Persistent air problem in hot water/heating (mainly the hot water)
About 8 weeks ago I put new TRVs on the radiators, fitted a bypass valve and replaced a 28 year old grundfos pump with a new grundfos Alpha+. This system is a vented gas central heating type with a header tank approx 2m above the pump. The system was completely drained, radiators removed and flushed and everything re-filled including using rust inhibitor. (The ABV was set at 3, I admit I've still to re-balance all the radiators).
I seem to have a lot of air in the system. It is noisy when only the hot water is on, even with pump set to speed '1'. On variable or higher speed it is worse. With the central heating in use the system goes much quieter and is fine. All radiators have been vented a couple of times and air was released.
I mounted the pump with the motor spindle horizontal - as recommended The flow too is horizontal, in same direction as the old one which is towards the 'Y' valve and the top of the hot water cylinder. Immediately before the pump (about 4 inches from the pump inlet) the vent pipe rises into the loft. I suspect there was still air in the heating after the previous work. But why is it so pronounced when just the hot water heating is on. I'm wondering if the 'better' pump is sucking air in from the vent pipe - I guess this might be possible.
I checked the header tank and noticed air bubbles coming from the cold water pipe which feeds down into the system. I could also feel the flow from that pipe - sometimes pushing water in, sometimes sucking. I tried putting the vent pipe, which is above the water level in the header tank, in a jug of water. Then turning on the system (hot water only) resulted in the water being sucked into the pipe. However this may be normal.
Would turning the pump around make sense? pushing towards the vent? Is there some other tip to fix this. Is it because there is air still in the system that allows some compression of the air and therefore instability?
Incidentally the cold water feed goes into the system about 12" away from the bottom of the hot water cylinder. The pump pushing towards it.
About 8 weeks ago I put new TRVs on the radiators, fitted a bypass valve and replaced a 28 year old grundfos pump with a new grundfos Alpha+. This system is a vented gas central heating type with a header tank approx 2m above the pump. The system was completely drained, radiators removed and flushed and everything re-filled including using rust inhibitor. (The ABV was set at 3, I admit I've still to re-balance all the radiators).
I seem to have a lot of air in the system. It is noisy when only the hot water is on, even with pump set to speed '1'. On variable or higher speed it is worse. With the central heating in use the system goes much quieter and is fine. All radiators have been vented a couple of times and air was released.
I mounted the pump with the motor spindle horizontal - as recommended The flow too is horizontal, in same direction as the old one which is towards the 'Y' valve and the top of the hot water cylinder. Immediately before the pump (about 4 inches from the pump inlet) the vent pipe rises into the loft. I suspect there was still air in the heating after the previous work. But why is it so pronounced when just the hot water heating is on. I'm wondering if the 'better' pump is sucking air in from the vent pipe - I guess this might be possible.
I checked the header tank and noticed air bubbles coming from the cold water pipe which feeds down into the system. I could also feel the flow from that pipe - sometimes pushing water in, sometimes sucking. I tried putting the vent pipe, which is above the water level in the header tank, in a jug of water. Then turning on the system (hot water only) resulted in the water being sucked into the pipe. However this may be normal.
Would turning the pump around make sense? pushing towards the vent? Is there some other tip to fix this. Is it because there is air still in the system that allows some compression of the air and therefore instability?
Incidentally the cold water feed goes into the system about 12" away from the bottom of the hot water cylinder. The pump pushing towards it.
