Installing a new defrost sensor often resolves this

As a direct replacement for 5H73034

The Maxitrol 325-9-1 1/2-12A49 is an industrial-grade

Industrial-Grade Bearings: Built to withstand continuous operation while maintaining low noise levels and minimal vibration

Laars Heating Systems RS2112801 Burner Door 321702-401 Installing a new defrost sensorThe Laars RS2112801 Burner Door with Gasket is a critical OEM replacement component designed to maintain the integrity of the combustion chamber in Laars NeoTherm (NTH) Boilers. Engineered for high efficiency hydronic heating systems, this assembly ensures an airtight seal between the burner and the heat exchanger. This model is specifically compatible with a wide range of NeoTherm units, including the NTH 150, NTH 210, NTH 285, NTH 399, NTH 500, and