I have a Baxi105e and recently it has started making a lound banging noise when either the CH or the DHW makes the boiler fire up. It happens when the water is reaching the thermostat temperature. Ive noticed that the pressure gauge flicks between 1.5 and 2.5 when this happens. Ive been told that its an airlock or the Heat Exchanger?? is clogged up. Ive bled all the radiators and the pump lets out a trickle of water if i loosen the screw on the front. Is there anything i can try apart from finding the money to call someone in. A few years ago i had to change two of the radiator thermostats so im ok with draining the system and removing radiators etc.