Rob is a smooth talking son of a gun. He reiterates what's been said in a finer form. If you bought or were installing said processor you could see for your self that it only has 15mm inlets! Hats off madrab
A poorly designed system can take a while to become evident, as pipe work becomes restricted by sludge etc it can create restrictions. If the vent is just above the water level, as the system heats up it expands the water level in the vent pipe is the same as in the tank, so as it expands it can...
Solutions are.... Fitting an air separator or changing over to a sealed system, if the boiler allows. Both will need a flush of the system. The pump may need replacing too
Your system is pumping over and drawing air in, a badly designed system, you need to look at the feed and expansion connections to the system, possibly the vent pipe does not rise high enough before going back to cistern. If this has been like it for a long time then your system will probably be...
Lol I sound cheeky I know 😝, but what's the size of the incoming main? You can put inch connections on but if it's only a 20mm supply comming in !