Hi, I'm hoping for some suggestions as to where I go next in my endless mission to stop my system taking on air.
The house has a gravity fed system, 'S' plan, Heat only boiler supplying CH & HW, with separate F&E and vent just before the pump in the typical H layout, pump & valves are all located in the upstairs Airing cupboard.
Boiler and pump have just been replaced as the old boiler was proving unreliable and underpowered for the house (4 Bed, 11 Rads) new Ideal Logic + 24kw installed with Grundfos UPS3 pump. This issue is not new, I have battled with air previous to the boiler and pump replacement and I was hoping this would be solved following the clean, flush and a fresh dose of inhibitor that was done during the work.
So, the problem, once I have all the air out of the system it will run perfect indefinitely, as long as the water is cold!! the air only starts to circulate once the return temperature is in the 50's, as the return temperature rises the air gets worse to the point that the pump will eventually cavitate and stop moving water around the system, this happens on CH, CH+HW and HW only, the air is however much worse on HW only as the return temp is a lot higher especially towards the end as the cylinder approaches set temp (60 Deg). Again on CH only it only slightly makes a small amount of air as the return is around 50 Deg.
I added some further x100 as I had 50% emptied a rad a few times (air gets trapped in the rad return line) and this has made no difference to the issue, I have tried the pump on all speed settings and this makes no difference, I tried the glass of water on the vent line and all seemed good (water dropped about an inch when the pump turned on and came back up within a few seconds) header tank level slightly drops on pump turn on so looks OK.
Checked all the accessible unions on the valves, Pump, HW Balance valve and looked over everything, no evidence of leaks. I even checked the return line at the boiler with the heating on and definitely had positive pressure as the filter could still be bled (Mag filter above boiler on return line) so no sucking in of air.
I am all out of ideas, other than corrosion somewhere in the return line, is that possible and will it make air so quickly? After I have bled the system the pump will cavitate after 5 mins once the return is into the 55-60 deg region.
Currently I can keep the system going but reducing the boiler output temp to around 62, this keeps the return on CH well below 50, I start to build air when HW only on demanded but not enough to cavitate the pump, only downside is the HW takes an age to recover and the boiler short cycles as its minimum output is too much for the small temperature difference.
Any ideas or suggestions would really help, as I mentioned above I can leave the system running for hours with the boiler temp set to minimum so cannot get my head round this being a leak.
The house has a gravity fed system, 'S' plan, Heat only boiler supplying CH & HW, with separate F&E and vent just before the pump in the typical H layout, pump & valves are all located in the upstairs Airing cupboard.
Boiler and pump have just been replaced as the old boiler was proving unreliable and underpowered for the house (4 Bed, 11 Rads) new Ideal Logic + 24kw installed with Grundfos UPS3 pump. This issue is not new, I have battled with air previous to the boiler and pump replacement and I was hoping this would be solved following the clean, flush and a fresh dose of inhibitor that was done during the work.
So, the problem, once I have all the air out of the system it will run perfect indefinitely, as long as the water is cold!! the air only starts to circulate once the return temperature is in the 50's, as the return temperature rises the air gets worse to the point that the pump will eventually cavitate and stop moving water around the system, this happens on CH, CH+HW and HW only, the air is however much worse on HW only as the return temp is a lot higher especially towards the end as the cylinder approaches set temp (60 Deg). Again on CH only it only slightly makes a small amount of air as the return is around 50 Deg.
I added some further x100 as I had 50% emptied a rad a few times (air gets trapped in the rad return line) and this has made no difference to the issue, I have tried the pump on all speed settings and this makes no difference, I tried the glass of water on the vent line and all seemed good (water dropped about an inch when the pump turned on and came back up within a few seconds) header tank level slightly drops on pump turn on so looks OK.
Checked all the accessible unions on the valves, Pump, HW Balance valve and looked over everything, no evidence of leaks. I even checked the return line at the boiler with the heating on and definitely had positive pressure as the filter could still be bled (Mag filter above boiler on return line) so no sucking in of air.
I am all out of ideas, other than corrosion somewhere in the return line, is that possible and will it make air so quickly? After I have bled the system the pump will cavitate after 5 mins once the return is into the 55-60 deg region.
Currently I can keep the system going but reducing the boiler output temp to around 62, this keeps the return on CH well below 50, I start to build air when HW only on demanded but not enough to cavitate the pump, only downside is the HW takes an age to recover and the boiler short cycles as its minimum output is too much for the small temperature difference.
Any ideas or suggestions would really help, as I mentioned above I can leave the system running for hours with the boiler temp set to minimum so cannot get my head round this being a leak.