Converting to sealed CH, parts question

[Tom Pickles]

After advice here about CH issues, which appear to be cavitation, I am look ing into changing my system from open vent to sealed. I have checked my boi ler (Micron 50FF) has an overheat stat, and it's all looking good to move f orward.

I've a header tank in the loft, which I'll swap out with an expansion vesse l and safety relief valve. I'll utilise the existing hole in the fascia boa rd where the overflow exits, with 15mm copper, to vent if/when pressure get 's too high and the safety valve dumps.

Can you buy a pressure gauge that I can plumb in the airing cupboard? I hav e looked around the net, but all the pressure gauges appear to come as part of a kit, or with just a threaded connection, which I assume screws into a manifold.

What do I need to plumb a lone pressure gauge in?

Thanks!

[John Rumm]

You can get complete kits that include the filling loop, connection to the expansion vessel and the pressure gauge, and over pressure blow off valve, e.g. :

(or something like BES part number 20244 which includes the expansion vessel as well)

Yup, many will have

Most have a 1/2" BSP threaded connection - some male some female. You just need a suitable connector to go from that to a 15mm pipe fitting of some sort. Some will need to seal on the threads - others may have an O ring or flange for a washer.

[Andrew Gabriel]

Blow off pipe isn't allowed to pour super-heated water over passers-by ;-) It's normally angled back to direct the water at a brick wall. You can get specially made terminals to do that. It's probably best connected near the boiler flow/outlet. I would strip all the plumbing out of the loft. If left there and pressurised, it's just something waiting to freeze and leak one day.

Pressure vessel should ideally be connected to the system as near to the pump inlet as is reasonably possible. The nearer, the less cavitation you get due to pressure changes at pump inlet.

Filling loop and pressure guage need to be in the same place, so you can read the guage whilst filling and topping up the system.

The increased pressure in the system may reveal some leaks you didn't know you had. I wouldn't waste a bottle of inhibitor which you might well need to drain off to fix a leak somewhere for first couple of days.

[Tom Pickles]

looking into changing my system from open vent to sealed. I have checked my boiler (Micron 50FF) has an overheat stat, and it's all looking good to mo ve forward.

essel and safety relief valve. I'll utilise the existing hole in the fascia board where the overflow exits, with 15mm copper, to vent if/when pressure get's too high and the safety valve dumps.

My solution isn't ideal I know, but it will be vented from the fascia on a two storey house, overlooking the back garden. Just me and wife, so low ris k. The valve should only dump if there's a problem, and I'm going to over-s ize the expansion vessel to keep the pressure increase minimal in the syste m.

I'll get it repositioned when we finally get the boiler replaced.

We never had any issues with freezing pipes in the loft, even in that reall y bad winter, 2011 was it?

There's no space in the airing cupboard near the pump to put the vessel, so it will have to go in loft, about 4' pipe length away. It will be on the i nlet side though.

Good point, thanks.

[Andrew Gabriel]

The dangerous pressure comes from the water boiling if the boiler goes wrong, and what's ejected is super-heated water (well above 100C) and steam. Expansion vessel has nothing to do with it.

Another thing, you need to go through the boiler installation instructions, and make sure your modified system matches its installation requirements for a sealed system.