This my third go at getting somewhere with my ailing boiler.
The problem now appears to be that the thermocouple is failing at high
temperatures. So it will stay on all night but it will stop working after
the boiler runs for 10 minuites or so.
Does anyone have any experience of this?
I have put in a new thermocouple but the same thing is happening.

Any thoughts

Stony

This my third go at getting somewhere with my ailing boiler.
The problem now appears to be that the thermocouple is failing at high
temperatures.

If your boiler is old enough to take a thermocouple, you might want to
consider replacing it. A modern boiler would have 90%+ efficiency, instead
of the 50-65% you are likely to be getting now. It may be worth making a
judgement on whether or not a replacement would make financial sense,
particularly if the old boiler is starting to keel over. There's a lot of
gas to be saved.

Christian.

"Christian McArdle" wrote in message
t...
This my third go at getting somewhere with my ailing boiler.
The problem now appears to be that the thermocouple is failing at high
temperatures.

If your boiler is old enough to take a thermocouple, you might want to
consider replacing it. A modern boiler would have 90%+ efficiency, instead
of the 50-65% you are likely to be getting now.

Can you explain how you calculate efficiency - is it for example :
Given the amount of heat ( in say joules ) that is released by the burning a
specific quantity
of gas, find the amount of heat transfered to the water and take the
quotient ?

Steve

Can you explain how you calculate efficiency - is it for example :
Given the amount of heat ( in say joules ) that is released by the burning
a
specific quantity
of gas, find the amount of heat transfered to the water and take the
quotient ?

It is far more complicated than that. In fact, under the calculation method
used, it is even possible to get more than 100% under certain conditions.
However, it does approximate the potential absolute efficiency in
translating fuel energy into useful heat energy that may be distributed
around the system. See www.sedbuk.com for details.

Christian.

"Christian McArdle" wrote in message
t...
Can you explain how you calculate efficiency - is it for example :
Given the amount of heat ( in say joules ) that is released by the
burning
a
specific quantity
of gas, find the amount of heat transfered to the water and take the
quotient ?

It is far more complicated than that. In fact, under the calculation
method
used, it is even possible to get more than 100% under certain conditions.
However, it does approximate the potential absolute efficiency in
translating fuel energy into useful heat energy that may be distributed
around the system. See www.sedbuk.com for details.


So this calculation may give an efficiency of greater than 100% - if so, I
believe this is breaking the
well tested empirical laws of thermodynamics. ( Can any physicists help, my
memory is bad ). The boiler manufacturers should immediately publish this
result :-) I suspect that that, rather than this being the case,
the boiler is nowhere near 100% efficient - the obvious example is the fact
that they all chuck heat out
the flue - even the condensing ones.

What I would be intersted in is :
- A sensible definition of efficiency
- the reason why modern boilers claim such a big efficiency increase over
the older designs - are you comparing older non-condensing boilers with
newer condensing designs.

I couldnt find the calculation details you mention - where is it on the
sedbuk site ?

Steve

I couldnt find the calculation details you mention - where is it on the
sedbuk site ?

There isn't an actual methodology on the site that I've found. However, it
does state that the calculation makes various assumptions and calculations
based on the likely heating profile required in the UK. It isn't a simple
energy out/energy in calculation at all.

Christian.

In article ,
"Stoney" writes:
This my third go at getting somewhere with my ailing boiler.
The problem now appears to be that the thermocouple is failing at high
temperatures. So it will stay on all night but it will stop working after
the boiler runs for 10 minuites or so.
Does anyone have any experience of this?
I have put in a new thermocouple but the same thing is happening.

Yes, I've seen the same problem with a gas fire which Eastern Gas fitted.
Problem was too large a pressure drop when the main jets were lit,
which resulted in pilot light shrinking. They had to come back and
take a feed from the gas main, rather than running it from an old
gas lamp pipe.

Have you checked the pilot flame's size/shape against the servicing
manual? It might be that it's misshapen due to partial blockage,
and the change in airflow when the main burner lights is taking it
away from the thermocouple. Another possibility is the thermocouple
isn't mounted at the right place/height. Another thought that occurs
to me is the flue's blocked, causing the flames to drift into the
wrong place due to lack of airflow (and consequent risk of CO release).

--
Andrew Gabriel

"Andrew Gabriel" wrote in message
...
In article ,
"Stoney" writes:
This my third go at getting somewhere with my ailing boiler.
The problem now appears to be that the thermocouple is failing at high
temperatures. So it will stay on all night but it will stop working
after
the boiler runs for 10 minuites or so.
Does anyone have any experience of this?
I have put in a new thermocouple but the same thing is happening.

Yes, I've seen the same problem with a gas fire which Eastern Gas fitted.
Problem was too large a pressure drop when the main jets were lit,
which resulted in pilot light shrinking. They had to come back and
take a feed from the gas main, rather than running it from an old
gas lamp pipe.

Have you checked the pilot flame's size/shape against the servicing
manual? It might be that it's misshapen due to partial blockage,
and the change in airflow when the main burner lights is taking it
away from the thermocouple. Another possibility is the thermocouple
isn't mounted at the right place/height. Another thought that occurs
to me is the flue's blocked, causing the flames to drift into the
wrong place due to lack of airflow (and consequent risk of CO release).

On my old gas boiler, apart from the occasional thermocouple (2 in 20
years), the problem has been minute particles of dirt in the gas supply
slowly blocking up the pilot light.

The symptoms (as suggested above) are a pilot light that is small, and does
not really cover the thermocouple well.

Stays in overnight but doesn't survive after the first long burn.

The cure for me is to remove the pilot jet, and clean it out with fuse wire.

Crude, but effective.

Once you have done it, you can easily see the difference in the flame.

You could even get a spare jet (cheap enough) and fit the new one then clean
the old one as a backup.

HTH
Dave R

P.S. Christian - do they do direct replacements i.e. ground floor boiler in
the centre of the house using chimney flue, or do all modern boilers vent
directly (or nearly directly) to the outside?
There is a vast difference between the strategy for direct replacement and
moving all the pipes to an outside wall.

P.S. Christian - do they do direct replacements i.e. ground floor boiler in
the centre of the house using chimney flue, or do all modern boilers vent
directly (or nearly directly) to the outside?

You probably don't want an old open flue system. You wouldn't get all the
cost saving benefit of modern fan flued (and condensing) designs. However,
most boiler's flue systems could be shoved up a chimney. If it is
particularly long, the Keston Celcius 25 has the cheapest, as it is run with
a couple of plastic drainpipes.

A typical modern boiler can cope with an effective flue length of around 20m
(some are better, some are worse). A bend adds a metre or two to the
effective length. The flues can be run horizontally (with a slight incline
to allow condensate to drain) or vertically.

In some ways, a chimney is the ideal place to run a flue, as the plume
discharge is well away from the windows and no-one minds the steam floating
away from the terminal in quite the same way, as it is evocative of the old
coal burning days.

Christian.

"Stoney" wrote in message
...
This my third go at getting somewhere with my ailing boiler.
The problem now appears to be that the thermocouple is failing at high
temperatures. So it will stay on all night but it will stop working after
the boiler runs for 10 minuites or so.
Does anyone have any experience of this?
I have put in a new thermocouple but the same thing is happening.

It could be that this is what it's meant to do: some open-flued appliances
(generally gas fires, but maybe some boilers?) have a 'vitiation' device -
an arrangement for detecting that oxygen levels in the air being drawn in
for combustion are dangerously low, and shutting down the appliance. If you
fix this 'problem' it could be the last one you'll fix :-|

Is the boiler in an enclosure of some sort, and if so does it have
any/enough ventilation? Are the main burner flames nice and regular shaped
and blue or straggly and yellow? I would not expect vitiation (depletion of
oxygen) to occur in any reasonable-size room within 10 minutes but there are
some unusual combinations of the location of the boiler and its flue
relative to the natural airflow within the house, which can cause combusion
products not to discharge up the flue but to hang around and starve the
boiler (and cause carbon monoxide production!).



--
John Stumbles
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