O
Oldwoody
Hello there
We have installed a boiler stove (TF70) using all 4 tappings and returns corss flowed. I have no issues with the pumped side to CH, but I intermittently have issues with the gravity supply to the cylinder coil. It's all done in 28mm but it is a long run (about 30foot) with a good few 90's here and there to snake it's way through various obstructions. Although it rises all the way the majority of the run is rising slowly.
The issue seems to be airlocking, particularly when someone uses a lot of water out of the cylinder whilst the system is up to full temp - i.e. full cylinder, rads on. When the stat (fitted on return) senses the drop in temp it turns off the pump and the gravity system should take over. However in most cases it seems to fail. The flow to the cylinder gets very hot, the stove starts to kettle. The return pipe stays cold. The return stat is set to 45C.
As an intermediate solution I fitted a stat to the flow, and set it to about 75C. The effect here was to switch on the pump and avoid the boil. When the pump comes on I can hear air clearing from around the coil area and venting up the vent pipe. So I am convinced it is an airlock created by the gravity circuit.
Has anyone got any ideas why the air is being trapped in the gravity circuit, and not going up the vent? The highest point of the gravity circuit is the swept tee off the flow where the 22mm vent is perfectly vertical. The flow from this tee goes horizontal for about 6 inches, then drops 6 inches via an elbow, then into the cylinder via another elbow. The return out of the cylinder actually rises about an inch (to avoid some other pipework) before joining on to the return pipework and the feed pipe from F&E tank in the loft. This is the same swept tee configuration (28/22/28).
The gravity rad has not been connected yet. A Tee off the 22mm vent (about 6 inches up from the swept tee to cylinder) and one on the return have been left with gate valves ready to connect up. I am tempted to fit an AAV on the pipe to the gravity rad but this seems like a workaround and not a solution. Even if I did not fit the AAV would air “travel” to the gravity rad rather than the cylinder coil? The highest point on the gravity rad is higher than the cylinder coil.
I would really appreciate any input on this you may have, or any similar experiences. I will get a picture taken, as I know it would be much easier to understand!
We have installed a boiler stove (TF70) using all 4 tappings and returns corss flowed. I have no issues with the pumped side to CH, but I intermittently have issues with the gravity supply to the cylinder coil. It's all done in 28mm but it is a long run (about 30foot) with a good few 90's here and there to snake it's way through various obstructions. Although it rises all the way the majority of the run is rising slowly.
The issue seems to be airlocking, particularly when someone uses a lot of water out of the cylinder whilst the system is up to full temp - i.e. full cylinder, rads on. When the stat (fitted on return) senses the drop in temp it turns off the pump and the gravity system should take over. However in most cases it seems to fail. The flow to the cylinder gets very hot, the stove starts to kettle. The return pipe stays cold. The return stat is set to 45C.
As an intermediate solution I fitted a stat to the flow, and set it to about 75C. The effect here was to switch on the pump and avoid the boil. When the pump comes on I can hear air clearing from around the coil area and venting up the vent pipe. So I am convinced it is an airlock created by the gravity circuit.
Has anyone got any ideas why the air is being trapped in the gravity circuit, and not going up the vent? The highest point of the gravity circuit is the swept tee off the flow where the 22mm vent is perfectly vertical. The flow from this tee goes horizontal for about 6 inches, then drops 6 inches via an elbow, then into the cylinder via another elbow. The return out of the cylinder actually rises about an inch (to avoid some other pipework) before joining on to the return pipework and the feed pipe from F&E tank in the loft. This is the same swept tee configuration (28/22/28).
The gravity rad has not been connected yet. A Tee off the 22mm vent (about 6 inches up from the swept tee to cylinder) and one on the return have been left with gate valves ready to connect up. I am tempted to fit an AAV on the pipe to the gravity rad but this seems like a workaround and not a solution. Even if I did not fit the AAV would air “travel” to the gravity rad rather than the cylinder coil? The highest point on the gravity rad is higher than the cylinder coil.
I would really appreciate any input on this you may have, or any similar experiences. I will get a picture taken, as I know it would be much easier to understand!
