Boiler Flue Issue

[Julian]

I have a Worcester-Bosch Highflow 440 combi boiler. I started noticing a few years ago that on the terminator that sticks out of the wall the plastic tube coming out of the very end was starting to disappear. The picture in this post that I found when googling for all things flue-related could almost be a photo of my flue as it was when I started noticing the issue a few years ago, it shows perfectly what I have...

https://www.pistonheads.com/gassing/top ... &t=1241107

Recently the whole of the final plastic projection has disappeared apart from a little sliver of plastic at the bottom. At first I thought it was melting but it is interesting to see the guy on the post linked to above say that his "seems to have shattered in the frost". That would seem to make sense since one would assume the flue is engineered for heat. Also, we've had scaffolding up recently on the wall where my flue comes out and I wonder whether the scaffolders putting up the scaffolding or the workmen subsequently working on it might have broken off the final bit. I've been away for a few months so wasn't there to see what was going on.

The scaffolding has given me the opportunity to go out and have a look after the builders pack up for the day and the final bit of plastic at the bottom is very crumbly, I easily broke a bit off with my fingers. Also, with the boiler running none of the flue feels particularly hot (it is a condensing boiler after all which I believe means that it extracts heat from the flue gas as best it can) so I doubt it was ever a heat/melting problem and maybe was a frost issue. I am away in the winters and don't have the boiler running so the flue would have been cold.

Anyway, I'm now left with what to do and that's becoming a nightmare. One company that I got round to look at it said that they couldn't replace it because if they did then new work would need to comply with latest standards and the flue comes out into a big approx (5m x 5m) light well and exits about 2.7m below roof level whereas latest regs apparently say it should be no more than 1.1m below the top of the light well. There's all sorts of other stuff in the way, both on the inner and outer walls, so it's going to be a nightmare to fix. The obvious solution of fitting a plume management kit isn't an option because one isn't available for my flue.

I'm now wondering exactly what purpose that final bit of plastic tube fulfils and whether one option might be to do nothing. Some posts from plumbers on one plumbing forum (for which I now lost the link) suggested that in theory it reduced the risk of any carbon monoxide getting back into the air intake but was one of those things where everything would probably be just fine although if a plumber sees it it is an item they are supposed to flag and shut off the boiler.

Since fixing this is looking like it will cost me over a thousand pounds, possibly well over since the scaffolding is coming down next week and if I cant get an engineer in the next few days I would have to re-scaffold at my own cost, I'm actually wondering whether neatly cutting off the final bit of plastic tube at the bottom while I still have scaffold access and hoping no one picks it up (i.e. pretty much do nothing) might be one option. Other flues in my light well seem to have no plastic tube projecting, in fact they look very much like mine would look like if I were to do the above.

One other slightly more ambitious option that occurs to me is to get a length of 85mm diameter metal tube which I could fit to the outside of that little metal lip just before the plastic tube becomes visible to keep a bigger separation between where the flue gasses come out and where the air intakes are. I think that would be pretty simple to do and I've found a suitable pipe for £15 which is a heck of a lot cheaper than the £1,500 it looks like it would cost me to get it officially fixed which essentially involves reworking the entire flue.

Any thoughts, comments, other suggestions?

- Julian

[Itsallaguess]

Any thoughts, comments, other suggestions?

If it's the same as this one then it looks like the pipe-extension had an anti-nesting grill on it too, as well as taking the exhaust away from the inlet-grill -



https://www.wolseley.co.uk/product/worcester-bosch-horizontal-flue-kit-80---125-mm-p100824-44/

On the above image, it looks like there's screws available to take the silver end-cap off that houses the extension-pipe, which might mean a swap-out with a proper replacement part, or at least the end of it, is perhaps an option?

On a separate note, did you get a second opinion regarding your gas-bod saying he couldn't fix the flue, as any repair would then have to comply with current regulations?

I'm only asking because I'd want to make sure this is definitely the case, and that repairs to existing flue-installations do always need bringing up to the latest installation standards...

Grand-father rights exist in many regulatory areas, so it might be worth double-checking this with a different company, just in case....

Cheers,

Itsallaguess

[Itsallaguess]

Since fixing this is looking like it will cost me over a thousand pounds, possibly well over since the scaffolding is coming down next week and if I cant get an engineer in the next few days I would have to re-scaffold at my own cost, I'm actually wondering whether neatly cutting off the final bit of plastic tube at the bottom while I still have scaffold access and hoping no one picks it up (i.e. pretty much do nothing) might be one option.

This looks like a direct replacement from Ebay (as new) for about £64 delivered -

https://www.ebay.co.uk/itm/Worcester-Bosch-Horizontal-Flue-Kit/223477515445

It says 125mm on the detail lower down, but do check your own pipe diameter, of course...

Cheers,

Itsallaguess

[Julian]

Thanks itsallaguess. That second one does look exactly like my unit. The problem is though that it isn’t as modular as one might imagine. I was pretty incredulous when they told me that the whole unit needed to be replaced but then I went out onto the scaffolding and had a look myself. The problem is that the clear plastic pipe sticking out at the end isn’t a separate bit, it’s simply the final 15cm or so of a plastic inner core that runs the whole length of the flue assembly and then mates with the next section of the flue inside my flat. Using that kit, whatever the price I pay, involves removing the entire current unit, I.e. breaking away the concrete seals where it went through the wall, exposing the inside flue, re-inserting the new piece, mating it securely with the inside section of the flue (which due to potential for CO leakages I would want done by a professional gas engineer) and then resealing it all. That was bad enough but then I was told today that they couldn’t even do that because, as previously mentioned, they couldn’t reinstall the outlet in the same place.

I’m actually thinking that what I might do just to be safe is get a 25cm length of 75mm outer-diameter PVC pipe (https://www.plasticpipeshop.co.uk/75mm- ... _1175.html) which should then slide very snuggly inside the existing 80mm pipe assuming the wall thickness of the 80mm pipe is no more than 2.5mm. I’ll need to go and measure it tomorrow. I could then simply push the pipe about 10cm in so that I end up with the discharge pipe protruding about 15cm from the end of the metal as it was before. I wouldn’t be concerned about doing this myself because I wouldn’t be tampering with any of the existing flue work or going anywhere near existing joints, I’d simply be extending that outside pipe back to length. The little internal lip it would create inside the inner flue pipe shouldn’t be an issue since the flue is designed/installed such that the condensate runs back into the boiler and the total flue run is only about half of what the spec allows for so the absolutely minimal extra amount of extra back pressure that the final 25cm of slightly narrower pipe creates wouldn’t be an issue at all, in fact there is an alternative 60cm flue option I think for shorter total flue length installations so the 75mm end section would be no issue for my installation (my actual flue run is about 7m vs a maximum spec of 13m for my boiler using a horizontal 80/125 flue).

I really don’t think I can face spending over a thousand quid putting scaffolding up, ripping out cupboards inside the flat etc all for this tiny issue which in no way affects the boiler performance. I’d rather wait for my boiler to fail and if/when that happens (in about 10 years if it has the same life as the last one) I’d have to put in a new flue then anyway to be compatible with the new boiler at which point I would make sure that I specified a boiler with a flue that had a plume management kit option so that I could exit at the same place as I do now and use the plume management kit to get the exhaust gasses up to within 1m of the roof.

This is all made more frustrating by the fact that there are 7 other old boilers venting into this light well that don’t seem to be getting issues. I am getting grief because my vent is about 2.5m below the top of the light well (vs 1m under new regs) but has no windows or other vents or any habitable space above it whereas all but one of the other boilers are on lower floors so many metres below the top of the light well with other people’s windows above them. I don’t know how those people get their boilers serviced without the engineers condemning them. Maybe they all have slightly dodgy people doing the servicing or maybe I just got very unlucky.

- Julian

[Itsallaguess]

I could then simply push the pipe about 10cm in so that I end up with the discharge pipe protruding about 15cm from the end of the metal as it was before.

That sounds like a pretty good plan, and at the very least it would reinstate the improved spatial disconnect between the extended end of the inner outlet and the inlet-grill, which would improve the quality of the air being sucked back in.

Cheers,

Itsallaguess

[Julian]

I could then simply push the pipe about 10cm in so that I end up with the discharge pipe protruding about 15cm from the end of the metal as it was before.

That sounds like a pretty good plan, and at the very least it would reinstate the improved spatial disconnect between the extended end of the inner outlet and the inlet-grill, which would improve the quality of the air being sucked back in.

Cheers,

Itsallaguess

And the boiler engineer won't be able to see what I've done since he can only look out at the side of the flue from a window about 5 metres away from it . It should look like a brand new replacement terminator, exactly like the black one you first linked to since it's black pipe that I've just ordered.

- Julian

[Julian]

For anyone who is interested, the repair went extremely well. The 25cm length of 75mm outer-diameter pipe that I ordered arrived on Thursday and I went out and fitted it on Friday (yesterday).

Things never seem to work out this well when I do this sort of stuff but in this case the wall thickness of the existing flue discharge pipe is such that the inner diameter is pretty much exactly, to a fraction of a mm, the 75mm I hoped for so my new length of pipe slipped inside the existing one absolutely perfectly - tight enough that some gentle twisting was involved in getting it in but no real force required at all.

I set the new inner/inserted pipe such that about 13cm is sitting inside the existing flue discharge pipe with the remaining 12cm sticking out of the end. I sort of did it by eye to make the amount new pipe projected look exactly like the original projection as judged by photos of the flue replacement part. If anything I think I might have erred on the side of caution and my new pipe might be projecting just a little bit further than the old one did (maybe by 1 or 2 cm) but I can't see any problem with that because it's in a sheltered light well so no danger of any impact and even if there were the new pipe is way more solid than the original projecting pipe was, plus the extra projection actually increases safety because it gives a slightly bigger separation between air intake and exhaust efflux points than the original termination did.

I was also able (with some difficulty as it was a bit rusty) to retract the single retaining screw that went through the metal flange on the metal part end cap and through the current flue pipe to secure it (I actually had to retract that screw anyway to get the new pipe in since the tip of the retaining screw projected a couple of mm inside the existing flue pipe). I then drilled a hole in my new pipe at the right point, slid the new pipe in to the correct depth and at the right orientation so that the holes through the old and the new pipe lined up, and then screwed the retaining screw back down so that it now acts as a physical lock for both the old and the new pipe such that I don't have to rely on friction alone to keep the new pipe in place (although it is a tight enough fit that I am sure that would have been OK but better safe than sorry).

All in all I'm delighted with my repair and, rather than compromising the flue, I think if anything I've enhanced its robustness and safety characteristics. That's a very expensive bullet dodged. All of this also finally prompted me to do something that shamefully I've never done before in my life which is to install a carbon monoxide sensor inside my house to complete my exercise of being absolutely sure that I haven't compromised safety in any way.

Special thanks again to you itsallaguess (if you're reading this) for acting as a sounding board as I went through my various stages of panic and planning re what to do. It is so great to have such people around here to bounce ideas off, offer other options and ideas even if some don't pan out, and generously spend their own time searching for stuff on the internet on behalf of others. Yet another example of what a great community this place is.

- Julian

[Itsallaguess]

All in all I'm delighted with my repair and, rather than compromising the flue, I think if anything I've enhanced its robustness and safety characteristics.

Good job that man!

How long is the scaffolding still up for?

It's just that you've not mentioned the anti-nesting grill on the end of your new pipe...

Cheers,

Itsallaguess

[Julian]

How long is the scaffolding still up for?

It's just that you've not mentioned the anti-nesting grill on the end of your new pipe...

It comes down on Tuesday.

You're right and I should revisit that if I can. It was something I thought about but I now realise that I pushed it to the back of my mind.

I have to make a trip to Homebase tomorrow for something else so I'll scour the aisles looking for something I can adapt. (I seem to do that a lot whenever I visit DIY stores.) If the worst comes to the worst I could probably fashion something that is better than nothing by cutting up some old coat hangars and twisting or cable-tying them together. Obviously I need to be very careful that whatever goes in is securely fastened so that it can't travel backwards into the flue. I also want to make sure that whatever I do isn't visibly a DIY job when viewed from the kitchen window so that I don't get any boiler servicing engineers refusing to work on it. I think I can think of a few solutions though that should be rock solid.

If I can't do it I'm not in a blind panic. The anti-nesting grill has been missing for at least 5 years from when the end pipe started crumbling and I assume it fell out. Also the light well is about to have bird netting installed over the top of it so there should never be any birds able to get to the opening anyway. Still, better to have it than not. Thanks for the nudge on this.

- Julian

[Itsallaguess]

I have to make a trip to Homebase tomorrow for something else so I'll scour the aisles looking for something I can adapt. (I seem to do that a lot whenever I visit DIY stores.) If the worst comes to the worst I could probably fashion something that is better than nothing by cutting up some old coat hangars and twisting or cable-tying them together. Obviously I need to be very careful that whatever goes in is securely fastened so that it can't travel backwards into the flue.

I'm not sure if Homebase do them, but if you've got a B&Q or Screwfix local then the FloPlast Leaf-Guards might be worth a look, as they should just slip into the end of your pipe and would look the business I would think -

https://www.diy.com/departments/floplast-gutter-balloon-outlet-guard-dia-68mm-black/35246_BQ.prd

https://www.screwfix.com/p/floplast-balloon-leaf-guard-black/68030

Cheers,

Itsallaguess

[fisher]

Chicken wire is another option although you might have to use more screws to hold it in place.

[Julian]

Thanks both of you. I think a FloPlast leak guard might work perfectly....



The inner diameter of my outlet is 69.2mm. That trap is specified at 68mm and it looks as if there's some flaring out presumably beyond 68mm that would probably give it a snug fit anyway. If it doesn't then I can bolt spacers onto the outer faces of its "flaps" to increase its flare and hence pressure against the inside of the tube. I could anchor it very securely I think by drilling a single hole through the pipe and then through one of the flaps for a retaining screw on the far side of the flue where it isn't visible from the kitchen window but that might not be necessary depending on how solid the compression fit is. Just to be 100% paranoid I might drill a big hole through the centre of that circular joining plate at the top just to make sure that I'm not creating any more back-pressure than I have to but apart from that it really does look perfect.

I'll go and pick one up tomorrow and give it a go. I'll also pick up a sheet of 13mm mesh (https://www.diy.com/departments/grey-me ... 568_BQ.prd) so that I have everything for a chicken-wire plan B. I've been wandering around the house looking for circular plastic containers that are close to but not exceeding 69.2mm which I might be able to cut the top and bottom off to form a frame around which I could wrap the wire mesh, slip that whole assembly into the end of the outlet, and again physically secure it with a single screw or bolt through it and the outer tube. I've found a container of nice solid plastic that is 63.8mm diameter which would probably be just about perfect to wrap a mesh over, the wrap-over would bulk it out to the desired 69.2mm.

Between one of these ideas I'm sure I'll end up with a very satisfactory anti-nesting guard by this time tomorrow. B&Q is a bit further away from me than Homebase but no big deal and the B&Q web site says that my local store has both items in stock so that's where I'll go.

- Julian

[fisher]

It may also be worth buying some clear silicone and applying some clear silicone around the plastic leak guard's fins before you push it in place, or around the inside of the pipe if you prefer (or as well). This will then set and hold it in place. I would use this rather than screws myself, but if you like then use both.

[fisher]

Thanks both of you. I think a FloPlast leak guard might work perfectly....

How did you get on?

[Julian]

Sorry, I meant to update this but got caught up with other stuff.

I ended up using that FloPlast leaf guard. It didn't fit that snugly so I ended up using some heavy duty exterior-grade silicone on the flaps but I couldn't really get much compression to make the joint good and it wasn't possible to get the nozzle through the guard once in place to secure it from the edges of the flaps so I had to smear the outside faces of the flaps with silicone, slide the guard in, and then press things down with a screwdriver and hope I got some sort of adhesion between the outside of the flaps and the inside of the tube. I didn't want to test it too much in case I compromised whatever partial adhesion I had managed to get.

Marginal adhesion isn't too much of a worry though because I also had the bright idea of getting some solid wire and twisting one end around the circular bit of the guard (where the flaps join onto the dome structure). I then took that wire out of the opening, bent it 180 degrees back on itself so that it was then running down the outside of the metal flue directly back towards the wall, and then did another twisted-loop-around connection through a couple of the vent holes close to the wall. This gives a good physical restraint so that the grill can't possibly get either pushed/fall into the flue and neither can it somehow fall out so I think it's very solid. The length of the flaps on the grill unit also means that, even if there is no adhesion, the grill might go a bit skew in the opening by maybe 5 degrees off axis but it can't actually rotate round much at all so the dome is going to remain facing outwards and giving full protection.

The scaffolding finally went down yesterday. That's such a relief. It was horrible when even during the brief 25C bright sunshine days that we had a few weeks ago (at least in London) to come into the kitchen at lunchtime and have to turn on the lights because it was too dark to see properly. My mood has lifted noticeably now that I have daylight in my kitchen and my home office that were the rooms blighted by the scaffolding where I had to have the lights on for the whole daytime.

The acid test on the flue will be when I reschedule the service visit but I don't think there's any way of telling that it's not a new replacement part except for the fact that the tube sticking out of the end is dark grey not black or clear plastic but I can't imagine that most boiler engineers will be familiar with that level of detail regarding a 12-ish year old boiler part. (The outlet tube on the modern equivalent flue looks very different because it is designed to be able to take a plume management kit - it is actually detachable as well as opposed to mine that isn't.)

Thanks again for all the advise and support.

- Julian