Close coupled central heating?

[soloheadbeg]

Hi
I have a vented CH system consisting of 3 zones - up, down and HW only. Pump is a Groundfos 25 50 and has been operating without issue since at least 1993. The first radiator on both downstairs circuit and upstairs circuit both fill with air within a couple of weeks of bleeding and have done so for years. I’ve tested the gas in both radiators and am confident it is not hydrogen. My pump is on the return pipe about 1m from the boiler. In between the pump and the boiler is the water feed (1/2inch pipe) from f&e tank. My understanding is that this means that my radiators etc are all on the negative pressure side of the circuit and that this might be the reason for the build up of air in the system. The expansion pipe (1inch) is on the flow pipe about 4m from the boiler. I’ll be replacing the pump isolation valves shortly as both are leaking a little and I am wondering if this would be a good opportunity to convert to a close coupled system. If so does the requirement for a max separation of 150mm between the expansion and the feed pipes (both would be placed between boiler and pump on the flow pipe) apply only at the teeing position and can the two pipes follow different paths back up to the f&e tank?
Thanks in advance.

 

[cross thread]

Yes tee off the flow before the pump with no more than 6 inch between the two pipes after that as long as the expansion pipe rises you s be ok

 

[Razor900]

Or just combine the feed and vent if you can...

 

[Johntheo5]

As above, combine the two, my 50 year old system with some rads > 40 years, has the cold feed teed into the vent where it passes up adjacent to the F&E Tank

 

[Justin Passing]

There are 2 pipes
1) Feed and expansion
2) Vent
almost no thermal expansion goes up the vent pipe.

If you combine them, all the pipe must be 22mm min.

 

[Johntheo5]

The vol of thermal expansion taken up by the vent is proportional to the csa of the vent & F&E tank, you don't actually need a vent as long as the cold water feed does not have a isolation valve, fig. 2, below.