Glow Worm Energy Saver...
The Glow Worm Energy Saver is a early example of a low water content
('Low water content' boilers have heat exchangers constructed from cooper
tubing with heat-collecting fins attached, as opposed to having a conventional,
one-piece cast iron heat exchanger.)
Like most early condensing boilers the Energy Saver has two heat exchangers
rather than one. The primary heat exchanger collects the majority of the heat
from gas flames burning on a conventional burner below, like an ordinary
boiler. Flue gases are then routed through a secondary heat exchanger is
fitted above, which removes more heat and the condensate thus generated is
collected in a tray arrangement below this secondary heat exchanger and
connected to a drain.
Being a condensing boiler, fuel efficiency is high. Fuel efficiency is quoted on the SEDBUK database as between
86.6% and 87.9%
depending on the exact model you have. OK but not great for a condensing
boiler. (Modern condensers usually exceed 90%.)
Unfortunately the Energy Saver is not well-regarded amongst heating
engineers. It is seen as a poor design with latent flaws which would have been
revealed had the boiler been properly field-tested and not rushed to market
The main problem is the condensate collection tray under the secondary heat
exchanger. Condensate is slightly acidic and the collection tray is made from
aluminium - a fatal design flaw with hindsight. The condensate corrodes through
the tray in just a few short years, leading to water dripping from the bottom of
the boiler whenever it is running.
Now the news gets bad. Had the boiler been designed with this susceptibility
to corrosion of aluminium in mind, the designers would have made the collection
tray an easily replaceable part. Unfortunately, they didn't. The collection tray
is an integral part of the secondary heat exchanger and the whole (very
expensive) assembly has to be changed to repair this fault when it occurs.
Most users decide, when faced with a bill of many hundreds of pounds for
fitting a new secondary heat exchanger assembly, to replace the whole boiler
instead. Especially when they consider that there is no reason to expect the new
part to last any longer than the old.
If you have an Energy Saver, my view is that it would be a good idea to
change it before you run into this problem.