De-commissioning back-boilers?
S Viemeister
replaced this year. Currently, we have an oil-fired Rayburn (converted
from solid fuel), _and_ a back-boiler in the livingroom fireplace.
The Rayburn is to be removed, and an externally mounted condensing
boiler will be installed.
The back boiler concerns me - it will, of course, be disconnected from
the heating system, but I wish to be able to continue to use the
fireplace. How does one safely decommission a back boiler? Can this be
done without wrecking the fireplace?
PeterC
Exactly the same here - ex-council, by any chance?
When the CH was fitted I removed the pipes etc. (as no other part of the
system was still there) but have never done the last bit (dI don't use the
fire).
ISTR that the back boiler should be filled with sand, but never checked on
that.
--
Peter.
2x4 - thick plank; 4x4 - two of 'em.
Dave Liquorice
> The back boiler concerns me - it will, of course, be disconnected from
> the heating system, but I wish to be able to continue to use the
> fireplace. How does one safely decommission a back boiler? Can this be
> done without wrecking the fireplace?
Presumably this is an open fire with back boiler? Personally I'd keep
it as a backup/auxillary heat source. Unless it is really kanckerd in
which case your into replacing it anyway to keep the fireplace
operational.
If you want to drain the back boiler and keep the fireplace I think
you have to fill the boiler with sand to prevent (slow down?) it
burning through. Without the water to take the heat away the metal
will get very hot...
--
Cheers
Dave.
Jeweller
> On Mon, 18 Jan 2010 10:24:00 -0500, S Viemeister wrote:
>
>> Our out-dated, hard-to-control, inefficient heating system is due to be
>> replaced this year. Currently, we have an oil-fired Rayburn (converted
>> from solid fuel), _and_ a back-boiler in the livingroom fireplace.
>> The back boiler concerns me - it will, of course, be disconnected from
>> the heating system, but I wish to be able to continue to use the
>> fireplace.
> ISTR that the back boiler should be filled with sand, but never checked on
> that.
We simply left ours in situ and continue to use the open fire.
--
R100RT
Aprilia Pegaso 650 IE "The Flying Mythos"
Formerly: James Captain, A10, C15, B25, Dnepr M16 solo, R80/7, R100RT
(green!)
www.davidhowardjeweller.co.uk
js.b1
http://www.hse.gov.uk/services/localgovernment/boilers.htm
A backboiler behind a real fire (or box-tank behind a gas fire) works
by recovering heat from flue gases, said heat then being used to pre-
heat a HW tank or radiator. Decommissioning such back boilers (or
either type) must be done correctly.
Immediate risk - explosion
Water left in the tank which can not circulate or vent will superheat
- eventually rupturing or even exploding.
Secondary risk - flue gases
If pipes are left vented the tank will eventually corrode permitting
flue gases to be transferred elsewhere, posing a serious CO risk.
The proper solution is...
- Remove the pipes
- Fill holes occupied by pipes with fire cement
- a) Fill the tank with sand & leave ventilated to the flue only
- b) Remove the tank from the fireplace and refill with suitable
bricks, refractory lining as necessary
They are actually quite good at heating water with a gas fire.
However I suspect the decommission cost is rather high even if a
simple "box tank". More substantial dismantling is properly rather
expensive - anyone know?
Beware such backboilers exhibit a winter flood risk when the house is
unoccupied. Cold air plunges down the chimney and over days can cause
the tank &/or pipes to split - the resulting flood from the CW-HW
tanks is either unlimited or still 800L if you have the CW isolated.
I've known 3 fail in this manner, wrecking expensive wooden flooring
and downstairs contents throughout (DG doors meant the water literally
had nowhere to go with solid floors throughout).
cynic
Disconnect the pipes and plug the holes. Drill a couple of small vent
holes at bottom front (you may get some residual water out). Use the
fire as normal. At some stage it will burn through the front panel of
the back boiler at which point you can use fire cement to effect a
repair until such time as you wish to rip it all out and install a
refractory fire back
Onetap
> Beware such backboilers exhibit a winter flood risk when the house is
> unoccupied. Cold air plunges down the chimney and over days can cause
> the tank &/or pipes to split - the resulting flood from the CW-HW
> tanks is either unlimited or still 800L if you have the CW isolated.
> I've known 3 fail in this manner, wrecking expensive wooden flooring
> and downstairs contents throughout (DG doors meant the water literally
> had nowhere to go with solid floors throughout).
Thanks for that. I was aware of the explosion risk ; the freeze &
flood hazard had never occurred to me.
A link to an HSE document on the fatal explosion is below.
S Viemeister
It seems that our short term solution will likely be to
drain/disconnect/remove the piping, making sure that combustion products
can't find their way into the house, and drill holes into the boiler
body. I've seen mention of filling the boiler with sand - but am not
sure how feasible this is - or why it should be done.
The fireplace only gets occasional use, but eventually we'll need to
remove all of the back boiler bits.
Andy Dingley
> I've seen mention of filling the boiler with sand - but am not
> sure how feasible this is - or why it should be done.
Heatsink. If you don't do it, the cast iron back boiler gets to about
400C, cracks and collapses, possibly bringing down some of the
fireplace.
S Viemeister
That makes sense.
Would it be a reasonable idea to make a decent-sized hole in the upper
part of the water jacket (for the sand), along with one or two smaller
ones along the bottom front (for water release)?
cynic
Never come across cast iron firebacks then?
Its probably not cast iron anyway but mild steel.
Andy Dingley
> Never come across cast iron firebacks then?
Yes. They're bedded in mortar, which has a similar heatsinking effect.
If they're not, they can crack too.
Besides which, firebacks are cast in thicker sections than back
boilers.
> Its probably not cast iron anyway but mild steel.
No, mild steel rusts through too quickly.
There's advice linked from the HSE site on a recommended process for
decomissioning. I think this was linked from here recently too. Mostly
(AFAIR) it involved a drilled hole moderately high up, then slowly
pouring dried sand down a pipe.
Adam Aglionby
Any idea what the service life of a back boiler is/was expected to be?
Know someone with a back boiler still in ,er, service,haousing
association , its whole house heating days are long gone, concerned
that its days of safe operation may be past as well...
Thanks
Adam
Adam Aglionby
> Any idea what the service life of a back boiler is/was expected to be?
Should have said , back biler on coal grate fire.
cynic
>
> > Never come across cast iron firebacks then?
>
> Yes. They're bedded in mortar, which has a similar heatsinking effect.
> If they're not, they can crack too.
Quite the opposite to heat sinking, the refractory retains the heat so
the cast iron attains a higher temperature. Solid fuel (coke) boiler
firebars and fireplace grates are also made of cast iron and attain
red heat (1000C) on occasion. When in a hole stop digging!
>
> Besides which, firebacks are cast in thicker sections than back
> boilers.
>
> > Its probably not cast iron anyway but mild steel.
>
> No, mild steel rusts through too quickly.
I should tell Dunsley and other companies who make wrap round high
output solid fuel back boilers from 4 mm mild steel with long service
life. I am sure they will be fascinated by your information.
Roger R
"Onetap" <One...@talk21.com> wrote in message
news:443ae9c0-7cb7-45c1...@m16g2000yqc.googlegroups.com...
> On 18 Jan, 17:12, "js.b1" <js...@ntlworld.com> wrote:
>
> A link to an HSE document on the fatal explosion is below.
>
> http://www.hse.gov.uk/press/2009/coisw61109.htm
The decommissioning leaflet linked from the above page:
http://www.hse.gov.uk/services/localgovernment/boilers.htm
The illustration of a back boiler installation shows that is not acting as
structural support for any of the chimney brickwork.
Is that what I'm likely to find in this 1950's house enabling the boiler to
be taken out without risk of some of the chimney liner brickwork coming
down, or at least needing support ?
Roger R
js.b1
wrote:
> The illustration of a back boiler installation shows that is not
> acting as structural support for any of the chimney brickwork.
From my mother's 1950s (ok 1947-1951) the chimneys are all U-shaped
self-supporting (and supporting joists of rooms above with walls &
ceilings additionally). Lintel may be angle iron, but I suspect it may
be concrete. Very small windows (a foot) use what looks like cast in
place concrete 8in high, larger windows use a smooth grey cement
lintel equally oversized into the room & span, both on slate
padstones. Note however the mortar may be utter crap so beware
cracking particularly if the lintel is above the fireplace opening
which is not unusual (big open fire reduced for gas fire either by
builder or later on).
> Is that what I'm likely to find in this 1950's house enabling the boiler to
> be taken out without risk of some of the chimney liner brickwork coming
> down, or at least needing support ?
People here are referring to cast-iron backboiler, if yours merely
heats the HW tank you may find it is a simple box made of copper. I
assume copper going by the green verdigras all over it.
Drilling a big hole in the top of the front face and tubing very fine
sand in should be effective. When it has water in the temperature and
thus thermal expansion distance is limited. Without water the
temperature can become grossly elevated and thus thermal expansion
distance is much less limited - it could exert significant forces. By
filling it with sand you restrict the temperature it can heat to, thus
limit its thermal expansion distance - and provide a degree of heat
storage.
Sand filling matches the temperature, and better matches the thermal
expansion, of the surrounding brickwork.
If you find blue tiles they are a refractory lining and quite common
in that period. Coal is pretty nasty (acidic) and 1950s mortar pretty
crap really even without coal's onslaught. Wood was often burnt with
chimney fires treated with wild abandon as first attempts at central
heating. Watch out for gas poker taps hidden behind kitchen units,
they are invariably still live :-) I am also dubious that some gas
fires are supplied by what were originally pipes sized for gas pokers
and due to distance combined with small bore have historically been
"passed over" re pressure drop limits :-)
With backboilers of that era you will probably find the pipes into the
chimney are not well sealed - they should be sealed with fire cement
but rarely are, it's often polyfilla collecting together various
previous cracked attempts into a wallpaperable but non-sealed ensemble.
Roger R
"js.b1" <js...@ntlworld.com> wrote in message
news:e022dba0-a301-4c67...@m16g2000yqc.googlegroups.com...
On Jan 20, 9:26 pm, "Roger R" <decoder.inva...@clara.invalid.co.uk>
wrote:
> The illustration of a back boiler installation shows that is not
> acting as structural support for any of the chimney brickwork.
:From my mother's 1950s (ok 1947-1951) the chimneys are all U-shaped
:self-supporting (and supporting joists of rooms above with walls &
:ceilings additionally). Lintel may be angle iron, but I suspect it may
:be concrete. Very small windows (a foot) use what looks like cast in
:place concrete 8in high, larger windows use a smooth grey cement
:lintel equally oversized into the room & span, both on slate
:padstones. Note however the mortar may be utter crap so beware
:cracking particularly if the lintel is above the fireplace opening
:which is not unusual
All original, and with concrete lintles for window openings so probably
ditto for fireplace.
Lime based weak mortar with sand and lime (white) internal bricks.
> Is that what I'm likely to find in this 1950's house enabling the boiler
> to
> be taken out without risk of some of the chimney liner brickwork coming
> down, or at least needing support ?
:People here are referring to cast-iron backboiler, if yours merely
:heats the HW tank you may find it is a simple box made of copper. I
:assume copper going by the green verdigras all over it.
Perhaps you are confusing me with someone else - I havn't posted any
picture.
The back boiler is indeed only for the hot water tank, but is a cast iron
type with a removable panel above a coarsly ribbed lower part. Below this
ribbed tank is a gap allowing the hot gasses to pass under and around the
back. The hot gasses are diverted by means of a sliding plate out of sight
on top of the unit. The brand name on the front face is 'Redfyre'.
Photo available later.
Roger R
Andy Dingley
> > Yes. They're bedded in mortar, which has a similar heatsinking effect.
> > If they're not, they can crack too.
>
> Quite the opposite to heat sinking, the refractory retains the heat so
> the cast iron attains a higher temperature.
Rubbish. Whilst it's going to "retain the heat", all that's going to
do is to keep it warmer in the morning, after the fire has gone out.
Peak temperature when lit for a piece of thin cast iron is going to be
higher for a plate with an air gap insulation behind it, compared to
masonry in reasonable contact. It's about the dynamic equilibrium of
heat flow in vs. out when burning (i.e. conduction), not about heat
storage (i.e. heat capcity).
> Solid fuel (coke) boiler
> firebars and fireplace grates are also made of cast iron and attain
> red heat (1000C) on occasion.
Firebars are made of two different metals: some are a simple grey cast
iron, others an austenitic stainless. Parkrays and similar use a mix,
with the better steel in the middle where it's hotter. If you put them
in the wrong place under a coke fire, the plain grey iron doesn't last
at all long.
Mostly though, firebars are just that: bars. The reason they're
installed as separate bars is to stop cracking and warping like this.
The bars are free to move (compared to a one piece grate) so that they
don't crack (they'd warp first) and any slight warping is absorbed in
the rattle space around them. Although solid one-piece grates were
used for a long time, they didn't work for the higher temperatures
when we switched from coal on open grates to coke in enclosed box
stoves.
Also, "red heat" is around 600 to 800 C. 1000 C is a pale yellow.
Although you can achieve orange heats within the coals of a domestic
fire, you won't get the ironwork to 1000 C.
Grimly Curmudgeon
drugs began to take hold. I remember Andy Dingley
<din...@codesmiths.com> saying something like:
>> Its probably not cast iron anyway but mild steel.
>
>No, mild steel rusts through too quickly.
Not if it's 6mm thick to start with. I have a rescued BB that's 20 years
old and still plenty thick. I intend to re-use it and expect it to last
for many years yet.
Grimly Curmudgeon
saying something like:
>Any idea what the service life of a back boiler is/was expected to be?
I know of many that are 30 years or older.
zo...@cwgsy.net
Zoe
Tim Watts
> Putting a new back boiler in safely. Plumber says boiler for water not safe to put pump on for radiators ? Why not if bubbling means time to circulate? And nice and hot?
> Zoe
>
Dave Liquorice
> Putting a new back boiler in safely. Plumber says boiler for water not
> safe to put pump on for radiators ?
the heat in the boiler or it will boil and when they do it's not a
gentle little bubling noise but sodding loud bangs an wooshing
noises.
There can be a pump to circulate water around the rads but it must
not be in the gravity loop to the HW cylinder and/or heat dump
radiator.
Is the back boiler the only source of heat for the system or is there
also a gas/oil boiler as well? Getting them to play nicely together
is beyond most "plumbers". It's not difficult but you need to know
what you are doing.
--
Cheers
Dave.
johnrow...@gmail.com
they recommend removal of back boiler rather than venting although this is an option.
having worked in the industry some 16 yrs, my safety concerns are fumes and smoke usually find their way up the redundant channels and pipes ! Stick to HSE guidlines would be my advise.
Andrew
You obviously didn't and are 8 years too late. Where did you trawl
up this old posting from ?.
And making reference to the HSE on DIY newsgroup isn't going to make
you very popular, especially if you actually work for them.
Graeme
<Andrew9...@mybtinternet.com> writes
>> On Monday, January 18, 2010 at 3:58:56 PM UTC, Jeweller wrote:
>
>You obviously didn't and are 8 years too late.
--
Graeme
Brian Gaff
moved in here did not even realise there was a back boiler in the fireplace,
it was only later on when we needed a new hot water cylinder that the
plumber found it which had been disconnected and stop ends put on the pipe
it was still full of water and had not leaked after over 30 years. He of
course stuck a hose on a tap at the bottom and drained it. It was amazing
that we had not had a flood in those 30 years or so.
Maybe they made things a little better back in the 1930s!
Brian
--
----- --
This newsgroup posting comes to you directly from...
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Blind user, so no pictures please
Note this Signature is meaningless.!
<johnrow...@gmail.com> wrote in message
news:f3a6cce3-2946-4ef8...@googlegroups.com...
Marland
> Blimey this thread has a checked history over many years, but we when we
> moved in here did not even realise there was a back boiler in the fireplace,
> it was only later on when we needed a new hot water cylinder that the
> plumber found it which had been disconnected and stop ends put on the pipe
> it was still full of water and had not leaked after over 30 years. He of
> course stuck a hose on a tap at the bottom and drained it. It was amazing
> that we had not had a flood in those 30 years or so.
> Maybe they made things a little better back in the 1930s!
> Brian
>
original disconnection did exactly what should not be done. A drained back
boiler is just a lump of Iron or occasionally copper which will get very
hot which may or may not matter depending on what surrounds it, one full of
water and capped becomes a sealed pressure vessel and if it or bits of
capped pipe connected to it rupture under pressure then the results can be
nasty, low end is a split and you get a puddle for a while, high end is a
sudden explosive failure which could well be strong enough to cause a lot
of damage especially if it blows the contents of the burning grate into
the room over everything including occupants.
Ideally a disconnected back boiler and piping should be filled with sand
though if it is left uncapped pressure should not build up.
GH
S Viemeister
> Brian Gaff <bri...@blueyonder.co.uk> wrote:
>> Blimey this thread has a checked history over many years, but we when we
>> moved in here did not even realise there was a back boiler in the fireplace,
>> it was only later on when we needed a new hot water cylinder that the
>> plumber found it which had been disconnected and stop ends put on the pipe
>> it was still full of water and had not leaked after over 30 years. He of
>> course stuck a hose on a tap at the bottom and drained it. It was amazing
>> that we had not had a flood in those 30 years or so.
>> Maybe they made things a little better back in the 1930s!
> original disconnection did exactly what should not be done. A drained back
> boiler is just a lump of Iron or occasionally copper which will get very
> hot which may or may not matter depending on what surrounds it, one full of
> water and capped becomes a sealed pressure vessel and if it or bits of
> capped pipe connected to it rupture under pressure then the results can be
> nasty, low end is a split and you get a puddle for a while, high end is a
> sudden explosive failure which could well be strong enough to cause a lot
> of damage especially if it blows the contents of the burning grate into
> the room over everything including occupants.
>
> Ideally a disconnected back boiler and piping should be filled with sand
> though if it is left uncapped pressure should not build up.
>
and was filled with sand.
And the new combi has saved a fortune in heating costs.