The Thermofor Long Piston Replacement is a direct replacement cylinder designed for Thermofor automatic roof vent openers used in Alton greenhouses. If your current opener is no longer responding properly to temperature changes, replacing the piston is a simple way to restore reliable, automatic ventilation.

This heat-sensitive cylinder contains a wax core that expands as temperatures rise and contracts as they cool, driving the vent to open and close naturally. It helps maintain a stable growing environment without electricity or manual adjustment.

KEY FEATURES

• Designed for Thermofor openers: Compatible with Thermofor roof vent systems used in Alton greenhouses.
• Restores automatic ventilation: Brings your vent opener back to proper working condition.
• Heat-powered operation: No electricity or batteries required.
• Replacement cylinder only: No fittings or hardware included.

SPECIFICATIONS

INSTALLATION GUIDE

For proper installation and accurate operation, the piston must be cooled before fitting. Place the cylinder in a refrigerator for approximately 30 minutes. This allows the wax inside to contract so the piston rod can be fully depressed.

Once cooled, press the piston rod firmly against a hard surface until it retracts into the cylinder. Install the unit with the vent arms in the closed position to ensure correct alignment with the vent and mounting points.

Skipping the cooling step may prevent the unit from being set correctly.

MAINTENANCE AND CARE

Keep the piston clean and free from debris to ensure smooth movement. Periodically check alignment and mounting points to maintain consistent vent performance.

FREQUENTLY ASKED QUESTIONS

What does the piston do in a greenhouse vent opener?
The piston contains a wax-filled core that expands with heat, pushing the vent open. As temperatures drop, it contracts and closes the vent.

Do I need electricity for this to work?
No. The piston operates entirely through heat expansion, so no power source is required.

Why do I need to refrigerate the piston before installation?
Cooling contracts the wax inside, allowing the piston to reset properly so it can be installed and calibrated accurately.

Will this fit other vent opener brands?
No. This replacement piston is designed specifically for Thermofor roof vent openers and may not be compatible with other brands.