Wood Fire Heater (GBT Boiler)
This is the primary heat source for the property
Quick Reference
| Item | Details |
|---|---|
| Location | TBD |
| Make/Model | GBT Wood Boiler (Geminox) |
| Firewood Location | TBD |
| Min Water Temp | 70°C (to prevent tar/condensation) |
How to Start the Boiler
Before You Begin
- Check water pressure gauge reads above 1 bar (when cold)
- Confirm boiler has electrical power
Step-by-Step Startup
1. PUSH the bypass lever (#3) (opens flue gas bypass)
2. OPEN loading door (#4) → add paper, kindling, then logs
3. LIGHT the paper
4. OPEN ash door (#7) slightly (improves draft)
5. WAIT a few minutes until fire catches
6. CLOSE ash door (#7)
7. PULL bypass lever (#3) toward you (closes bypass)
8. TURN ON main switch (#8) (orange light illuminates)
9. ADJUST temperature knob (#5) (keep above 70°C)
Never use liquid fuel (gasoline, lighter fluid) to light the boiler
Boiler Components
| # | Component | Purpose |
|---|---|---|
| 1 | Loading door handle | Opens door to add wood |
| 2 | Thermometer | Shows boiler water temperature |
| 3 | Bypass lever | Push to open, pull to close (see below) |
| 4 | Loading door | Add wood here (top front) |
| 5 | Temperature knob | Left = cooler, Right = hotter |
| 6 | Secondary air adjustment | Fine-tune combustion (2 screws) |
| 7 | Ash door handle | Opens door to access ash pan |
| 8 | Main switch | On/Off - orange light when on |
| 9 | Primary air adjustment | Controls main air flow |
| 10 | Flame sight glass | View fire through ash door |
Bypass Lever Positions
| OPEN (for lighting/reloading) | CLOSED (normal operation) |
|---|---|
 |  |
| Push lever away from you | Pull lever toward you |
Reloading Wood (Fire Already Burning)
- PUSH the bypass lever (opens bypass)
- Open loading door
- Add wood moderately - prefer 3-4 small loads over 2 large ones
- Close loading door
- PULL bypass lever toward you (closes bypass)
Mid-season advice
Don’t overload the boiler, especially in mild weather. Smaller, more frequent loads are better.
Temperature Adjustment
Boiler Water Temperature
- Turn the temperature adjustment knob:
- Left = decrease (-)
- Right = increase (+)
- Keep temperature at or above 70°C to prevent tar buildup and condensation
Room/Radiator Temperature
- Adjust the mixing valve on your heating circuit (not on the boiler itself)
- Turn gradually from minimum toward maximum until comfortable
Air Controls (Fine-Tuning)
Primary Air (Main Adjustment)
- Air control adjustment knob on front
- Left = less air (slower burn)
- Right = more air (faster burn)
- Goal: maintain glowing ember bed
Secondary Air (Combustion Quality)
- Two adjustment screws near ash door
- Right = decrease air
- Left = increase air
- Adjust with ash door closed
- Check flame through sight glass - should be neither too weak nor too harsh
Shutting Down the Boiler
- Press main switch to STOP position (orange light goes out)
- Keep doors open to ventilate the interior
- Allow to cool completely
Frost Protection
If the building may be exposed to freezing temperatures, contact a qualified professional to add antifreeze or drain the heating circuit.
Summer Operation
If Connected to Hot Water Tank
- Set mixing valve to minimum position
- Keep boiler temp at/above 70°C
- Make 1-2 good batches of dry wood per day rather than continuous low operation
- Adjust hot water temp via thermostat on the tank
If NOT Connected to Hot Water Tank
- Stop the boiler (see shutdown procedure above)
- Leave doors open for ventilation
Prevent Mixing Valve Jamming
Important
During summer, manually operate the mixing valve 3 times to prevent jamming.
Firewood Requirements
Wood Quality is Critical
Use the driest wood possible: 2 years seasoning, including 1 year under shelter
Recommended Wood Types
| Type | Quality |
|---|---|
| Oak | Excellent |
| Hornbeam (Charm) | Excellent |
| Beech | Excellent |
| Maple | Excellent |
| Fruit trees | Good (except cherry & plum) |
Log Sizes
| Model | Max Log Length |
|---|---|
| GBT 20 | 50 cm |
| GBT 30/50 | 70 cm |
Storage Location
TBD - Add firewood storage location
Maintenance Schedule
Daily
- Remove ashes from ash pan
Weekly
- Check central orifice between combustion chamber and loading area is clear
- Remove ash pan and clean exchanger fins with metal brush
- Clean flame sight glass if needed
Quarterly
- Disassemble and clean smoke box (4 screws attach it to boiler body)
Twice Yearly (Mid-season & End of Season)
- Have installer/service check and clean:
- Fan cleanliness
- Air passage openings
- Joint/seal condition
- End of season: complete cleaning, leave doors open for ventilation
Annually
- Professional inspection of all adjustment and safety components
- Chimney flue cleaning and verification
Adding Water Frequently?
If you need to regularly add water to your heating circuit, call a qualified professional immediately.
Troubleshooting
| Problem | What to Check | Solution |
|---|---|---|
| No heating | Wood supply | Ensure boiler has wood |
| No heating | Mixing valve position | Move from minimum toward maximum |
| Heating but no hot water | Hot water system | Call qualified professional |
| Hot water but no heating | Mixing valve | Check it’s not on minimum |
| Smoke in room | Bypass lever | Push open before lighting/loading |
| Poor combustion | Wood moisture | Use drier, well-seasoned wood |
| Tar buildup | Temperature too low | Keep boiler water above 70°C |
| Tar buildup | Wet wood | Use properly seasoned wood |
Emergency Procedures
Chimney Fire
Signs of chimney fire
- Loud roaring sound
- Excessive smoke
- Very hot chimney/stovepipe
- Flames visible from chimney top
If chimney fire occurs:
- Call 112 (fire department)
- Close all air controls
- Get everyone out of building
- Do not use water on the boiler
Carbon Monoxide
- Install CO detector near boiler
- Symptoms: headache, dizziness, nausea
- If alarm sounds or symptoms occur: evacuate and call 112
Water Leak
- Stop the boiler immediately
- Call qualified installer or after-sales service
Service Contacts
| Service | Contact |
|---|---|
| After-Sales Service | TBD - Add local contact |
| Geminox Consumer Service | 08 20 00 60 00 (France) |
| Chimney Sweep | TBD |
| Installer | TBD |
Safety Reminders
Critical Safety Rules
- Never use liquid fuel to light the boiler
- Never overload the boiler, especially mid-season
- Always open bypass lever before lighting or reloading
- Always keep water temperature at/above 70°C
- Never store combustible or corrosive products near boiler
- Never block ventilation openings in the boiler room
- Only qualified professionals may work inside the boiler
Related Pages
- Heating System Overview
- Fire Emergency Procedures
- Power Outage - Heat during outages