On Wed, 1 Mar 2006 21:19:18 +0000, mark
wrote:

Planning to replace my old combi with a new boiler.
I plan to use a Vaillant Ecomax 635e system boiler hooked up to a
250litre unvented cylinder.
Im thinking about using a weather compensator:

http://tinyurl.com/qre3a

Anybody got one?
Any opinions on how good/bad/indifferent this boiler is?


I can't comment on that boiler specifically, but I do have one (MAN
Micromat) with a weather compensator based on the same principle of
monitoring the outside temperature and adjusting the boiler output to
match.

It works very well in terms of maintaining the set temperatures in the
house without needing to cycle the boiler on and off.
For example, I noticed this afternoon that there was a drop in
temperature of about 2 degrees over quite a short time. The boiler
had been poodling along at about 5kW output across the middle of the
day, but began increasing output as it became colder.

The room thermostat is also "analogue" in behaviour in that it will
indicate temperature changes to the boiler, again modulating it rather
than cycling it. This results in very constant temperatures -
typically under half a degree of variation. I notice from the
brochure that the Vaillant one has this feature as well. Again I'd
say worthwhile.

I also have the same thing for the hot water cylinder - i.e. an
analogue sensor rather than strap on thermostat. This fits into a
pocket in the cylinder. With this, the boiler switches to hot water
mode when the temperature is 5 degrees below the set point
(adjustable) and then modulates down at the end of the burn to avoid
overshoot and higher temperature than the set point. This is nice,
but I think not as important as the other two.


One comment that I would make is that if you are going to go for a
large cylinder and 35kW boiler, do make sure that the cylinder is a
fast recovery type - not just a part L1 model. Otherwise you will
find that during HW recovery, the boiler may well modulate down to
half to 2/3 output if the heat isn't transferred fast enough. Most of
the major manufacturers have these - e.g. Albion cylinders. etc.


--

..andy