Heat Exchanger Material?

Opinions please:
I am looking to replace an old Ideal Mexico boiler on an open vented system. I have basically decided to go for a condensing boiler and like the look of the Worcester-Bosch Greenstar 29HE or the Keston Celsius 25.
The main difference I can see between them is that the Keston has a stainless steel heat exchanger, while the Worcester has aluminium / silicon.
Which of these is likely to have the longest life? (A couple of heating engineers have said to me that the a condensing boiler will have a shorter life than a traditional boiler as the condensate gradually corrodes the heat exchanger. Thus my question as to which material is best.)
Also are there any other factors which would make one a better choice than the other?
Any comments would be appreciated. Thanks, Garry.
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wrote:

This is one of the old wive's tails based on the first generation of UK produced condensing boilers. Essentially the manufacturers attempted to adapt existing designs by adding secondary heat exchangers and failed miserably for the reasons you describe. as a result, the technology picked up (unjustifiably) a bad reputation in the conservative trade..
In the rest of Europe, condensing technology has been around for 20 years and most manufacturers are on 4th generation products.
Most of the better ones of these seem to have stainless steel heat exchangers.
On my own, a MAN Micromat, the heat exchanger is stainless steel and warrantied, as is the rest of the boiler for 5 years parts and labour. That doesn't happen if the manufacturer expects a failure after 4 years.
On the other hand, Worcester Bosch have a good reputation with current products. However, I don't know about the longevity of aluminium-silicon alloy heat exchangers.

.andy
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I'd back up Andy's comments. I don't know about the W-B but two useful (to some people) things about the Celsius are that you do the air inlet and flue with cheap muPVC (not ordinary uPVC) 50mm waste pipe rather than expensive flue extensions, and you can remote wire the panel run/fail lights to another location if the boiler is in an out-of-sight location
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system.
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I'm not sure if it does have a stainless heat exchanger. Keston are superb when you have long flue lengths.

heat
Total balls.

Given a choice I would probably go for stainless steel if all other points were equal.

Try the Glow Worm boilers (part of Vaillant Hepworth). Well priced with stainless steel heat exchangers, developed/made in Holland http://www.discountedheating.co.uk
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