A.O. Smith TWI 35-130 Security of the water temperature, Gas control, 2.4.4 Fan, Device, Remark

2.4.2Security of the water temperature

The safety switch or ECO (Energy Cut-Off) switches off the device when the water temperature exceeds 95 ºC. As soon as the temperature has sufficiently dropped, the ECO is reset automatically. Contact the installation engineer if the ECO repeatedly switches off the device.

2.4.3Gas control

The electronic control opens the gas control allowing supply of gas to the burner. The gas control has two valves as a safety device. Both valves shut off the gas supply.

2.4.4Fan

The fan (10) ensures optimum air supply during the heat demand. In view of safety, the fan makes sure that the combustion chamber is purged before ignition takes place. This is called pre-purging.

2.4.5Air pressure switch

The air pressure switch guarantees discharge of flue gasses and supply of air during pre-purging and operation of the device. The air pressure switch is typically open. When the pressure difference is sufficient, the pressure switch closes. If, however, a disturbance occurs, the pressure switch opens again and the heating cycle is interrupted. The table gives the trip points for each device.

Remark

The trip point of the pressure switch cannot be adjusted.

Trip point of the pressure switch

Device

Pressure difference

TWI 35-130

700 Pa

TWI 45-190

370 Pa

2.4.6Ionisation detection

The electronic control uses the hot surface igniter for flame detection by means of ionisation detection. The electronic control closes the gas valve as soon as it observes that there is no flame while gas is flowing.

Instruction manual TWI 35-130 G/TWI 45-190 G 13