"Andy Hall" wrote in message
...
On Sun, 06 Mar 2005 21:17:44 GMT, Bedouin
wrote:

Over the last winter our (rather old) boiler has been trouble keeping
the house warm. The boiler itself is running continuously but the
radiators do no better than get warm.

We've been living in this house for about 6 years, and not noticed this
as a problem before - but it is possible that in previous years the TRVs
on the rads in the bedrooms may have been turned down lower.

Can anyone think of any likely reason why the boiler should be producing
less than 100% output?

A reasonable possibility is that the heat exchanger is part filled
with sludge. clues here would be noises from it, or if it is
cycling on and off before the radiators are getting hot.

It is possible that some or all of the TRVs are past their sell-by
date and contributing to poor system balance.

Either way, if you are changing the boiler, it will make sense to give
the system a very thorough cleaning and also perhaps replace TRVs if
they are more than about 7 years old.

It may not be worth spending anything on desludging the boiler,
though.




The boiler is an old Potterton Netaheat 16-22 - not the most
sophisticated unit. I am intending to replace it shortly and will use
it as a guide to the correct size of the replacement (which will be
bigger) so need to check that the problem is the boiler being
underspecified for the house rather than just not putting out its rated
output.

Any suggestions gratefully received...

If you want to be rigorous about this, you'd need to do heat loss
calculations. However, if the house has been comfortable with 22kW
before, going for a 28kW boiler should give a comfortable margin.

The pump could be running slow.
Not on full.


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