Cavity wall installation damaged chimney

It seems that when our cavity wall cowboys installed the insulation recently they 'accidentally' drilled into one of our chimneys. They spotted this and filled in the holes in the bricks/mortar from the outside. However a gas installer fitted a fire last week and spotted there was further damage on the inside of the bricks where the drill had taken a bigger chunk out of the inner side of the brick. The gas bloke filled in the other side of the brick he could see within the fire place but said the others further up teh chimney could be damaged the same.
he suggested that the chimney wouldn't function correctly and that fumes could seep up the bricks somehow and then filter into the loft. (I'm paraphrasing what my wife has told me the installer said).
What I can't understand is how or why the damaged bricks would affect the chimney, even if the bricks have vents in them the fumes can only reach the next layer of mortar surely? Do I need to take out all teh damaged bricks and replace or is he thinking something else is wrong.
I'm considering dropping a carbon monoxide detector into the loft to see whether anything is seeping for the time being but just don't fancy damaging the chimney any more than the cowboys did iin the first place.
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Woby Tide wrote:

Line the chimney..Its not cheap but frankly its a safety thing that is well worth the expense.
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The safety is more my concern, however regardless of cost I'm not sure that I should be paying if the cavity installers have damaged what was a 'working' lined chimney. As yet though I still couldn't quite fathom what the potential risk was and how the damaged liner affects this
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Woby Tide wrote:

If you could see bricks inside it it wasn't lined mate.
IIRC you have to have it lined with either glazed ceramic flue liners or a steel pipe these days for it to be considered 'lined'
Now gas fires are not as onerous as wood fires..but even so, there are regulations that effectively prohibit use of a simple stack made of bricks or blocks..its all to easy for mortar to crumble out and gases - toxic OR inflammatory - to leak out.
Normally you would not be allowed to install a gas fore in a flue without a liner these days. A flexible steel on at a minimum if its pre 1970's stack.
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It's a 1930's house, looking up inside it appears to be a creamy/sandy texture which from what I've read is some sort of lime mortar lining. I can see where the gas bloke has filled in the hole in the 'lining' using something similar. I guess there are further similar 'holes' further up. they are sealed from the outside with mortar but I guess there must be two/three smallish gaps on the inside where the mortared brick is, probably about 2 inch diameter where the lime mortar will have come away when drilled. I guess one option is to switch to a steel flue liner and have done with but as the previous lining was fine till it got drilled bit annoying, we don't use the fire that much, it just now seems to be shedding a bit of the lime mortar when it's very windy.
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Woby Tide wrote:

IN which case I am about 90% sure you can simply use a flexible lining, dropped in from the top.
I really recommend it anyway..its a sort of point that may conceivably save the house one day.
Round our parts, there are at least 15 fires a year due to blown mortar in old stacks allowing flames through to the timberwork - and often thatch work as well. Our neighbour is a part time fireman..and a damn useful man to know..he's cast an eye over what I have and pronounced it safe..
.
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In article < snipped-for-privacy@a75g2000cwd.googlegroups.com

I agree with you and think it is a non issue.

The CO detector certainly won't do any harm.
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fred
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That's the wrong tool for the job. The fire won't be generating CO in the first place unless it's faulty. I believe smoke pellets are used for checking for chimney leaks.
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Andrew Gabriel
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Andrew Gabriel wrote:

And in any case its not what's happening NOE that is the problem..its what might happen one day..
Line it.
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Just generally or because of this damage? If it's because of this damage then a) it's only a potential leak in the outer skin ie to the outside air and b) as the o/p points out a leak isn't able traverse the wall to somewhere more critical through the mortar joints. Lining for that reason appears an unnecessary expense.
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fred wrote:

Just on principal really. I would not consider a stack that had any internal surfaces and which relied on mortar joints to be good practice or safe.
Originally they would have been lined with a nice coating of soot..but even then chimney fires could happen and blast pretty hot gasses into surrounding timberwork.
Maybe I am just fussy..brother in laws house burnt down almost to a shell, and as I said, my neighbour is a fireman. The risk is low, but the consequences are high. Insurance never covers everything. Why take the risk when a few hundred quid of steel liner brings the thing entirely up to standard and probably reduces whatever risk there is to almost nonexistent proportions?
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Gotcha and I'd be inclined to agree if the o/p was doing anything other than installing a gas fire but the flue gasses just aren't hot enough to cause the fire risk you're concerned about. Flames licking up the chimney, soot to catch fire or tars from log burning then fine but for the o/ps use it seems unwarranted. Going back to the original question, I don't think the chimney is any more dangerous as a result to the cowboy damage.
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fred wrote: <snip>

And I'd just like to add that they weren't cowboys anyway, how is any CWI installer supposed to know whether the wall behind the chimney is single brick, double brick or has a cavity going straight across? - if it's the latter, it should be insulated as this is where most heat will escape from, and I seriously doubt the word of the second workman on the premises who has sold this idea of a damaged chimney to the customer - the largest piece of brick I have ever known to blow off the back of a brick was no larger than a matchbox, hardly chimney blocking material, even if he drilled a dozen holes through - and all holes will be pointed up externally, which means there is no added, or diminished draught, IE, nothing has changed.
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I don't think there's any excuse for breaching the chimney, if it had previously been found to be leaking and lined with a flexible liner then that could easily have been breached by the drilling which would have been seriously bad news.
In the workmen's place I wouldn't have drilled near the line of the chimney unless I was certain it wasn't single brick. They could have checked that by depth measurement if the fireplace was open but then again there's no need to drill on the line of the flue opening, drill either side and the foam or fibre will flow if it's a cavity and not if it's solid, single or double.
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because they install CWI for a living, you'd think they may have come across a house with a chimney before and give it a bit of forethought, because after the first time the drill goes through the cavity they could check, rather than drilling into it four times and then realising on the bottommost one that they'd filled the fireplace with crap
this was before I discovered they also hadn't replaced/closed off all the air bricks around the house which were now filled with insualtion material, they came back out to replace them all a few days later
and just before they did a smoke test and put the 'expired' match onto the mantelpuece causing it to scorch
So IMO they are cowboys at Snugasabug/Instafoam and Fibre Ltd Woking
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Woby Tide wrote:

No one has any experience on anything these days.
After all, they all probably are grajates with meejah studdies digrees.
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