The "/U" suffix denotes a universally packaged version of the identical Honeywell gauge

you must use a model like the TRR00825 or a multi-tap transformer with appropriate primary windings

With the furnace off

This is often a sign of a cracked or fouled hot surface ignitor that can no longer reach the required 1

For LP conversions or specific LP-fired boilers

Carrier LH39WD020 Pilot Orifice Els PW 17895 The "/U" suffix denotes aAs an HVAC technician, you know that precise gas flow is the difference between a clean burning system and constant service calls. The Carrier LH39WD020 Pilot Orifice is a genuine OEM replacement part designed for high performance gas furnace ignition systems. This specific pilot burner orifice is engineered with a calibrated aperture to ensure the exact metered flow of gaswhether natural gas or propanerequired to maintain a stable and reliable pilot