Over heat cut out thermostat (Set @ approx. 90 – 98 degrees C)
Reasons to activate an over heat cut out thermostat
- Scale / magnetite deposits causing excessive heat build up
- Loss of system water
- Loss in manufacturers calibration
- Faulty pump or pump speed too low
- Too much air within system water
- Faulty expansion vessel (loss in air charge or split diaphragm)
- Faulty gas pressures / solenoid stuck in on position
These thermally activated control devices may interrupt the electricity supply to a gas solenoid valve extinguishing the pilot and/or main burner, signalled by the printed circuit board. The overheat cut out thermostat must be manually reset to prevent further boiler cycling whilst a fault may be present (overheat lockout).
To test an over heat cut out thermostat (when not at trip point):
- Electrically isolate boiler / system controls
- Remove wires from thermostat terminals
- Set multimeter on ohms scale for resistance readings, across thermostat terminals:
- Continuity across terminals = ok, No continuity across terminals = faulty
To test an over heat cut out thermostat (when at trip point reaching 90-98 degrees C)
- Electrically isolate boiler /system controls
- Remove wires from thermostat terminals
- Set multimeter on ohms scale for resistance readings, across thermostat terminals:
- No continuity across terminals = ok, Continuity across terminals = faulty