"Capitol" wrote in message
...

I would disagree about the "ball park figure"
being adequate to start with,

Ballpark is fine. There are a few on-line calculators. It is best to use a
few. Ad 5 to 10 % extra if you like.

the odds are you will end up with a
boiler and radiators which are too
small.

The smallest of comi's will do the CH on a "very" large house. The boiler
sizing is not a problem if it is not a big house.

Of more importance, where are the 10 year
maintenance and running costs factored in
on a combi system without soft water.

Always have a de-scaler on a combi, or on "any" system in hard water.

How do these costs compare with a traditional
conventional vented boiler, even allowing
for a tank replacement every 10 years?
Thinking about it, are there any boilers of
any type with a 10 year warranty
even with soft water? In the past, my boiler
life achievements were in excess of 20 years,
have these days gone forever?

Firstly, a combi is a system boiler with a water section. Many share the
same components. Secondly, a combi has most of the "system" in one box.
Only the rads and a wall stat are ouside the box. So when you start
comparing breakdowns and longevity compare like with like. On a
cylinder/tank set up include any problems with the F&E tank, the cold water
storage tanks, the cylinder, the 3-way zone valve, the cylinder stat, the
programmer, all the associated pipework, etc. Then you will find that a
combi is no less reliable, and get a good make of combi, probably far more
reliable overall.

Got it?

I had a Potterton Neatheat for over 20 years. The boiler was very reliable
in itself because there was not much in it. In that time I went through 3
pumps, a zone valve, a zone valve motor, a cylinder, cylinder stat, room
stat and a programmer. On the boiler a relay, flue fan and a pressure
differential switch. Overall the "system" was not that reliable. I am
certain a good Vaillant would have given far less trouble over 20 years.



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