Heating design - underground pipes with external boiler

[bonehill]

Looking at where to place an external boiler, and some guidance on best practice is needed!

Very conventional system - heat-only oil boiler, fully pumped, Y plan, indirect cylinder, F&E tank, 7 rads, all in a 2 bed cottage. It's a spring-supplied system, not on mains, so there is only 0.5 bar from main cold tank in loft, hence no combi etc.

Placing the boiler right up against the wall at ground level is tricky, there's only a narrow path. Best location is in the garden where the ground is about 2ft higher.

So, feed and return would go underground from the boiler, down more than 2ft to below the path - this is lowest point. Would then rise into house, up to cylinder on 1st floor etc.

One engineer quoting has said that I'm going to get airlocks - that the flow leaving the boiler needs to rise all the way to the f&e tank. Is this accurate? Can I only drop underground if it's a pressurised system?
I know airlocks would be a risk if I had it going up and down multiple times, but it would only have one low point, under the path, so any air in the system would either rise to the f&e, or to the boiler itself.

Digging in the insulated pipes is a hassle, but it's a lot less than re-landscaping half the garden and access, so any guidance on how I can make this work?

Thanks in advance

 

[bernardgreen]

The layout of my cottage needed a similar pipe layout. The boiler is in the single story kitchen ( an extension ) . Flow and return pipes go up from the boiler and then drop to ground level under the boiler, they then run horizontally at ground level into the main cottage. Then they go upwards to the first floor where there is a hot water cylinder and the F&E tank. Ground floor radiators supplied by drops from the first floor

Automatic air release valves on the high points of the flow and return above the boiler keep the system air free. 9 years so far and no problems