Ideal Limit Thermostat 173353

The Ideal limit thermostat (part 173353) is a safety sensor fitted inside Ideal Classic and Classic Slimline boilers. It monitors the temperature at its sensing point and interrupts the burner circuit when that temperature rises beyond the designed limit, protecting the heat exchanger and the rest of the appliance from overheating damage. It is a direct replacement component from Ideal Spares and sits within the thermostats, thermistors and sensors group of boiler spares.

• The boiler fires, runs briefly and then locks out, requiring a manual reset each time.
• The overheat cut-out trips repeatedly with no obvious cause elsewhere in the system.
• Heating and hot water stop altogether while the pump and other controls still run.
• The appliance reaches temperature and shuts down earlier than expected, short-cycling on the limit stat rather than the main control stat.
• Continuity testing across the thermostat terminals shows an open circuit when the sensor is cold.

• Check the GC number on the appliance data badge against the compatibility list, as several Classic variants use different thermostat arrangements.
• Confirm the existing thermostat carries part number 173353 or the alternative number 1179393 before ordering.
• Inspect the sensor pocket and any sealing washer or gasket on removal, and replace if it is compressed, hardened or damaged.