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The Flue Block System

Pre-cast flues are notorious for their problems. Many of the pre-cast installations will have been installed in the 1970’s & 1980’s. Flue block systems before 1986 will require gas fires under the category of pre 1986. The information will be on the gas fire manufacturer’s instructions or at your Invicta Gas Showroom.

So what are the problems?

Many customers will wish to have a new gas fire and fireplace. This leaves the pre-cast gas fire opening quite often too high. It is not simply a case of cutting the pre-cast flue block opening to the floor level. Special pre-cast flue blocks will need to be obtained. These will need to be built into the construction of the existing pre-cast flue block system. The pre-cast flue block system would have been installed when the house was first built. After removal of the brick work below the flue block opening (this can open the cavity between the brick work of the inner and outer areas of the wall and expose cavity wall insulation) the new pre-cast flue block can be fitted.
Having the correct pre-cast gas fire opening the next problem is cracking of the plaster above the pre-cast gas fire opening. (This sometimes runs into the bedroom above). This is where the house builder will not have allowed an air space between the pre-cast flue block, which rises through the wall and the plaster finish, which would be the decorated wall in your lounge. The area above the flue will generally become warm or even hot, the expansion and contraction will result in cracks in the plaster finish.
Having the correct pre-cast opening & the wall above the pre-cast gas fire opening has an air space. The next problem will be the pre-cast flue running through the roof space. This can have too much horizontal flue, the flue pipe in the wrong material, the fitting between the flue and the ridge tile is faulty ( common fault is the bolts have sheared or they are plastic).
Having the correct pre-cast opening, the wall above the pre-cast gas fire opening has an air space and the flue running through the roof space correct. The next problem will be that the flue will not pass a smoke test when the gas fire is fitted. The first check would be the ridge tile vent this may require upgrading to the new standard flue ridge vent tile. The other common fault would be the joints between the flue blocks have oozed out into the pre-cast flue block opening and the flue is restricted so much, that the products of combustion or the smoke will not be able to pass.

If the flue is visually correct and the gas fire passes the manufacturer’s flue flow smoke test the fire can be certificated. However as the final smoke test can only be carried out on the fully installed gas fire, it often happens that it fails to pass its final smoke test. This will require a further check for partial blockages in the pre-cast flue block system or the upgrade of the flue ridge vent. (£285) and so the above has to be checked. Please note that there is no refund on the work carried out but Invicta Gas will refund the appliance for an electric fire or a flue less gas fire.

THE DECISION TO INSTALL A PRE-CAST GAS FIRE COULD BE CONSIDERED AS QUITE A GAMBLE

OUR INVICTA GAS SPECIALIST WILL ASSIST AND ADVISE BUT THE FINAL CHOICE IS YOURS!

Typical Installation project development