On 13/01/2013 17:35, Dave Liquorice wrote:

2nd Year of running the woodburner. Didn't think it was drawing very well
the last few days, wasn't sure if it was because of the cold, still,
weather or something else. So removed the baffle to look at the base of
the 7" rear exit flue. Maybe more than 50% blocked by light
crispy/brittle tar bits, removed all that (a bucket full) and it's now
drawing and burning far better. B-)

My wood burner is broadly comparable with yours in power and a back
boiler. My observations are that I have had the same thing happen as you
but it was because I was burning up the last bits of coal on it.

Mine is capable of running dual fuel. The most likely cause of your
build up recently is that the top of the chimney where the flue gasses
meet the cold external air is starting to neck a bit with condensing
tar. My sweep recommends burning a small amount of smokeless fuel in the
mix to make the burning wood soot less inclined to plate out as tar and
easier to dislodge. I don't yet know if his advice is sound.

I don't know about yours but mine said the baffle plate should be
checked weekly for any obstructions - probably CYA H&S regulations. I do
it about monthly or if I have trouble lighting it.

The flue was swept before we started this season in the last week of
October, similar amount of burnt tar then after the entire winter (5
months?) as I've just removed after a week under three months.

The air draw is decreased so more tar, soot and smoke formed. You can
probably keep it running by checking the baffle plate a bit more often
and then getting the sweep in to check over the chimney. My money would
be on a constriction right up at the top from what you have described.

Just seen your description of the flame patterns which sounds more like
the situation I get when I damp mine right down for the night. Relights
nicely from the embers. Do you have a carbon monoxide alarm in the room?

There has been a fire in it most days since the 23rd Oct from about 1500
with the last logs going in about 2100. The stove is quite large 10kW
output but with a boiler rated aroud 7kW so I guess the flue gases are
generally quite cool. We are burning seasoned hard wood (mostly beech but
some birch and a little possibly oak), with the bark falling off and
shakes opening up in the end grain. Generally it'll get through 4 x 9"
long 4" sized logs every hour, so something over 15 logs/day.

Is that level of light crispy tar build up sort of expected? I don't mind
digging it out every 6 weeks or so, more concerned about buildup in the
flue and risk of a fire up there...

The worry is that you have a build up right at the top and plating out
of tar in the pipe and at some stage the whole lot decides to make a
chimney fire which tends to devalue the steel lining somewhat.

--
Regards,
Martin Brown