Hi everyone.
I have a very old central heating system which has been repeatedly modified since inception in the early 60's. We have a Crane Cavalier cast iron boiler (modified to natural gas!) on the ground floor which still works very well, although with some kettleing. Some demented heating engineer in the past tried to get gravity feed into the ground floor with a single pipe system using many very fat pipes up to 44mm. In the end a pump was added at ground level. Some of the fat pipes have been stripped out and replaced with two-pipe 15mm to serve the ground floor heating. The first floor heating was always two-pipe, as far as I can tell.
There was originally a Primatic DHW cylinder. This has been replaced some time ago with an insulated indirect cylinder, which had the insulation cut off and then glued back on, in order to get it into the cupboard. There is therefore no longer access to the connections, without again cutting off the insulation and removing the tank. A F&E tank is mounted above the cylinder in the loft space, installed when the Primatic cylinder was replaced.
Feed from the boiler in 22mm pipe connects to the bottom coil connection, and then proceeds up to the vent which has about 400mm above the water level in the F&E, which is as high as it can get because of the roof. F&E connects in 22mm to the upper coil connection and then down to pump inlet thence to the boiler return. Other returns from the heating join it at intervals.
You will all have noticed the first problem is that the cylinder is connected the wrong way round. That doesn't worry me overmuch, as we still get hot water with gravity circulation, now that I've flushed out the coil in the cylinder, and chemically cleaned the system. Steam from the boiler would still go straight to the vent, past the lower cylinder connection.
My main problem now is that since cleaning, the system over pumps a consistent trickle with the pump set at it's lowest setting. I'm considering a cure using the scheme set out by ChrisR in post here: //www.diynot.com/forums/viewtopic.php?p=341459#341459
If I connect the feed into the vent pipe, and put an automatic air vent on the top of the pipe that used to go to the top of the coil, above the cylinder, would that work OK please? Or should I use a manual vent?
Thanks for any suggestions.
I have a very old central heating system which has been repeatedly modified since inception in the early 60's. We have a Crane Cavalier cast iron boiler (modified to natural gas!) on the ground floor which still works very well, although with some kettleing. Some demented heating engineer in the past tried to get gravity feed into the ground floor with a single pipe system using many very fat pipes up to 44mm. In the end a pump was added at ground level. Some of the fat pipes have been stripped out and replaced with two-pipe 15mm to serve the ground floor heating. The first floor heating was always two-pipe, as far as I can tell.
There was originally a Primatic DHW cylinder. This has been replaced some time ago with an insulated indirect cylinder, which had the insulation cut off and then glued back on, in order to get it into the cupboard. There is therefore no longer access to the connections, without again cutting off the insulation and removing the tank. A F&E tank is mounted above the cylinder in the loft space, installed when the Primatic cylinder was replaced.
Feed from the boiler in 22mm pipe connects to the bottom coil connection, and then proceeds up to the vent which has about 400mm above the water level in the F&E, which is as high as it can get because of the roof. F&E connects in 22mm to the upper coil connection and then down to pump inlet thence to the boiler return. Other returns from the heating join it at intervals.
You will all have noticed the first problem is that the cylinder is connected the wrong way round. That doesn't worry me overmuch, as we still get hot water with gravity circulation, now that I've flushed out the coil in the cylinder, and chemically cleaned the system. Steam from the boiler would still go straight to the vent, past the lower cylinder connection.
My main problem now is that since cleaning, the system over pumps a consistent trickle with the pump set at it's lowest setting. I'm considering a cure using the scheme set out by ChrisR in post here: //www.diynot.com/forums/viewtopic.php?p=341459#341459
If I connect the feed into the vent pipe, and put an automatic air vent on the top of the pipe that used to go to the top of the coil, above the cylinder, would that work OK please? Or should I use a manual vent?
Thanks for any suggestions.
The outcome of this, and tested by breaking the circuit and pouring water down a pipe to see where it emerged, is that the flow DOES connect to the top of the coil, not the bottom, and that pipe continues as the vent pipe. It was therefore simple and conventional to connect the fill pipe into that, above the cylinder, and terminate the lower connection pipe with a manual bleed valve, also just above the cylinder. 
