Grün Engineering
Guides

For facilities managers

Common flue faults we find on surveys.

Real photos from our surveys and condition reports. What each fault means, and what we do about it. Sites aren’t named.

Close-up of a leaking joint on a stainless flue with brown and yellow condensate staining down the seam
Survey photo. A leaking joint on a boiler flue header.

What we do about it

Survey, fix, prove it.

  1. 01

    Survey

    We measure, sketch and photograph the system, with CCTV normally from the terminal down.

    What happens on a survey
  2. 02

    Repair or replace

    Failed sections, seals, brackets and terminals put right, or a new system where it’s past saving.

    Service and maintenance
  3. 03

    Tested and certified

    Pressure or smoke tested, with test reports and a certificate of conformity where applicable.

    Testing and surveys

8 faults we see.

All photos taken by our engineers on surveys.

  • Close-up of a leaking joint on a stainless flue with brown and yellow condensate staining down the seamSurvey photo

    Fault 01

    Leaking joints and failed seals

    Brown and yellow staining around a joint means condensate and flue gas are getting out. The acid in it eats the metal around the joint.

    What we do about it

    We check every joint on the survey, replace failed sections and seals, then pressure test and give you a test report.

  • Long horizontal stainless flue run at ceiling level along a corridorSurvey photo

    Fault 02

    No fall on horizontal runs

    A long horizontal run needs to fall back to a drain. With no fall, condensate sits in the pipe and works its way out through the joints. On this survey it was the cause of several leaks.

    What we do about it

    We measure the run, redesign it with a proper fall and drain, and replace the horizontal sections.

  • Water staining on the boards around the base of a flue where it passes through a riser floorSurvey photo

    Fault 03

    Staining around penetrations

    Staining where a flue passes through a floor, wall or roof means water or condensate is getting past it. Left alone it damages the building around it.

    What we do about it

    We trace it back, normally with a CCTV survey from the terminal down, then reseal or replace the section.

  • Stainless flue terminal sitting low behind a roof parapet with staining on the renderSurvey photo

    Fault 04

    Terminal in the wrong place

    Flue gas needs to get clear of the roof. A terminal tucked low behind a parapet can let it hang around, stain the building and find its way back in through vents or windows.

    What we do about it

    We check the terminal on every survey and extend or re-route the flue. We provide the calculations and drawings for building control.

  • Stainless flue elbow at a wall plate with rust spots on the casing and cracked sealant around the penetrationSurvey photo

    Fault 05

    Rust spots and cracked weathering

    Rust spots on stainless steel mean something is attacking it. Cracked sealant at a wall or roof plate lets rain in behind the cladding.

    What we do about it

    We replace corroded sections, refit wall plates and weathering, and inspect the rest of the run.

  • Flue support bracket strap pulled out of line around a mast, with worn paint at the fixingsSurvey photo

    Fault 06

    Distorted or failed brackets

    Brackets carry the weight of the flue and the wind load on it. When they distort or shear, the flue can move, pull apart at the joints or fall.

    What we do about it

    If it isn’t safe we make it safe on the day. Then we replace the brackets and supports and re-check the joints.

  • Twin wall flue section on the ground with broken-down insulation spilling out of the end and heavy corrosionSurvey photo

    Fault 07

    Failed insulation

    The insulation in a twin wall flue keeps the outside cool and the gases warm. When it breaks down the outer wall gets hot and more condensate forms inside.

    What we do about it

    Insulation can’t be repaired inside a twin wall section. We replace the affected sections with new twin wall insulated ones.

  • Looking down into the top of a twin wall flue where the corroded inner liner has dropped below the outer casingSurvey photo

    Fault 08

    Inner liner dropped

    The inner liner and outer casing should sit level. When the liner drops, the joints open up inside, where you can’t see them from the plantroom.

    What we do about it

    We replace the affected sections and check the rest of the flue from the top and with CCTV.

Questions

Before you book.

Do you do flue inspections and maintenance?
Yes. We carry out flue inspections, condition checks and maintenance on commercial and industrial flues.
How soon can you survey?
Normally within a week of an order.
What testing do you do?
Pressure testing with a test report, smoke testing, and CCTV flue surveys, normally from the roof terminal down. Testing is agreed for each project.
Do you do urgent work?
Urgent work is by arrangement. Call 01395 201950.
Can you work nights and weekends?
Yes, by arrangement.
What warranty do you give?
12 months on our workmanship, plus the manufacturer’s warranty on the materials.
ServiceTesting and surveys ServiceService and maintenance GuideWhat happens on a flue survey Who we helpFor facilities managers

Worried about a flue?

Survey normally within a week of an order. Urgent work by arrangement on 01395 201950.

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