Terrible, sudden creosote problem in flue.

[RigidRaider]

Can anybody shed any light on this? We have been using multi-fuel stoves for 20 years without problems. We have used our stove (Dovre 250) in our house since 2004 without any problems. The flue is un-lined clay sections a little bigger than the stove pipe in an outside wall chimney.

It started last Autumn when we burned some larch our supplier gave us and began to get brown liquid dribbling out of the register plate and down the back of the fireplace. We stopped burning the larch and the dribbling stopped. Aparently larch is notorious for this. By the way the meter shows that our wood has 12-14% moisture.

Two weeks ago our sweep came and he and I dismantled the stove pipe and cleaned everything up. He power swept the flue and it looked clean with no sign of damp or dribbling. He used a heatproof silicon sealant on the register plate so we had to leave it unlit for four days but when we re-lit the stove the problems began, worse than ever. Water begain dripping down the back and front, onto the stove pipe, hissing and evoporating and making the house stink. At one point it was dripping out of the collector at the base of the flue at a drip a second; we collected half a pint of smelly brown water. We are shocked at the change and can't work out the reason. We have tried burning only smokeless nuggets (Pureheat) and getting a really blistering hot grate temperature (into "too hot" on our little indicator dial.) We have tried lighting and getting up to temperature with only hardwood. Nothing we have tried has stopped the flow. Last night on a very hot grate lit several hours earlier I added two dry logs and opened the vent to full and within ten minutes brown water was dripping out of the flue and hissing on the stove pipe.

We think the problem may be partly because the flue is so clean that there is no soot to hold the inevitable moisture and it just runs down. Our sweep has suggested drying the smokeless fuel before using it as it does come a little damp from the supplier. We are sure our wood is fully dried; as I wrote moisture meter readings are 12-14% and we even dry the logs for a week alongside the stove before burning them, so that the radial cracks are really opening up.

We moved into the front room while the lounge flue was out of use, where we have an identical stove with an identical flue and chimney and we used the same fuel. That chimney has had very little use. We had no condensation at all.

Anybody got any words of wisdom? I am going up on the roof to check the cowl and the flaunching this afternoon as it's dry but no water came down the flue while it was unused and it rained heavily.

 

[lostinthelight]

When you measure the moisture do you take the reading in the middle of a freshly spit log?
Did the sweep use nylon whips or chains and how often is it swept?
How much wood a year do you burn and is the stove running low a lot?
Can you post some pictures of chimney stack,outside wall,pipework from stove a nd inside the stove,just far enough away to see the open doors?
litl
edit.
Has the stove a boiler fitted

 

[RigidRaider]

Thanks. No back boiler in either stove. The fumes emerge from the backs into a T then head vertically through the register plates and from there the flues are unlined. We get through about three builder's bags a year of mixed hardwoods. I have actually weighed a sycamore log freshly-cut then seasoned in our store and it lost 43% of its weight. What we get from our supplier is much drier than that, it's half seasoned when we get it, already ringing and cracking radially, then we store it in a south-facing open store with a roof, in a very breezy spot and are usually burning the Spring delivery by December. I haven't split a log and measured on the exposed grain, no, but will do.

The flue gets swept every November and this time he used a nylon whip brush, rotating and thoroughly reamed up and down until the flue was spotless though black. Less than a bucket full of soot came out, which is from a couple of months of burning.

The stove does get idled later in the evenings when the grate is really glowing hot and clean; we usually start wiith kindling, add some nuggets of Pureheat then turn it down when the nuggets begin to glow. Once they are fully glowing we add logs onto the bed of embers and keep them topped up all evening. This could be where we are going wrong; last night I lit with kindling and logs only and left the door adjar for a good hour until the logs were almost exhausted and really glowing hot before adding nuggets and.... no condensation. I'm beginning to think that the speed of the fumes up the cool flue has a lot to do with it. That still doesn't explain why the problem has suddenly started in the lounge flue after 20 years of using the same stove in two different houses and now in two identical flues.

 

[Nige F]

Can anybody shed any light on this? We have been using multi-fuel stoves for 20 years without problems. We have used our stove (Dovre 250) in our house since 2004 without any problems. The flue is un-lined clay sections a little bigger than the stove pipe in an outside wall chimney.


Anybody got any words of wisdom? I am going up on the roof to check the cowl and the flaunching this afternoon as it's dry but no water came down the flue while it was unused and it rained heavily.

I had a chimney similar - clay liners - flaunching looked ok but water was getting in + down the flue. I went up ( bungalow luckily ) and poured brickwork sealer all around and over the flaunching, particularly against the liner poking out - stopped the leak - I think you may have water getting in and wetting the outside of the liners, making them cold, maybe all the way down ? BUT not showing any damp on walls etc. Why ?? because I've seen a few vent pipes through roofs, with lead flashings but without the important weathering collar glued on . The water marks can be seen @ ground floor level ! So water can get in small cracks, more than you would think

 

[RigidRaider]

Good suggestion. I couldn't go on the roof because it was too wet but had a look at the flaunching with binoculars from a neighbour's window and it looked OK but it might be cracked or even porous so I will definitely have a look this spring.

 

[Burnerman]

If the stove pipe is slightly smaller than the chimney - which it will be, naturally enough - there will be a soot deposit building up on the top of the register plate when the lum is swept. Its important to remove this as it can promote a fire there. Is it easy to drop the register plate a fraction to get a vacuum cleaner into the void?
John

 

[RigidRaider]

We cleaned all that thoroughly when I dismantled it two weeks ago with our sweep. I think it's the cleanness of the flue that's allowing the condensation to dribble down. More soot might hold onto the moisture for longer.

I'm beginning to understand that we had slipped into the habit of piling smokeless nuggets onto kindling and overwhelming the fire with too much cold damp fuel. We were also closing the door too early. That was causing cool combustion temperatures and cool smoke hanging around in a cool flue. When you went outside the smoke would be emeging from the cowl very sluggishly and not really rising, so it was cool. We have now lit for three evenings leaving the door open for almost an hour to get the temperature up fast and the smoke rising well and we've had no more condensation.