and the temp at about 3/4 full and the pressure is right on the 3 bar limit.
does anyone know what could be causing the extra pressure, i have bled the radiators and there does not seem to be any air in the system
thanks for any help in advance

 

[kevplumb]

do a search on repressurising expansion vessel