Blocked chimney? Gas fire not drawing

[amfisted]

Went to put our coal effect gas fire on last night for the first time since perhaps the beginning of April. No problems, sat there nice and comfy. Did the same at teatime tonight and immediately noticed a different smell, a bit like real coal burning. I also noticed a lot more heat coming off the fire than usual, indicating that very little was going up the flue. I even went up on the roof and there was no hint of any warm air coming out of the pot.

Next thing the red alarm light on our CO detector started flashing like crazy, and eventually it began to shriek like a banshee.

Off went the fire, out came the head scratching fingers and eventually I concluded, not unreasonably, that there must be a blockage. Presumably a bees' or wasps' nest because we have one of those slotted metal caps on the top of the chimney pot, so no chance of a bird getting in. However, I hadn't heard any buzzing within the flue during the summer nor seen insects hanging around the top of the stack.

Its a modernish house so I didn't think there had been any kind of collapse, nor could I see any blockage when I used a mirror and head torch to look up the flue.

Long story short: got my drain rods out, put the small drain brush on the end, inserted carefully into the chimney, hit what felt like the bottom of the metal cap, went on the roof to check and yes, the brush was up against the underside of the cap, back down to the lounge and wiggled the brush, resulting in bits of what looked like dirty granular loft insulation coming down into the fire, removed rods and relit the fire. All was clear, there was no 'orrible smell and the CO alarm was happy.

Thing is, hardly anything came down--no obvious nest, only a small quantity of this granular material. Is it possible that a spider's web might have been spun inside the flue during the summer months, and that dust and dirt had settled on it resulting in the chimney being blocked? Seems unlikely to me.

Cheers for reading if you got this far. Any other possibilities come to anyone's mind?

 

[KenGMac]

amfisted, good evening.

In the intervening period between using the Fire have you had cavity wall insulation installed?

Just a thought?

Another thing to consider is to have a smoke test undertaken on the Flue, by a Professional, in situations where the CO alarm triggers UNDER NO CIRCUMSTANCE take any shot cuts whatsoever, AT ALL AT ALL AT ALL!!!!!

Did you instruct the installation of the appliance? if not then I would be very cautious about a potential life threatening situation, of which you are fully aware.

Ken.

 

[amfisted]

Hi Ken

No, we've had no work of that kind done since moving here just over 2 years ago. Cavity wall insulation was had already been installed by the previous occupier, and that would have happened at least a decade ago, probably longer. Its an internal flue which goes through the middle of the house, so it's nowhere near any outside wall that might contain insulation material.

The fire was already fitted when we moved here. The box was taken out and serviced by a Gas Safe engineer a year ago; he did all the relevant tests and we used it last winter without any problems.

We did have an inundation of red mason bees which were nesting under the roof tiles, but as you'll know they're solitary insects so would not have constructed a hive in the flue;although some did come down the chimney one Saturday about a year ago in their search for nesting sites. Following that incident the fire continued to work properly. Nor, as I said in my first post have I seen any wasps or bees reguarly hanging around the chimney stack this summer.

I can only assume something has happened during the summer months, such as a spider's web being spun within the flue and then accumulating dust (but from what source?) because to me at least there's nothing else that can possibly explain what's happened.

I'm going to get a full sized chimney brush to fit my drain rods and make sure the flue is properly cleaned before using the fire again, and in any case we're currently looking to have a woodburner put in so the flue will shortly receive some professional attention.

Thanks again for your response.

 

[bernardgreen]

For the combustion products to go up the chimney there has to be a source of fresh air for the fire coming into the room to replace the air taken up the chimney. If there is no way for fresh air to get into the room to supply the fire then combustion products will not go up the chimney. Have you draught proofed the room ? Have you closed off any air vents, have you used a draught excluder to block the gap under the door ?

Another reason could be wind from a certain direction creating air pressure at the top of the chimney that is higher than the air pressure in the room

 

[Hugh Jaleak]

Cut out the guess work, this is yours and your family's life at stake here!

Get a Gas Safe engineer who is qualified to work on gas fires to look at it, and DO NOT USE it until it has been declared safe.

There could be a number of reasons why CO is being produced, not all of which may be obvious. Until it is checked, do not use, you probably owe your life to that CO detector already! No-one can advise correctly without being in front of the fire and having the equipment to carry out the requisite tests required to ensure that appliance is safe to use.

 

[Hugh Jaleak]

I think due to the seriousness of the issue here, this thread maybe better in the Plumbing section, Gas appliances are not a Builder's subject. Will see if the Mod's can move it.

 

[amfisted]

Thanks all for the replies.

We had the fire checked last year, as I said above, and it worked fine throughout last winter without any unusual smells and without triggering the alarm.

There is an air vent in the room which was blocked by a piece of hardboard behind an internal plastic vent cover when we first moved in. A gas safe engineer told us on the first occasion when the fire was serviced, which was in 2014, that this vent should be unblocked. Last year a different engineer came to do a second service and told us that because the fire output was less than 5kw there was no need for an open air vent in the room so I closed it off again, and it remained closed last year. No other work has been done to draughtproof the room since last year, and nothing has been done to the flue.

We have a HETAS engineer coming tomorrow to do a survey for replacing the fire with a woodburning stove, so I'll ask him to do a smoke test and if possible to inspect the interior of the flue whilst he's here.

And I won't use the fire again until it has a clean bill of health, or until its removed and replaced, whichever comes first.

 

[ajstoneservices]

Is it possible that a spider's web might have been spun inside the flue during the summer months, and that dust and dirt had settled on it resulting in the chimney being blocked?

Yes, a common problem.

 

[amfisted]

Yes, a common problem.

Seriously?

 

[amfisted]

Yes, seriously.

I've just had a look online and its not uncommon at all, though when I posted it as a possible reason for the fire not working properly I was admittedly clutching at straws.

Still, we'll have the necessary tests done before using the fire or a replacement.

 

[Hugh Jaleak]

Please do. CO is produced as a result of burning fossil fuels, when there is insufficient oxygen to allow correct combustion, so a wood burning stove could also produce CO under the right circumstances. Deaths have also occurred when campers have brought a portable BBQ inside the tent for a bit of warmth, starved of air CO has been produced which has then killed them!

 

[amfisted]

I will, thanks.

Another thing that occured to me (and I have yet to test whether this can be addressed by opening up the air vent because I don't want to use the fire until its been checked) is that I fitted a more powerful kitchen extractor fan last year. My wife, who suffers from respiratory problems, says that unless she opens the back door, then on its highest setting the extractor sometimes draws so much air out of the kitchen when she's using it that it causes her shortness of breath.

If the extractor is in use and the air vent in the room where the fire is remains blocked up, then presumably that would have an adverse effect on the ability of the chimney flue to provide an adequate "draw".

It's a bungalow, by the way, so all this is happening on the one floor.

 

[ajstoneservices]

kitchen extractor fan

Can reverse flue flow.

 

[bernardgreen]

If the extractor is in use and the air vent in the room where the fire is remains blocked up, then presumably that would have an adverse effect on the ability of the chimney flue to provide an adequate "draw".

That is 99% certain to be the problem

 

[ajstoneservices]

No it's not.