On 08/04/2012 14:36, David WE Roberts wrote:

"John Rumm" wrote in message
...
On 06/04/2012 19:06, David WE Roberts wrote:
snip
If there was an explosion it would probably be due to heating a
depressurised system and generating steam in a sealed system.

Well that is a different situation from a gas explosion... or late
ignition.
snip

Thanks as usual, John.

To clarify just this little bit, I was talking about the general
explosion risk if the boiler had not been modified (which as you say
should be quite low)

Careful not to conflate things though... it can get a bit confusing when
talking about sealed / unvented / pressurised primary systems and sealed
/ unvented / pressurised hot water systems. The two are unrelated.

Using a boiler on a sealed primary that has not been appropriately
modified or augmented, is a risk, and it may only take something simple
like a failed pump to cause that risk to manifest and break something in
a not good way.

This is a separate issue from the inherent risks of an unvented hot
water system. Those risks are very low when the heating of it is
indirectly via a CH boiler.

as opposed to the minor gas explosion that they had
which should be another issue entirely (although worrying).

A bit depends on exactly what and how bad... for example, years ago we
had a Main multipoint water heater that would after a while suffer
percussive ignition - so rather than lighting the main burner quietly it
would start with a noticeable thump. This was usually an indication that
the pilot light nozzle had accumulated a little soot, and was not
igniting as fast as it should (it was a two stage ignition, spark to
light pilot, thence main burner). Jiggling the burner jests aside and
removing the pilot burner, poking some fine fuse wire through it would
clear any obstruction and it would be fine again for about 18 months).





--
Cheers,

John.

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