On 26 Jul, 09:35, Stephen
wrote:
On Thu, 24 Jul 2008 07:12:28 -0700 (PDT), cynic

wrote:
He is an opportunist ******* posing as a salesman! The case in
question was an electric immersion heater with a one stage (failed on)
thermostat. The tenants ignored the bubling and banging (were they
deaf or simple?)

As it happens I occasionally hear the odd bubble first thing in the
morning when we use Economy seven to heat the water. The immersion
heater is set to 60C. Is an odd bubble ok or does it mean the
thermostat is a bit iffy?

An odd bubble means very little A boiling system will thunder and
crash continuously until it runs out of water or someone hears it who
has sufficient brain to switch off.


The header tank was not fully supported but rather
balanced on two joists so it sagged and split pouring boiling water
onto the ceiling which softened and collapsed with a cot beneath it.

I would have thought a plastic tank would melt at high temperature no
matter how it was supported but I can see that in that scenario, the
lack of support may have speeded things up. I am reassured that our
tank sits on a sheet of plywood over a number of joists.

The relative efficiency is another matter but if you had told us what
model you have it would have enabled us to estimate the likely
benefits.

It is a Mistral M1A. The manufacturer cannot find the serial number in
records for the last fifteen years, so they think it is 18-20 years
old. The manufacturer told me that the boiler would have been 65-70%
efficient when new but loses 1% per year so is now about 45-50%
efficient.

Of course, like the plumber, they have a commercial interest to sell
me a new one. Does the above ring true or does it sound a little
fishy?

Could be within expected limits. the 1% per year sounds unlikely as I
would expect an initial drop then a fairly stable lifetime. Your
service engineer should take combustion readings and your report sheet
ought to show the nominal efficiency based on the temperature
differential of inlet air to flue outlet related to the CO2 content of
the flue gas. Its a close approximation!


When I bought oil last time (Jan 08) *it was £400 for 1000L. I heard
someone bought 1000L recently for £800. The manufacturer (Mistral)
said that a new boiler would be 95% efficient and mine is 50%. Will my
old boiler will use twice as much oil (95/50=about 2) or is it not as
simple as comparing efficiencies?

I seriously doubt your Mistral (I think its a pressure jet burner) is
down to 50%, nearer to 70% if it has been kept in a reasonably well
maintained condition.


If so, I was thinking that in three years the cost of a new boiler
(£1200) would equal the cost of the saved oil. Or are my maths wrong?


Oh and one last point -most plumbers have no idea about how an oil
boiler works!

I searched through the Yellow Pages to try and find an OFTEC one, so I
had hoped this chap knew more than most.

If he is OFTEC registered he ought to know the basics but has he any
good references from other customers?
OFTEC are somewhat similar to CORGI in that they offer registration
for different categories of work. Make sure your guy is ok for boiler
installation and commissioning from his ticket. Or you could ask OFTEC
for confirmation.