Biomass flue safety question

edited 30 November -1 at 1:00AM in LPG, Heating Oil, Solid & Other Fuels
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We have a MCZ Red Compact 14 that was installed Dec 2013.

One issue we have had is in regard to the complete combustion of pellets. From the start we have had partially burned pellets in the amongst the ash.

The issue was original pointed out to us by our (MCS accredited) installer and having access to friend who has the slightly larger MCZ Compact red 18 model, I know that the ash should be fine and have no partially burned pellets.

Various attempts of changing boiler configuration have been made (by the installer) to fix this issue and the last attempt to fix the issue involved adding a damper vent to the base of the flue (inside the room where the boiler is installed). This means that when the boiler starts up smoke comes out of the damper vent and enters the room. It clears within a few minutes.

Being well aware of the dangers of CO poisoning, we have two CO life safety alarms installed near the boiler (both have been functionally tested - not relying on a button test). One CO alarm was fitted by the installer and the other I have fitted which has a Parts Per Million (PPM) LED display. At no point has either of the CO alarms activated and the PPM read out has remained at 0 at all times.

Common sense tells me that it is not a good idea or safe to have part of a solid fuel flue vent into a room. My installer and the importer are claiming that this is acceptable practice.

Does anyone have a similar set-up or have any knowledge of HETAS standards for flues?

Appreciate any help.

Paul

Replies

  • tonyh66tonyh66 Forumite
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    doesn't sound right to me, perhaps you should try a different HETAS installer see what his opinion is?
  • sounds like a flue draught stabiliser they have fitted, is it just above the boiler ? by fitting this they are saying the draw on the flue is too much and could be possibly overfiring the appliance or taking it out of its best efficency by drawing too much heat up the flue. Was any ventilaton fitted with the appliance vent to outside in same room ?
  • [Deleted User][Deleted User] Forumite
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    we have an mcz hydro 15 and have a large hole in the floor connected to an outside air intake, the hole is near the stove air intake point. Our ash is fine and there is very little of it. I am no engineer but incomplete combustion sounds like a lack of enough oxygen to the fire. Re the smoke in the room, this should not be happening and while there is no carbon monoxide, there is toxicity from wood smoke. I actually have a good air filter close to my stove as there is always a chance of a waft down from the flue while the flue is cold or if the wind is not right but it is only a waft and only infrequently

    I would follow chimney sweeps post and check that the air intake to your room is adequate and also check that you are using enplus pellets and not horse bedding pellets
  • Thanks all for the reply's
    sounds like a flue draught stabiliser they have fitted, is it just above the boiler ? by fitting this they are saying the draw on the flue is too much and could be possibly overfiring the appliance or taking it out of its best efficency by drawing too much heat up the flue. Was any ventilaton fitted with the appliance vent to outside in same room ?

    Originally the boiler had a direct (air intake) connection to the outside. The pipe connecting the boiler to the outside has since been removed and it is now drawing air from within our utility room (warmer air?). The large air brick is till there (open to the outside) and I imagine will cause a draught in the winter.

    Yep, you are correct it is a draught stabiliser that has been fitted (fitted at base of flue behind boiler). The issue (unburned pellets) might be related to the flue length. We are in a house and the other MCZ (small 14 & 18) boilers I know are installed in single storey bungalows (shorter flue length) and this maybe why they don't have the same problem as we do.

    We also have had an igniter replaced (under warranty) which failed after about 3 months use. This was at the time we were getting errors which have since stopped being displayed.

    My installer is HETAS qualified and is coming tomorrow with the MCZ agents to see if anything can be done.

    Appreciate any help.

    Paul
  • you cannot just put a stabiliser in they need to be set with a draught gauge, they have an adjustible counter weight which keeps it closed (and fumes within flue) until the draught becomes excessive it then opens and allows air to bypass the boiler.
    Not familiar with pellets stoves as there are a lot of other variables but unburnt pellets I would guess at too little draw to burn efficiently, but they increase the pellets feed rates with temp, so they could be correct that the draw is too much meaning high temp and too many pellets going in to be burnt, so slow the draw and thus temp and see what happens. Let us know what happens hope the manufacturer rep can sort it someone at least should get a draught gauge on it if thats not been done yet.
  • RickMoneyRickMoney Forumite
    153 Posts
    Part of the Furniture 100 Posts Combo Breaker
    I don't have one installed yet, but I do intend to get a MCZ one. When I was at the retailers about 2 months ago, he was showing me the latest models (with the glass frontage) rather than the compact grey ones. He made a comment that these newer ones have had the design of the crucible improved to ensure the full burn of pellets.

    This guy has had one in his own house for years and is well versed in the brand and the reps.

    So without being technical, it might be worth checking if it is down to the design of the crucible on the model rather than a problem with the set up?

    Rick
  • Suggest you talk to Specflue, they are the importer.

    I have a Kalorina pellet boiler at home, have had it in about 7 years so have a bit of experience.

    Unburnt or partially burnt pellets is usually caused by to many pellets being loaded into the firebox soon after the fire is restarted. To cure that I slow down the speed of the loading auger, this reduces the volume of fuel pushed into the crucible. When burning cerials in mine I have in the past swamped the fire and put it out !!.

    Another issue may be the fan under the fire running to fast and actually blowing part burnt pellets out of the top of the fire cruciable.

    I hasten to add that while I have buy flue parts from Specflue I have no experience at all with their pellet boilers. They are though a decent company.

    A
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