Gas boiler choice: aluminium vs. stainless steel heat exchanger

I am thinking about having my old, inefficient but reliable gas boiler replaced next summer. I have been reading manuals and other web resources, mainly looking at German and Dutch manufacturers.
The review of the Giannoni stainless steel heat exchanger at <www.gas-news.co.uk/archive/storage/pre-10/2007/comment/1006.htm> does not fill me with confidence -- too much plastic, and no way to strip it down to clean it.
On the other hand, cleaning the Worcester WB3 aluminium heat exchanger at <www.gas-news.co.uk/archive/storage/2008/comment/1001.htm> seems labour intensive, particularly if it is needed every year.
I have been looking at the Dutch company Remeha (Broag, their UK importers, are just down the road). I believe the Avanta has a Giannoni heat exchanger, while the Quinta has a cast aluminium heat exchanger.
I prefer the look of the Quinta -- it seems more solidly built and accepts an external 0-10v modulating input if I wanted to update the system controls later. However, I am wary of the aluminium heat exchanger.
Now that condensing boilers have been around for a few years, what are people's experience with the relative life and cost of maintenance of aluminium vs. stainless steel?
Regards,
MJA
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The Quinta is a commercail boiler, so more expensive. At this point consider a system update. How about a quality high flow combi, giving high pressure showers? The Broag 39C combi will do in most cases.
Have a Magnaclean on the return to the boiler. That will prevent any blocking up of the tubes in the heat exchanger.
The Broag, has a 5 year guarantee. They use primarily industry standard components and little plastic with Honeywell brass hydrobocks. The Broags are better quality than Vaillant and much cheaper. They are a well priced quality boilers having a superb control system with integrated outside weather compensation and OpenTherm control protocal control. http://www.avantaplus.co.uk
http://www.tradingdepot.co.uk/DEF/catalogue/D003001007/Plumbing/Central%20Heating/Central%20Heating%20Boilers/Broag%20Remeha%20Boilers
The control options. Wiring the combis is simple: http://www.avantaplus.com/docs/Issue%205%20-Avanta%20Schematics%20Booklet.pdf
Go for the Avantaplus range.
Now what is your system like? Cylinder? vented? how many showers? Baths, etc. Then it can be whittled down to what you really need. It is no good putting a modern boiler on an outdated DHW/CH system. Go for gold.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

We've had a few water outages in my part of the Thames Valley, and I also like having the backup immersion heater. Space for tanks is no problem.

The Magnaclean is worth considering -- although the system seems fairly clean and has had inhibitor in.

Yes, I have looked at the Avanta and Quinta instructions. I am wary of OpenTherm because the interface specs are not published -- same problem for Vaillant and eBus. A standard 0-10v input seems future proof -- that limits me to the Quinta 30, Keston Qudos or MHG with option module.

Current system original when 3 bed bungalow built in mid 1970's. Gas boiler Potterton C55 cast iron, floor standing, conventional flue, 55,000 Btu output, which is adequate given the insulation improvements since the bungalow was built. Conventional hot water system -- indirect tank in airing cupboard, primary gravity circulation, open vent with Honeywell "C" system added by previous owner. One bathroom, bath with gravity fed shower over. One-pipe pumped central heating circuit, hall thermostat added by previous owner.
The economics of an upgrade are finely balanced. Current running costs are about 700 pounds fuel, plus 60 pound annual boiler service. A new boiler could be cost neutral over 10 years assuming a fuel saving of 250 pounds per year and 2500 for new boiler, installation and essential system changes. Higher maintenance costs would put me off the change, higher gas prices could make it worthwhile.
The old boiler is supremely reliable, and I would hate to find I had swapped it for something as unreliable as the Worcester Firefly HD II my father had years ago -- the flame sensor probe positioning was critical so it regularly locked out leaving us to return to a cold house, and it burnt through glow-plugs every few months.
I asked about stainless steel versus aluminium as the boiler choice FAQ at www.makewrite.demon.co.uk/BoilerChoice.html views aluminium as questionable, even though many manufacturers use it (Remeha Quinta, Buderus, Worcester, etc.). The boiler choice FAQ mentions one incident of aluminium corroding on the water side -- is this a problem nowadays with correct inhibitors?
Regards,
MJA
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The Magnaclean is essential on a Gianonni heat exchanger and on any system.

The Avantaplus system boiler is a "Dual Temperature" boiler. High temp to re-heat DHW and resorts to weather compensation after. An external 3-way valve is controlled by the boiler for this.
How long were water outages? These are usually not very long, so are you over exaggerating? You can keep the tank and supply the toilets only with this so it gives toilet backup in case of a failure. An in-line instant electric water heater in the combi outlet gives backup and can do the shower and one tap until the combi is backup. Get you wet enough. About 100-110. This is a small box that can go in the loft
The one-pipe system may be a problem on most boilers. A restricting gate valve usually solves it, as the pumps are too fast and pump past the rads. Many installer will not touch them and insist on ripping it out and putting in a two-pipe system.
I would go for a Broag 35C or 39C combi that gives powerful showers and no pumps and get rid of the cylinder (on its last legs after 30 odd years) and tanks.
The boiler FAQ is 20 years out of date and don't take it too seriously. Aluminium fitted in a clean system and treated properly every 4 years is fine. It is silicon coated.
But I strongly suggest you go for the Broag 35C or 39C combi using the weather compensation - integral with boiler. Cheaper installation, cheap to run, quality and reliable. And backup if want.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 13 Dec 2008 12:02:55 +0000, MJA wrote:

The silicon coated stuff /should/ be OK. I've put in a few and they seem OK.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I'm interested in what you define as an outdated DHW/CH system. For instance I have a Y plan system with a Honeywell optimising thermostat. If I installed a new boiler what changes, other than a more efficient bolier, is going to make a difference?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

There was clues. Is your cylinder a quick recovery type? Are your rads rated for a 60-40 temp differential?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.