Vented v Unvented, Pressurised CH System

[firebladerrw]

Some thoughts and advice please:

Having recently had some CH boiler problems, (now fixed), various engineers have suggested that I should consider an unvented, pressurised system.

I'd like to get some unbiased views on this please:

I currently have a free standing condensing boiler, thats vented and supplied by a tank in my attic. The system does suffer a bit from air, and in winter I've usually got to bleed a couple of the highest radiators twice a month. Not onerous, but a pain nevertheless.

When I had boiler problems, I did consider moving to a Combi boiler, however my experience with them, and in particular shower flow rates hasn't convinced me that is the way to go.

I'm considering moving to a fully pressurised system (via a qualified & certified engineer), by getting rid of the DHW and CH supply tanks in the attic, and also the copper HW tank, replacing it with a stainless steel pressurised storage tank with all the usual pressure regulating valves and expansion vessels etc. Which I'm told will fit in the cupboard where my current HW tank is.

Theory is, I can keep my existing, and relatively simple system condensing grade A boiler, and get cleaner, healthier & pressurised water from the stainless steel tank. Also, as the system is pressurised (and regulated) via the mains, it would hopefully eliminate having to bleed radiators so much.

Thoughts please?

Thanks

 

[stem]

If you want to keep your existing boiler, you will still need to retain the small tank in the attic that feeds it and the radiators. The larger attic feed tank for the hot water can go if you change your existing hot water cylinder for an unvented cylinder.

Changing the hot water part of the system won't do anything to prevent the air in the radiators. Something else will be responsible for that.

Unvented cylinders provide almost mains pressure hot water. So good mains pressure is required, as is a good flow rate, although this is not usually a problem.

Unvented cylinders also need an annual service, to check / recharge the pressure vessel and associated valves, but this can be done at the same time as the boiler, by a suitably qualified engineer. Not all are, because two disciplines are involved.

 

[firebladerrw]

If you want to keep your existing boiler, you will still need to retain the small tank in the attic that feeds it and the radiators. The larger attic feed tank for the hot water can go if you change your existing hot water cylinder for an unvented cylinder.

Changing the hot water part of the system won't do anything to prevent the air in the radiators. Something else will be responsible for that.

Unvented cylinders provide almost mains pressure hot water. So good mains pressure is required, as is a good flow rate, although this is not usually a problem.

Unvented cylinders also need an annual service, to check / recharge the pressure vessel and associated valves, but this can be done at the same time as the boiler, by a suitably qualified engineer. Not all are, because two disciplines are involved.

Thank you.

I understood, perhaps wrongly, that the CH side could also be pressurised (separately from the DHW), using a filling loop with and pressure gauge?

 

[stem]

It can be done, but you would also need a pressure vessel.

Conversions are pretty rare, probably because the cost of doing so outweighs the advantages. However, more common is to wait until the boiler requires replacement and get a system boiler with an internal pressure vessel and filling loop.

If you are seeking to having to stop bleeding the radiators the problem is not down having a feed tank per-se. A properly designed & maintained system with a feed tank won't allow air to be introduced. I have never had to bleed mine in 21 years.

 

[HERTS P&D]

I have never had to bleed mine in 21 years.

That's because the wife does it!

Sorry, made me laugh.

Andy

 

[Mottie]

Had ours converted last year the same as the OP wants. We have a 20 odd year old boiler. We got rid of the cold water storage tank, heating system supply tank and we had an unvented hot water cylinder fitted. Had the system flushed, boiler serviced, two expansion tanks pressure valves and new electronic timer, thermostat and new diverter valves etc. Rads seem much hotter to the touch and there's much, much better pressure from the shower compared to the old gravity system. I have only had to bleed the rads a couple of times since January whereas I was bleeding them every other week. Only problem we had was that within a couple of weeks we had to replace a couple of rads as they sprang a leak due to the higher pressure. They were the last of the original radiators and had been in use since 1961. The boiler had never been serviced since we had it fitted in 1993 and there had been no inhibitor in the system for at least 15 years!

If and when the boiler packs up, we will only need a new heat only boiler and a magnetic filter.