well well well....I contacted my highly recommended heating engineer (not going to say who he works for but they happen to make said boiler! ) who confirmed that a tiger loop was indeed not recommended for HRM wallstar but I managed to convince him to install one.....and, at a stroke ALL the air bubble problems have gone !!!
There are still micro bubbles coming in from the supply pipe (I specifically requested he use clear oil lines) probably due to the vacuum caused by lifting the oil and if you tap the fire valve it also produces a stream of bubbles (yes, I have replaced it with a quality Valspar one and every connection throughout is sealed with Heldite) but after a second or so they arrive at the tiger loop and are quickly separated from the oil
The boiler also shuts down pretty much instantly and certainly more quietly which confirms that no air is getting to the injector
thanks to all who persevered in recommending its' fitment
There are still micro bubbles coming in from the supply pipe (I specifically requested he use clear oil lines) probably due to the vacuum caused by lifting the oil and if you tap the fire valve it also produces a stream of bubbles (yes, I have replaced it with a quality Valspar one and every connection throughout is sealed with Heldite) but after a second or so they arrive at the tiger loop and are quickly separated from the oil
The boiler also shuts down pretty much instantly and certainly more quietly which confirms that no air is getting to the injector
thanks to all who persevered in recommending its' fitment