Converting to sealed CH

[Jon]

Hi all,

After cleaning, flushing rads and pipework, installing a new Grundfos Alpha2 pump, a programmable room stat and more TRV's, I was thinking of converting to a sealed system from open vented in my 8yr old house to continue with the modernisation of the system.

The boiler is a GW Micron 50FF, which I have confirmed will be ok with a pressurised system. I have a couple of queries though and would appreciate some confirmation or correction. I have read Ed's sealed CH FAQ.

I was thinking of replacing the feed/expansion tank in the loft with the expansion vessel, feed loop and pressure valve and discharge, using the existing pipework there as there is no room in the airing cupboard for the vessel. Connecting the expansion vessel to the vent pipe and connecting the mains water feed from the tank to the water inlet via the filling loop. This will end up with the expansion vessel being plumbed before the pump. Is this all ok ??

Can I use the overflow pipe from the F/E tank to connect to the pressure relief valve as a discharge pipe? It's plastic and teminates outside via the fascia board (two storey house) overlooking our back garden.

Twelve rads and the boiler, calculating approx 10 litres for each, I scoped a 18 litre expansion vessle which would give a nice tolerance over the required capacity.

I also have one of those Aerjec things in place:

understand this will likely be defunct in a sealed system. Can I leave this in place or should I take it out and plumb the pipes back together?

Thanks,

Jon

[Dave Plowman (News)]

My opinion is it's not worth it. It might be if you needed the position taken by the header tank. When you do come to replace the boiler you might - as I did - decide on a system one, and that includes the pressure vessel.

[David Hansen]

On Fri, 28 Nov 2008 03:41:57 -0800 (PST) someone who may be Jon wrote this:-

Is converting a heating system to "unvented" a modernisation?

[Roger Mills]

I considered doing something very similar with my system, but decided in the end to wait until such time as the boiler has to be replaced.

I think what you're suggesting should work, though I'm not sure about the plastic overflow - the water discharged by the pressure relief valve could potentially be pretty hot!

One thing which put me off is that, although my boiler (Baxi Solo PF MkI) is suitable for use in an unvented system, the installation manual says that the relief valve should be "close to the boiler" - which it certainly wouldn't be in my case if mounted in the roof space above the airing cupboard.

Another consideration was the fact that my roof has a fairly low pitch (about 30 degrees) and the F&E tank is mounted in the eaves with very little headroom. Although I could probably install the expansion vessel in its place, I'm not sure that I fancy having to grovel in there at a later date for maintenance work such as checking/re-charging the air pressure - or even for operating the filling loop.

[Jon]

Thanks for your replies guys. Maybe I'll take your advice and leave it until the boiler packs up.

[Ed Sirett]

I would mount the expansion vessel on the feed pipe in the loft. I would mount the releif valve near and outside wall (do not use the plastic pipe for a discharge pipe, it may well never be needed, but it may one day have to discharge steam). I would mount the filling loop in the airing cupboard, with a pressure gauge nearby. You can leave the Aerjec in situ. I'd chop back to near the top of the Aerjec and put a manual (or auto) bleed/vent unit on it.

As others have said if the existing system is not drawing in air or pumping over there is little to be gained.