combined feed and vent

[freecountry65]

I need to move the feed and expansion tank of my vented system to a position above a new loft extension. The space is basically tiny and won't allow the 400mm needed for the expansion pipe above the tank. I've heard of combining the f and e which would seem to be a solution. However the pipe would have to have a horizontal section in it (about 800mm) to get it to the new tank position. Would this invite airlocks?
Also can it be done in plastic?
Any other tips appreciated.
thanks.

 

[45yearsagasman]

You can only make those alterations if your boiler has overheat protection and the manufacturer allows it. Horizontal pipe on a 22mm feed and vent is asking for trouble during refilling.

 

[Hufty]

Can you convert your system to a sealed system (depends on boiler - look in the installation instructions) in which case no need for the header tank.

Rather than any concerns about how long it takes the plumber to fill the system, I thought the issue with a combined f&e pipe is the risk of it getting blocked, which would mean no way of venting the pressure build up that would happen when the boiler heats the water. This is why you're unlikely to find a manufacturer allowing it.

Personally I wouldn't want to convert a safe system into a less safe system, but I guess you might add a PRV somewhere in a combined f&e system for peace of mind.