Baxi Combi 105e Pressure Varying

We have a Baxi Combi 105e that has been installed for just over a year. Several new radiators have recently been fitted, the system was drained to do this, refilled and all the radiators bled. Everything seemed to work fine, all radiators got hot, no cold spots on radiator, hot water all ok etc. Pressure was steady around 1bar.

Recently a problem occurred where when the boiler does the pre-heat on the hot water the pressure drops considerably, often below 0.5 bar. After the preheat is finished the pressure returns to 1 bar and all is ok. Sometimes the system pressure drops below 1 bar, typically overnight, and then when the pre-heat comes on the pressure drops to 0 bar. If the pre-heat is turned off the problem does not occur. Also sometimes when the system is topped up through the filler loop to 1 bar when the system starts again the pressure goes up to 1.5 bar but stays steady there

Any suggestions on simple things I could check why the pressure drops would be grateful. Thanks in advance.

This all sounds very normal for this model of boiler just top pressure upto just over 1 bar when boiler is cold and all will be well

Thanks for the quick response, much appreciated. We have been topping the boiler up and all has been ok. We were just a little worried that when we do not have time to do this that the boiler gets very noisy when running, would this be causing any damage to pump or anything?