Hi again Ric2013. As the 2 offending/cold loft rads have NO air in them (only water comes out when I bleed them) I must assume the air lock is somewhere between the 1st rad on the loft circuit (as this has always worked) and the two others. The pic I posted earlier showing the 90degree elbows taking first floor (copper pipework) into plastic pipe that feeds the 3 loft rads. From the plastic elbows to the first rad (that working one) is about a 5m straight & level run. From this rad to the next rad (which is the first cold one but full of water) is another straight and level 3m run. I'm surprised how the air can always get trapped somewhere on this section and not say in the 90 elbow area. Will an air vent (auto or manual) in the only accessible area (below the 90degree elbows shown on pic) solve this if the air lock is elsewhere along the run ie. over 5m away? Can this air just come from elsewhere in the heating system and migrate up into loft and just happen to always want to 'settle' in this particular area of pipe run?
One other qu. that might be relevant to our loft airlock? We have a tall Bisque rad similar to this
TRB-180-30 - Trubi radiator range - General Radiators
in a first floor bathroom. It's 1800mm tall. It makes a waterfall/running water sound which I understand from Bisque tech people is quite common for these tall rads (so much so that they have a specific tech sheet they send to help customers bleed these style of rads). I can get the air out by way of this convoluted process each year but neverteheless it does eventually start the running water noise a few weeks after having been bled. So might this one bathroom rad on the first floor (which used to be the highest point in the system) be generating air just because of its design and it's this air that's now seeing a higher point to travel to ie. Our loft?
One other qu. that might be relevant to our loft airlock? We have a tall Bisque rad similar to this
TRB-180-30 - Trubi radiator range - General Radiators
in a first floor bathroom. It's 1800mm tall. It makes a waterfall/running water sound which I understand from Bisque tech people is quite common for these tall rads (so much so that they have a specific tech sheet they send to help customers bleed these style of rads). I can get the air out by way of this convoluted process each year but neverteheless it does eventually start the running water noise a few weeks after having been bled. So might this one bathroom rad on the first floor (which used to be the highest point in the system) be generating air just because of its design and it's this air that's now seeing a higher point to travel to ie. Our loft?