CH vent pipe problems - new Y-plan setup

[anta]

I've just converted our old C-plan into a Y-plan setup. Originally the tank feed and the vent connections went either side of the HW cylinder coil between it and the boiler. The feed on the upper pipe (from boiler to cylinder) and the vent on the return.

In my all new Y-plan I've not moved the feed and vent, and now when the HW is on the pump sends water up the vent pipe. Basically there are two loops - one through the HW cylinder coil, and another via the vent pipe, loft tank, and down the feed. This means we have a plastic tank of steaming water in the loft! Not good me thinks!

I was thinking of moving the vent to be just before the pump, but then I guess it might suck in air. There isn't a lot of head as it's a bungalow.

Where shoud the feed and vent pipes attach?

 

[TicklyT]

I believe it's usual practise to have the both feed and vent adjacent to each other, usually both teed into the flow pipe, no more than about 6" apart, just before the pump. Then there's little or no pressure differential between the two.

 

[anta]

OK - that would make sense, except that the vent won't be connected to the highest point in the system. Is that a problem?

The pump is vertical pumping upwards into the bottom of the valve. The valve then splits left and right, and that's the highest point of the whole circuit.

Can I just join the feed and vent into the same place? To equalise the pressure? That's an easy fix for me to do too. Too easy?

 

[spikebmth]

no problem if vent not on highest point. you;ll need to put a manual air vent on the old open vent postition.

The new open vent should be connected before the new cold feed within 6", and before the pump.

so order on flow pipe is boiler, open vent, cold feed, pump, 3 port valve

 

[anta]

OK, but doesn't that mean that there's part of the system which won't ever self bleed?

 

[spikebmth]

you are correct, but a system shouldn't need bleeding at all, if running correctly. you can vent when you fill, from manual vent on the high hot water flow pipe.

 

[twgas]

That part of the system that won't self bleed will need either a manual or automatic vent, obviously the auto-vent will self bleed (until it leaks).
Sounds to me as though you have the pump and valve(s) before the vent - totally wrong and potentially dangerous.

 

[anta]

I'd only just converted to a y-plan, and the vent and feed were either side of the cylinder coil - vent at the highest point and feed between coil and boiler. In the old setup it wasn't a problem as the coil was convected flow so no pressure on that circuit.

Anyhow, thanks to you guys it's now fixed. Boiler -> vent -> feed -> pump. All bled and working fine, no water cycling at the loft tank! The vent pipe does get quite hot now as the hottest water in the system flows under it and convects up the pipe. I guess that's not a problem though as it doesn't actually flow out of the top.